SCIENTIFIC AMERICAN SUPPLEMENT NO. 484

NEW YORK, APRIL 11, 1885

Scientific American Supplement. Vol. XIX, No. 484.

Scientific American established 1845

Scientific American Supplement, $5 a year.

Scientific American and Supplement, $7 a year.

BLAAUW KRANTZ VIADUCT IN CAPE COLONY.

This viaduct is built over a rocky ravine on the railway from Port Alfred to Grahamstown, at a height of about 200 ft. from the bottom. Its length is 480 ft. 6 in., and the width of the platform is 15 ft., the gauge of the railway being 3 ft. 6 in. The central span of the viaduct is an arch of 220 ft. span between abutments, and about 90 ft. height; the remainder of the space on each side is divided into two spans by an iron pier at a distance of 68 ft. from the retaining wall. These piers are 36 ft. 2 in. high, and carry girders 144 ft. long, balanced each on a pivot in the center. One end of these girders is secured to the retaining walls by means of horizontal and vertical anchorages, while the other end rests in a sliding bearing on the top flange of the arch.

BRIDGE OVER THE BLAAUW KRANTZ RAVINE, CAPE COLONY.

BRIDGE OVER THE BLAAUW KRANTZ RAVINE, CAPE COLONY.

In designing the structure the following points had to be considered: (1) That, on account of the great height above the ground, and on account of the high price of timber at the site, the structure could be easily erected without the use of scaffolding supporting it as a whole. (2) That, on account of the high freights to Port Alfred, the quantity of iron in the structure should be as small as possible. (3) That the single parts of the principal span should be easy to lift, and that there should be as few of them as possible. For this latter reason most of them were made in lengths of 20 ft. and more. The question of economy of material presented itself as a comparison between a few standard types, viz., the girder bridge of small independent spans; the cantilever bridge, or the continuous girder bridge in three large spans; the single girder bridge with one large span and several small spans; and the arch with small girder spans on each side. The suspension bridge was left out of question as inadmissible. A girder bridge with small independent spans on rocker piers would probably have been the most economical, even taking into account the great height of the piers near the middle of the ravine, but there would have been some difficulty in holding those piers in position until they could be secured to the girders at the top; and, moreover, such a structure would have been strikingly out of harmony with the character of the site. On the other hand, a cantilever or continuous girder bridge in three spans—although such structures have been erected in similar localities—could not enter into comparison of simple economy of material, because such a design would entirely disregard the anomaly that the greater part of the structure, viz., the side spans, being necessarily constructed to carry across a large space, would be too near the ground to justify the omission of further supports. The question was, therefore, narrowed to a comparison between the present arch and a central independent girder of the same span, including the piers on which it rests. The small side spans could obviously be left out in each case. The comparison was made with a view not only to arrive at a decision in this particular case, but also of answering the question of the economy of the arch more generally. The following table contains the weights of geometrically similar structures of three different spans, of which the second is the one here described. The so-called theoretical weight is that which the structure would have if no part required stiffening, leaving out also all connections and all wind bracing. The moving load is taken at one ton per foot lineal, and the strain on the iron at an average of four tons per square inch. The proportion of the girder is taken at 1 in 8.

It can be seen from these results that the economical advantage of the arch increases with the span. In small arches this advantage would not be large enough to counterbalance the greater cost of manufacture; but in the arch of 220 ft. span the advantage is already very marked. If the table were continued, it would show that the girder, even if the platform were artificially widened, would become impossible at a point where the arch can still be made without difficulty. The calculations leading to the above results would occupy too much space to make it desirable on this occasion to produce them. Our two views are from photographs.—The Engineer.

TORPEDO SHIPS.

Commander Gallwey lately delivered an interesting lecture on the use of torpedoes in war before the royal U.S. Institution, London, discussed H.M.S. Polyphemus, and urged as arguments in her favor: 1. That she has very high speed, combined with fair maneuvering powers. 2. That she can discharge her torpedoes with certainty either ahead or on the beam when proceeding at full speed. 3. That her crew and weapons of defense are protected by the most perfect of all armor possible, namely, 10 ft. of water. 4. That she only presents a mark of 4 ft. above the water line.

Then, he asked, with what weapon is the ironclad going to vanquish these torpedo rams? Guns cannot hit her when moving at speed; she is proof against machine guns, and, being smaller, handier, and faster than most ironclads, should have a better chance with her ram, the more especially as it is provided with a weapon which has been scores of times discharged with certainty at 300 yards. The ironclad, he answered, must use torpedoes, and then he maintained that the speed and handiness of the Polyphemus would enable her to place herself in positions where she could use her own torpedo to advantage, and be less likely to be hit herself. He then called attention to the necessity for well-protected conning towers in these ships, and prophesied that if a submarine ship, armed with torpedoes, be ever built, she will be the most formidable antagonist an ironclad ever had; and the nearer the special torpedo ship approaches this desideratum the better she will be.

A PLUMBING TEST.

A recent trial of a smoke rocket for testing drains, described by Mr. Cosmo Jones in the Journal of the Society of Arts, is deserving of interest. The one fixed upon is 10 in. long, 2½ in. in diameter, and with the composition "charged rather hard," so as to burn for ten minutes. This gives the engineer time to light the fuse, insert the rocket in the drain, insert a plug behind it, and walk through the house to see if the smoke escapes into it at any point, finishing on the roof, where he finds the smoke issuing in volumes from the ventilating pipes. The house experimented upon had three ventilating pipes, and the smoke issued in dense masses from each of them, but did not escape anywhere into the house, showing that the pipes were sound. If the engineer wishes to increase the severity of the test, he throws a wet cloth over the top of the ventilating pipe, and so gets a slight pressure of smoke inside it.

THE GAS ENGINE.[^[1]]

By DUGALD CLERK.

In earlier days of mechanics, before the work of the great Scottish engineer, James Watt, the crude steam engines of the time were known as "fire engines," not in the sense in which we now apply the term to machines for the extinguishing of fires, but as indicating the source from which the power was derived, motive power engines deriving their vitality and strength from fire. The modern name—steam engine—to some extent is a misleading one, distracting the mind from the source of power to the medium which conveys the power. Similarly the name "Gas Engine" masks the fact of the motors so called being really fire or heat engines.

The gas engine is more emphatically a "fire engine" than ever the steam engine has been. In it the fire is not tamed or diluted by indirect contact with water, but it is used direct; the fire, instead of being kept to the boiler room, is introduced direct into the motor cylinder of the engine. This at first sight looks very absurd and impracticable; difficulties at once become apparent of so overwhelming a nature that the problem seems almost an impossible one; yet this is what has been successfully accomplished in the gas engine. Engineers accustomed to the construction of steam engines would not many years ago have considered any one proposing such a thing as having taken leave of his senses.

The late Sir William Siemens worked for many years on combustion engines, some of his patents on this subject dating back to 1860. In the course of a conversation I had with him on the subject of his earlier patents, I asked him why he had entitled one of those patents "steam engine improvements" when it was wholly concerned with a gas engine using hydrogen and air in the motive cylinder, the combustion of the hydrogen taking place in the motive cylinder. He answered me that in 1860 he did not care to entitle his patent gas or combustion engine simply because engineers at that time would have thought him mad.

Notwithstanding this widespread incredulity among engineers, and the apparent novelty of the gas engine idea, fire or combustion engines have been proposed long, long ago. The first Newcomen steam engine ever set to work was used by a Mr. Back, of Wolverhampton, in the year 1711. Thirty-one years before this time, in Paris—year 1680—Huyghens presented a memoir to the Academy of Sciences describing a method of utilizing the expansive force of gunpowder. This engineer is notable as being the very first to propose the use of a cylinder and piston, as well as the first combustion engine of a practical kind.

The engine consists of a vertical open topped cylinder, in which works a piston; the piston is connected by a chain passing over a pulley above it to a heavy weight; the upstroke is accomplished by the descent of the weight, which pulls the piston to the top of the cylinder; gunpowder placed in a tray at the bottom of the cylinder is now ignited, and expels the air with which the cylinder is filled through a shifting valve, and, after the products of combustion have cooled, a partial vacuum takes place and the atmospheric pressure forces down the piston to the bottom of its stroke, during which work may be obtained.

On the board I have made a sketch of this engine. Some years previous to Huyghens' proposal, the Abbe Hautefeuille (1678) proposed a gunpowder engine without piston for pumping water. It is similar to Savery's steam engine, but using the pressure of the explosion instead of the pressure of steam. This engine, however, had no piston, and was only applicable as a pump. The Savery principle still survives in the action of the well-known pulsometer steam pump.

Denys Papin, the pupil and assistant of Huyghens, continued experimenting upon the production of motive power, and in 1690 published a description of his attempts at Leipzig, entitled "A New Method of Securing Cheaply Motive Power of Considerable Magnitude."

He mentions the gunpowder engine, and states that "until now all experiments have been unsuccessful; and after the combustion of the exploded powder there always remains in the cylinder one-fifth of its volume of air."

For the explosion of the gunpowder he substituted the generation and condensation of steam, heating the bottom of his cylinder by a fire; a small quantity of water contained in it was vaporized, and then on removing the fire the steam condensed and the piston was forced down. This was substantially the Newcomen steam engine, but without the separate boiler.

Papin died about the year 1710, a disappointed man, about the same time as Newcomen. Thomas Newcomen, ironmonger and blacksmith, of Dartmouth, England, had first succeeded in getting his engine to work. The hard fight to wrest from nature a manageable motive power and to harness fire for industrial use was continued by this clever blacksmith, and he succeeded when the more profound but less constructively skillful philosophers had failed.

The success of the steam method and the fight necessary to perfect it to the utmost absorbed the energy of most able engineers—Beighton, John Smeaton—accomplishing much in applying and perfecting it before the appearance of James Watt upon the scene.

It is interesting to note that in England alone over 2,000 horse power of Newcomen engines were at work before Watt commenced his series of magnificent inventions; he commenced experimenting on a Newcomen engine model in 1759 at Glasgow University, and in 1774 came to Birmingham, entered into partnership with Boulton, and 1781 we find his beautiful double acting beam condensing engine in successful work.

From that time until now the steam engine has steadily advanced, increasing in economy of fuel from 10 lb. of coal per horse power per hour to about 1¾ lb. per horse power per hour, which is the best result of to-day's steam engine practice. This result, according to the highest authorities, is so near to the theoretical result possible from a steam engine that further improvement cannot now be looked for. Simultaneously with the development of the steam engine, inventors continued to struggle with the direct acting combustion or gas engine, often without any definite understanding of why they should attempt such apparent impossibilities, but always by their experiments and repeated failures increasing knowledge, and forming a firm road upon which those following them traveled to success.

In 1791 John Barber obtained a patent for an engine producing inflammable gas, mixing it with air, igniting it, and allowing the current so produced to impinge upon a reaction wheel, producing motion similar to the well known Aelopile, which I have at work upon the table. About this time, Murdoch (Jas. Watt's assistant at Birmingham) was busy introducing coal gas into use for lighting; in 1792 Boulton and Watt's works were lighted up with coal gas. From this time many gas engines were proposed, and the more impracticable combustion of gunpowder received less attention.

In 1794 Thomas Mead obtained a patent for an engine using the internal combustion of gas; the description is not a clear one, his ideas seem confused.

In the same year Robert Street obtained a patent for an engine which is not unlike some now in use. The bottom of a cylinder, containing a piston, is heated by a fire, a few drops of spirits of turpentine are introduced and evaporated by the heat, the piston is drawn up, and air entering mixes with the inflammable vapor. A light is applied at a touch hole, and the explosion drives up the piston, which, working on a lever, forces down the piston of a pump for pumping water. Robt. Street adds to his description a note: "The quantity of spirits of tar or turpentine to be made use of is always proportional to the confined space, in general about 10 drops to a cubic foot." This engine is quite a workable one, although the arrangements described are very crude.

The first gas engine that was actually at work for some years; and was applied to a variety of purposes, was Samuel Buren's. His patent was granted in 1823, and in 1826 he built a locomotive carriage with which he made several experimental runs in London; he also propelled a vessel with it upon the Thames, and fitted up a large engine for pumping purposes. A company was formed to introduce his engine, but it proved too wasteful of fuel, and the company went into voluntary liquidation. Like almost all engines of this time, the combustion of gas and air was used to produce a vacuum, the piston being driven by atmospheric pressure.

Buren's locomotive carriage was thus in action three years before the great trial in 1829, from which George Stephenson emerged victorious with his wonderful engine "The Rocket." To those curious in the matter, I may mention that S. Buren's patents are dated 1823, No. 4,874, and 1826, No. 5,350.

From this time on, a continuous series of gas engine patents appear, 20 engines being patented between 1826 and 1860, which is the next date worthy of particular mention.

In this year, 1860, the famous "Lenoir" engine appeared. The use of high pressure steam engines had long been common, and Lenoir's engine was analogous to the high pressure engine, as Buren's was to the condensing engine. It created a very general interest, and many engines were constructed and used in France, England, and America; it resembled very much in external appearance an ordinary high pressure horizontal steam engine, and it was double acting.

During the following six years, other 20 British patents were granted, and the gas engine passed from the state of a troublesome toy to a practicable and widely useful machine.

From 1791 to the end of 1866, in all 46 British patents were granted for gas engines, and in these patents are to be found the principles upon which the gas engines of to-day are constructed, many years elapsing before experience enough was gained to turn the proposals of the older inventors to practical account.

The most important of these patents are:

Leaving for the present the history of the gas engine, which brings us to a stage comparable to the state of the steam engine during the Newcomen's time, it will be advisable to give some consideration to the principles concerned in the economical and efficient working of gas engines, in order to understand the more recent developments.

It has been seen that gunpowder was the explosive used to produce a vacuum in Huyghens' engine, and that it was abandoned in favor of gas by Buren in 1823. The reason of departure is very obvious: a gunpowder explosion and a gaseous explosion differ in very important practical points.

Gunpowder being a solid substance is capable of being packed into a very small space; the gas evolved by its decomposition is so great in volume that, even in the absence of any evolution of heat, a very high pressure would result. One cubic inch of gunpowder confined in a space of one cubic inch would cause a pressure by the gas it contains alone of 15,000 lb. per square inch; if the heating effect be allowed for, pressures of four times that amount, or 60,000 lb. per square inch, are easily accounted for. These pressures are far too high for use in any engine, and the bare possibility of getting such pressure by accident put gunpowder quite outside the purpose of the engineer, quite apart from any question of comparative cost. In a proper mixture of inflammable gas and air is found an exceedingly safe explosive, perfectly manageable and quite incapable of producing pressures in any sense dangerous to a properly constructed engine.

The pressure produced by the explosion of any mixture of gas and air is strictly determined and limited, whereas the pressure produced by the explosion of gunpowder depends greatly upon the relation between the volume of the gunpowder and the space in which it is confined.

Engines of the "Lenoir" type are the simplest in idea and construction; in them a mixture of gas and air is made in the cylinder during the first half of the piston stroke, air being taken from the atmosphere and drawn into the cylinder by the forward movement of the piston. At the same time gas entering by a number of holes, and streaming into the air to form an explosive mixture, the movement of a valve cuts off the supply, and brings the igniting arrangement into action. The pressure produced by the explosion acting upon the piston makes it complete its stroke, when the exhaust valve opens exactly as in the steam engine. The Lenoir and Hugon engines, the earlier forms of this type, were double acting, receiving two impulses for every revolution of the crank, the impulse differing from that in a high pressure steam engine in commencing at half stroke.

The Lenoir igniting arrangement was complicated and troublesome. I have it upon the table; the mixture was ignited at the proper time by the electric spark produced from a primary battery and Ruhmkorff coil.

The Hugon engine was an advance in this respect, using a flame ignited, and securing greater certainty of action in a comparatively simple manner.

It is really a modification of Barnett's lighting cock described in his patent of 1838.

Other difficulties were found in using these engines; the pistons became exceedingly hot. In the case of the Lenoir larger engines, it sometimes became red hot, and caused complete ruin of the cylinder by scoring and cutting up. Hugon to prevent this injected some water.

In the all important question of economy, these engines were found grievously wanting, Lenoir consuming 95 cubic feet per I.H.P. per hour; Hugon consuming 85 cubic feet per I.H.P. per hour.

The surviving engines of this type are only used for very small powers, from one to four man power, or ⅛ to ½ horse, the most widely known of this kind being the "Bischoff," which is very largely used; its consumption of gas is even greater than the Lenoir, being 110 cubic feet per horse power per hour, as tested with a half-horse engine at a late exhibition of gas apparatus at Stockport.

So large a consumption of gas prevented these engines coming into extended use for engines of moderate power, and led inventors to work to obtain better results. The force generated by the explosion of a mixture of gas and air is very short lived, and if it is to be fully utilized must be used quickly; a high pressure is produced, but it very quickly disappears.

The quicker the piston moves after the maximum pressure is reached, the less will be the loss of heat to the sides of the cylinder. The flame which fills the cylinder and causes the increase of pressure rapidly loses heat, and the pressure falls.

The idea of using a free piston was proposed as a remedy; it was thought that a piston connected to a crank in the ordinary manner could not move fast enough to utilize the pressure before it was lost. Many inventors proposed to perform work upon a piston free from any direct connection with the crank or shaft of the engine; the explosion after attaining its maximum pressure expends its force in giving velocity to a piston; the velocity so acquired carries it on against atmospheric pressure until the energy is all absorbed, and a vacuum or deficit of pressure exists in the cylinder instead of an excess of pressure. The return stroke is accomplished by the atmospheric pressure, and the work is now done upon the engine shaft on the return only. The method of connecting on the return stroke while leaving the piston free on the out stroke varies, but in many engines the principle was the same.

Barsante and Matteucci, year 1857, British patent No. 1,625, describe the first engine of this kind, but Messrs. Otto and Langen were the first to successfully overcome all difficulties and make a marketable engine of it. Their patent was dated 1866, No. 434. To distinguish it from Otto's later patents, it may be called the rack and clutch engine.

The economy obtained by this engine was a great advance upon the Lenoir. According to a test by Prof. Tresca, at the Paris Exhibition of 1867, the gas consumed was 44 cubic feet per indicated horse power per hour. According to tests I have made myself in Manchester with a two horse power engine, Otto and Langen's free piston engine consumes 40 cubic feet per I.H.P. per hour. This is less than one-half of the gas used by the Hugon engine for one horse power.

The igniting arrangement is a very good modification of Barnett's lighting cock, which I have explained already, but a slide valve is used instead of a cock.

Other engines carried out the same principle in a different manner, including Gilles' engine, but they were not commercially so successful as the Otto and Langen. Mr. F.H. Wenham's engine was of this type, and was working in England, Mr. Wenham informed me, in 1866, his patent being taken out in 1864.

The great objection to this kind of engine is the irregularity and great noise in working; this was so great as to prevent engines from being made larger than three horse power. The engine, however, did good work, and was largely used from 1866 until the end of 1876, when Mr. Otto produced his famous engine, now known as "The Otto Silent Gas Engine." In this engine great economy is attained without the objectionable free piston by a method proposed first by Burnett, 1838, and also by a Frenchman, Millein, in 1861; this method is compression before ignition. Other inventors also described very clearly the advantages to be expected from compression, but none were able to make it commercially successful till Mr. Otto. To him belongs the great credit of inventing a cycle of operations capable of realizing compression in a simple manner.

Starting from the same point as inventors did to produce the free piston engine—namely, that the more quickly the explosive force is utilized, the less will be the loss, and the greater the power produced from a quantity of burning gas—it is evident that if any method can be discovered to increase the pressure upon the piston without increasing the temperature of the flame causing this pressure, then a great gain will result, and the engine will convert more of the heat given to it into work. This is exactly what is done by compression before ignition. Suppose we take a mixture of gas and air of such proportions as to cause when exploded, or rather ignited (because explosion is too strong a term), a pressure of 45 lb. above atmosphere, or 60 lb. per square inch absolute pressure. Then this mixture, if compressed to half volume before igniting and kept at constant temperature, would give, when ignited, a pressure of 120 lb. total, or 105 lb. above atmosphere, and this without any increase of the temperature of the flame.

The effect of compression is to make a small piston do the work of a large one, and convert more heat into work by lessening the loss of heat through the walls of the cylinder. In addition to this advantage, greater expansions are made possible, and therefore greatly increase economy.

The Otto engine must be so familiar in appearance to all of you, that I need hardly trouble you with details of its external appearance. I shall briefly describe its action. Its strong points and its weak points are alike caused by its cycle. One cylinder and piston suffices to carry out its whole action. Its cycle is: First outstroke, gas and air sucked into the cylinder; first instroke, gas and air compressed into space; second outstroke, impulse due to ignition; second instroke, discharge of exhausted gases. When working at full power, it gets one impulse for every two revolutions; this seems to be a retrograde movement, but, notwithstanding, the advantages obtained are very great. The igniting arrangement is in the main similar to that used on the rack and clutch engine. The engine has been exceedingly successful, and is very economical. The Otto compression engine consumes 21 cubic feet of gas per I.H.P. per hour, and runs with great smoothness.

In 1876 I commenced my work upon gas engines, and very soon concluded that the compression system was the true line to proceed upon. It took me two years to produce a workable engine. My efforts have always been directed toward producing an engine giving at least one impulse every revolution and, if possible, to start without hand labor, just as a steam engine does. My first gas engine was running in 1878, and patented and exhibited in 1879. It was first exhibited at the Kilburn Royal Agricultural Society's show.

This engine was self-starting, gave an ignition at every revolution, and ignited without external flame. It consisted of two cylinders, a motor, and a compressing pump, with a small intermediate reservoir. Suitable valves introduced the mixture of gas and air into the pump, and passed it when compressed from the reservoir to the motor cylinder. The igniting arrangement consisted of a platinum cage firmly fixed in a valve port; this cage was heated in the first instance by a flame of gas and air mixed; it became white hot in a few seconds, and then the engine was started by opening a valve.

The platinum was kept hot by the heat derived from the successive ignitions, and, the engine once started, no further external flame was required. I have here one of these platinum cages which has been in use. Finding this method not well suited for small engines, I produced the engine which is at present in the market under my name.

The cycle is different, and is designed for greater simplicity and the avoidance of back ignitions. It also consists of two cylinders, motor cylinder and the displace or charging cylinder. There is no intermediate reservoir. The displace crank leads the motor by a right angle, and takes into it the mixed charge of gas and air, in some cases taking air alone during the latter part of its stroke.

The motor on the outstroke crosses V-shaped parts about from one-sixth to one-seventh from the out end, the displacer charge now passing into the motor cylinder, displacing the exhaust gases by these ports and filling the cylinder and the space at the end of it with the explosive mixture. The introduction of some air in advance of the charge serves the double purpose of cooling down the exhaust gases and preventing direct contact of the inflammable mixture with flame which may linger in the cylinder from the previous stroke. The instroke of the motor compresses the charge into the conical space at the end of the cylinder, and, when fully compressed, ignition is effected by means of the slide I have upon the table.

This system of ignition has been found very reliable, and capable of acting as often as 400 times per minute, which the Otto ignite is quite incapable of doing. By this cycle the advantages of compression are gained and one step nearer to the steam engine is attained, that is, an impulse is given for every revolution of the engine.

As a consequence, I am able with my engine to give a greater amount of power for a comparatively small weight. In addition to this, I have introduced a method of self-starting; in this I believe I was the first—about 100 of my engines are now using self-starting.

The largest single engine I have yet made indicates 30 H.P. The consumption of gas in Glasgow is: Clerk engine consumes in Glasgow 18 cubic feet per I.H.P. per hour; Clerk engine consumes in Manchester 22 cubic feet per I.H.P. per hour. So far as I know, the Otto engine and my own are the only compression engines which have as yet made any success in the market. Other engines are being continually prepared, gas engine patents being taken out just now at the rate of 60 per annum, but none of them have been able as yet to get beyond the experimental stage. The reason is simply the great experience necessary to produce these machines, which seem so very simple; but to the inexperienced inventor the subject fairly bristles with pitfalls.

I have here sections of some of the earlier engines, including Dr. Siemens' and Messrs. Simon and Beechy. Although interesting and containing many good points, these have not been practically successful.

The Simon engine is an adaptation of the well-known American petroleum motor, the Brayton, the only difference consisting in the use of steam as well as flame.

Dr. Siemens worked for some twenty years on gas engines, but he aimed rather high at first to attain even moderate success. Had he lived, I doubt not but that he would have succeeded in introducing them for large powers. In 1882 he informed me that he had in hand a set of gas engines of some hundreds of horse power for use on board ship, to be supplied with gas from one of his gas producers modified to suit the altered conditions.

Summarizing the ground over which we have passed, we find the origin of the gas engine in the minds of the same men as were first to propose the steam engine, Huyghens and Papin, 1680 and 1690. Greater mechanical difficulties and ignorance of the nature of explosives caused the abandonment of the internal combustion idea, and the mechanical difficulties with steam being less, the steam engine became successful, and triumphed over its rival. The knowledge and skill gained in the construction of steam engines made it possible once again to attack the more difficult problem, and simultaneously with the introduction and perfecting of the steam engine, the gas engine idea became more and more possible, the practicable stage commencing with Lenoir and continuing with Hugon, Millein, Otto and Langen, F.H. Wenham, then Otto and Clerk. In 1860, 95 cubic feet of gas produced one horse power for an hour; in 1867, 40 cubic feet accomplished the same thing; and now (1885) we can get one horse power for an hour for from 15 to 20 cubic feet of gas, depending on the size of the engine used.

Considered as a heat engine, the gas engine is now twice as efficient as the very best modern steam engine. It is true the fuel used at present is more expensive than coal, and for large powers the steam engine is the best because of this. But the way is clearing to change this. Gas engines as at present, if supplied with producer gas, produced direct from coal without leaving any coke, as is done in the Siemens, the Wilson, and the Dawson producers, will give power at one-half the cost of steam power. They will use ⅞ of a pound of coal per horse power per hour, instead of 1¾ lb., as is done in the best steam engines. The only producer that makes gas for gas engines at present is the Dawson, and in it anthracite is used, because of the difficulty of getting rid of the tar coming from the Siemens and Wilson producers, using any ordinary slack.

When this difficulty has been overcome, and that it will be overcome there can be no manner of doubt, gas engines will rapidly displace the steam engine, because a gas engine with a gas producer, producing gas from any ordinary coal with the same ease as steam is produced from a boiler, will be much safer, and will use one-half the fuel of the very best steam engines for equal power. The first cost also will not be greater than that of steam. The engine itself will be more expensive than a steam engine of equal power, but the gas producer will be less expensive than the boiler at present. Perfect as the gas engine now is, considered as a machine for converting heat into work, the possibility of great development is not yet exhausted. Its economy may be increased two or even three fold; in this lies the brilliant future before it. The steam engine is nearly as perfect as it can be made; it approaches very nearly the possibility of its theory. Its defect does not lie in its mechanism, but in the very properties of water and steam itself. The loss of heat which takes place in converting liquid water into gaseous steam is so great that by far the greater portion of the heat given out by the fuel passes away either in the condenser or the exhaust of a steam engine; but a small proportion of the heat is converted into work.

The very best steam engines convert about 11 per cent. of the heat given them into useful work, the remaining 89 per cent. being wasted, principally in the exhaust of the engine.

Gas engines now convert 20 per cent. of the heat given to them into work, and very probably will, in a few years more, convert 60 per cent. into useful work. The conclusion, then, is irresistible that, when engineers have gained greater experience with gas engines and gas producers, they will displace steam engines entirely for every use—mills, locomotives, and ships.

[1]

Lecture by Mr. Dugald Clerk, before the Literary and Philosophical Society, Oldham.

RAPID CONSTRUCTION OF THE CANADIAN PACIFIC RAILWAY.

By E.T. ABBOTT, Member of the Engineers' Club of Minnesota. Read December 12, 1884.

During the winter of 1881 and 1882, the contract was let to Messrs. Langdon, Sheppard & Co., of Minneapolis, to construct during the working season of the latter year, or prior to January 1, 1883, 500 miles of railroad on the western extension of the above company; the contract being for the grading, bridging, track-laying, and surfacing, also including the laying of the necessary depot sidings and their grading. The idea that any such amount of road could be built in that country in that time was looked upon by the writer hereof, as well as by railroad men generally, as a huge joke, perpetrated to gull the Canadians. At the time the contract was let, the Canadian Pacific Railway was in operation to Brandon, the crossing of the Assiniboine River, 132 miles west of Winnipeg. The track was laid, however, to a point about 50 miles west of this, and the grading done generally in an unfinished state for thirty miles further. This was the condition of things when the contract was entered into to build 500 miles—the east end of the 500-mile contract being at Station 4,660 (Station 0 being at Brandon) and extending west to a few miles beyond the Saskatchewan River.

The spring of 1882 opened in the most unpromising manner for railroad operations, being the wettest ever known in that country. Traffic over the St. Paul, Minneapolis & Manitoba Railroad, between St. Paul and Winnipeg, was entirely suspended from April 15 to the 28th, owing to the floods on the Red River at St. Vincent and Emerson, a serious blow to an early start, as on this single track depended the transportation of all supplies, men, timber, and contractors' plant, together with all track materials (except ties), all of these things having to come from or through St. Paul and Minneapolis. The writer hereof was appointed a division engineer, and reported at Winnipeg the 15th of April, getting through on the last train before the St. Vincent flood. No sooner was the line open from St. Paul to Winnipeg than the cotillon opened between Winnipeg and Brandon, with a succession of washouts that defied and defeated all efforts to get trains over, so it was not until the fifth day of May that I left Winnipeg to take charge of the second division of 30 miles.

By extremely "dizzy" speed I was landed at the end of the track, 180 miles from Winnipeg, on the evening of the 9th (4 days). My outfit consisted of three assistant engineers and the necessary paraphernalia for three complete camps, 30 days' provisions (which turned out to be about 20), 11 carts and ponies, the latter being extremely poor after a winter's diet on buffalo grass and no grain. On the 18th day of May I had my division organized and camps in running order. The country was literally under water, dry ground being the exception, and I look upon the feat of getting across the country at all as the engineering triumph of my life.

On May 20 a genuine blizzard set in, lasting 24 hours, snowed five inches, and froze the sloughs over with half an inch of ice, a decidedly interesting event to the writer, as he was 18 miles from the nearest wood, therefore lay in his blankets and ate hard tack. I stabled my ponies in the cook tent, and after they had literally eaten of the sod inside the tent, I divided my floor with them.

On 28th day of May I saw the first contractor, who broke ground at station 7,150. On the 1st of June I was relieved from this division, and ordered to take the next, 50 miles west. On the 13th day of June ground was broken on this division, at station 8,070, or only about 62 miles west of the east end of the 500-mile contract. It looked at this time as though they might build 150 miles, but not more. But from this time on very rapid progress was made. On July 17 the track reached station 7,000, making however up to this time but about 50 miles of track-laying, including that laid on the old grade; but large forces were put on to surfacing, and the track already laid was put in excellent condition for getting material to the front. The weather from this until the freezing-up was all that could be desired. Work ceased about the 1st of January, 1883, for the season, and the final estimate for the work was as follows: 6,103,986 cubic yards earth excavation, 2,395,750 feet B.M. timber in bridges and the culverts, 85,708 lineal feet piling, 435 miles of track-laying. This work was all done in 182 working days, including stormy ones, when little, if anything, could be done, making a daily average of 33,548 yards excavation, 13,150 feet B.M. timber, 471 feet piling, 2-38/100 miles track-laying. We never had an accurate force report made of the whole line, but roughly there were employed 5,000 men and 1,700 teams.

The admirable organization of the contractors was something wonderful. The grading work was practically all done by sub-contractors, Messrs. Langdon, Sheppard & Co. confining themselves to putting in the supplies and doing the bridge work, surfacing, and track-laying. The grading forces were scattered along about 150 miles ahead of the track and supply stores, established about 50 miles apart, and in no case were sub-contractors expected to haul supplies over 100 miles. If I remember rightly, there were four trains of about forty wagons each, hauling supplies from the end of track to the stores.

As can be readily seen, the vital point of the whole work, and the problem to solve, was food for men and horses. 1,700 bushels of oats every day and 15,000 pounds of provisions, Sundays and all, for an entire season, which at the beginning of the work had to come about 170 miles by rail, and then be taken from 50 to 150 miles by teams across a wilderness, is on the face of it considerable of an undertaking, to say nothing about hauling the pile-drivers, piles, and bridge-timber there. To keep from delaying the track, sidings 1,500 feet long were graded, about 7 miles apart. A side-track crew, together with an engine, four flats, and caboose, were always in readiness; and as soon as a siding was reached, in five hours the switches would be in, and the next day it would be surfaced and all in working order, when the operating department would fill it with track material and supplies. From the head of the siding to the end of the track the ground was in hands of track-laying engine, never going back of the last siding for supplies or material, and my recollection is that there were but six hours' delay to the track from lack of material the whole season, at any rate up to some time in November. The track-laying crew was equal to 4 miles per day, and in the month of August 92 miles of track were laid. The ties were cut on the line of the road about 100 miles east of Winnipeg, so the shortest distance any ties were hauled was 270 miles; the actual daily burden of the single track from Winnipeg west was 24 cars steel, 24 cars ties, aside from the transportation of grain and provisions, bridge material, and lumber for station houses. The station buildings were kept right up by the company itself, and a depot built with rooms for the agent every 15 miles, or at every second siding. The importance of keeping the buildings up with the track was impressed on the mind of the superintendent of this branch, and, as a satire, he telegraphed asking permission to haul his stuff ahead of the track by teams, he being on the track-layers' heels with his stations and tanks the whole season. The telegraph line was also built, and kept right up to the end of the track, three or four miles being the furthest they were at any time behind.

It might be supposed that work done so rapidly would not be well done, but it is the best built prairie road I know of on this continent. It is built almost entirely free from cuts, and the work is at least 20 per cent. heavier than would ordinarily be made across the same country in the States, on account of snow. 2,640 ties were laid to the mile, and the track ballasting kept well up with the laying; so well, in fact, and so well done, that as 100 mile sections were completed schedule trains were put on 20 miles an hour, and the operating department had nothing to do but make a time table; the road was built by the construction department before the operating department was asked to take it. The engineering was organized in divisions of 30 miles each, and as each was finished the parties moved ahead again to the front, the engineers usually finding men sitting on their shovels waiting for the work to be laid out for them. It was as much as the locating parties could do to keep out of the way of the construction. The roadbed was built 14 ft. wide in embankment and 20 in the very few cuts there were, there being no cuts of any moment except through the Coteaus and the Saskatchewan crossing, and these have since been widened out on account of snow, so that the road can be operated the year round and the bucking-snow account cut no figure in the operating expenses.

The country is a virgin desert. From Winnipeg to the Pacific Ocean there are a few places that might attain to the dignity of an oasis—at Brandon, Portage la Prairie, etc.—but it is generally what I should call worthless; 100 miles to wood and 100 feet to water was the general experience west of the Moose jaw, and the months of June, July, and August are the only three in the year that it is safe to bet you will not have sleighing. I burned wood and used stakes that were hauled by carts 85 miles, and none any nearer. It is a matter of some pride that both the engineering and the construction were done by what our Canadian neighbors kindly termed "Yankee importations." However, there was one thing that in the building of this road was in marked contrast to any other Pacific road ever constructed, that is, there was no lawlessness, no whisky, and not even a knock-down fight that I ever heard of the whole season, and even in the midst of 12,000 Indians, all armed with Winchester rifles and plenty of ammunition, not one of the locating or construction parties ever had a military escort, nor were any depredations ever committed, except the running off of a few horses, which were usually recovered; and I think there were but two fatal accidents during the season, one man killed on the Grand Coule Bridge, and another from being kicked by a horse.

The track was all laid from one end, and in no case were rails hauled ahead by teams. Two iron cars were used, the empty returning one being turned up beside the track to let the loaded one by.

The feat in rapid construction accomplished by this company will never be duplicated, done as it was by a reckless expenditure of money, the orders to the engineers being to get there regardless of expense and horse-flesh; if you killed a horse by hard driving, his harness would fit another, and there was no scrutiny bestowed on vouchers when the work was done; and I must pay the tribute to the company to say that everything that money would buy was sent to make the engineers comfortable. It was bad enough at best, and the Chief Engineer (J.C. James) rightly considered that any expense bestowed on the engineering part of the work was a good investment.

THE OSGOOD MAMMOTH EXCAVATOR.

In the accompanying illustration, we present to our readers a mammoth excavator, built by the Osgood Dredge Company of Albany, N.Y., for the Pacific Guano Company of California, for uncovering their phosphate deposits on Chisholm Island, South Colombia.

THE OSGOOD MAMMOTH EXCAVATOR.

In order to bring out more clearly the principal problem involved in the construction of this machine, we shall state first the proposed method of its operation. This is as follows, viz.: The excavator is to dig a trench thirty feet wide, down to the phosphate rock, and the entire length of the bed—about one quarter of a mile—dumping the earth of the first cut to one side. The phosphate is taken out behind the excavator. On reaching the end of the bed, the excavator is reversed and starts back, making a second cut thirty feet wide, and dumping now into the cut from which the phosphate has just been removed. In this way the entire bed is traversed, the excavator turning over the earth in great furrows thirty feet wide, and giving an opportunity to simultaneously get out all the phosphate.

As will be seen, the main problem presented was to turn the car around at each end of the cut in a very limited space. To accomplish this, the car is mounted on a fixed axle at each end and on a truck under its center of gravity; this is somewhat forward of the geometrical center of the car. The frame of the truck is circular, thirteen feet in diameter, made of I beams curved to shape. The circle carries a track, on which a ring of coned rollers revolves, which in turn supports the car. By pulling out the track from under both ends of the car, the whole weight is balanced on this central turntable truck, thus admitting of the car being turned, end for end, within its own length. This method of turning the car, and the size of the machine, are the principal features.

The car is 40' × 13', with arched truss sides. The track is seven feet gauge, the spread between tracks 20 feet, the height of the A frame 38 feet, length of boom 40 feet, swinging in a circle of 30 feet radius, and through two-thirds of the entire circle. It has a steel dipper of 46 cubic feet capacity, 1 inch steel chains, 10" × 12" double cylinder hoisting engine, and 6¼" × 8" double cylinder reversible crowding engine. The drums are fitted with friction clutches. Owing to the great distance at which the dipper is handled, its size is reduced, and because it swings on the arc of so large a circle the capacity of this machine is only one-half of that of the No. 1 excavator built by the Osgood Dredge Company. Nevertheless it will do the work of from 75 to 100 men, since its capacity is from 800 to 1,000 cubic yards per day, the amount of rock uncovered depending, of course, upon the depth of earth overlying it. The excavator will dump 30 feet from the center line of the car, and 26 feet above the track, which is laid on the rock. Total weight about fifty tons. The crew required for its operation consists of 1 engineer, 1 fireman, 1 craneman, and 4 to 5 pit men to tend jacks, move track, etc.

In the illustration the boiler connections are omitted, also the housing for the protection of the crew. The design is characterized by the evident care which has been bestowed upon securing simplicity and durability.—American Engineer.

THE OSGOOD EXCAVATOR.

At a recent meeting of the Engineers' Club of Philadelphia, Mr. John C. Trautwine, Jr., exhibited and described drawings of a large land dredge built by the Osgood Dredge Co., of Albany, New York, for the Pacific Guano Co., to be used in removing 8 to 15 feet of material from the phosphate rock at Bull River, S.C.

The more prominent features of the machine are the car-body, the water tank, boiler and engine, the A frame (so-called from its slight resemblance to the letter A), the boom, the dipper-handle; and the dipper, drawings of which were shown and described in detail.

Before the excavation is begun, the forward end of the car (the end nearest the dipper) is lifted clear of the track by means of 3 screw-jacks. When the machine has excavated as far in advance of itself as the length of the boom and that of the dipper-handle will permit, say about 8 feet, the car is again lowered to the track, the screw-jacks removed, and the car is moved forward about 8 feet by winding the rope upon the drum, the other end of the rope being attached to any suitable fixed object near the line of the track. The forward end of the car is then again lifted by means of the 3 screw-jacks, and the digging is resumed. The machine cuts a channel from 25 to 35 feet wide, and deposits all the dirt upon one side. If necessary, it can dump earth about 25 feet above the track. The miners follow in the wake of the machine, getting out the phosphate as fast as it is uncovered. When the machine reaches the end of the field it is lowered to the track and the screw-jacks are removed. Shoes or skids are then placed upon the track, and the wheels of the turntable are run up on them. This lifts the end wheels clear of the track, so that the car and machine rest entirely upon the turntable. By now blocking the turntable wheels and winding up only one of the ropes, the car body and the machine are swung around end for end. The digging is then resumed in the opposite direction, the temporary track, upon which the machine travels, being shifted to one side, so that the second channel is made alongside of the first. The earth removed in cutting this second channel is dumped into the first channel, the phosphate (as stated above) having been first removed.

The dipper is of plate steel, and holds 1¾ cubic yards of earth when even full.

The machine is manned by an engineer, a fireman, and a dipper-tender, besides which from five to ten laborers are required. These look after the track, etc.

CAPSTAN NAVIGATION ON THE VOLGA.

On several of the large rivers on the Continent, with rapid currents, cable towage has been introduced in addition to the older methods of transporting merchandise by sailing and steam boats or by towage with screw or paddle tugs. A chain or wire rope is laid on the bottom of the river bed, fixed to anchors at the ends and passed over a chain pulley driven by the steam engine and guided by pulleys on the steam tug, the tug lifting it out of the water at the bow and dropping it over the stern and winding itself with the barges attached to it along the chain, the latter being utilized as a rule only for the up journey, while down the river the tugs are propelled by paddles or screws, and can tow a sufficient number of barges with the assistance of the current. The system has been found advantageous, as, although the power required for drawing the barges and tugs against the current is of course the same in all cases, the slip and waste of power by screws and paddles is avoided. The size of the screws or paddles is also limited by the nature of the river and its traffic, and with cable towage a larger number of barges can be hauled, while the progress made is definite and there is no drifting back, as occurs with paddle or screw tugs when they have temporarily to slow or stop their engines on account of passing vessels. Several streams, as the Elbe, Rhine, and Rhone, have now such cables laid for long distances in those parts of the rivers where the traffic is sufficient to warrant the adoption of the system. While this has been introduced only during the last 16 or 18 years, a similar method of transporting merchandise has been in use in Russia on the river Volga for upward of 40 years. Navigation on this river is interrupted for about half the year by the ice, and the traffic is of larger amount only during part of the summer, while the length of the river itself is very great, so that laying down permanent cables would not pay; while, on the other hand, the current is so strong that towage of some sort must be resorted to for the transport of large quantities. The problem has been solved by the introduction of the capstan navigation or towage.

CAPSTAN NAVIGATION ON THE VOLGA.

There are two kinds of capstans in use, one actuated by horse-power and the other by steam engines. A horse capstan boat carries according to size 150 to 200 horses, which are stabled in the hold. On deck a number of horse gears are arranged at which the horses work. The power of the separate gears is transmitted to a main shaft, which is connected to the drums that wind on the rope. The horses work under an awning to protect them from the burning sunshine, and are changed every three hours. Eight and sometimes ten horses work at each horse gear. The horses are changed without interruption of the work, the gears being disengaged from the main shaft in rotation and the horses taken out and put in while the gear is standing. The horses are bought at the place of departure in the south of Russia and resold at the destination, usually Nishny-Novgorod, at a fair profit, the capstan boat carrying fodder and provender for the attendants. The capstan is accompanied by a steam launch which carries the anchor and hawser forward in advance of the capstan. The latter has a diameter of as much as 5 in., and is two to three miles in length. The anchor is dropped by the tug and the hawser carried back to the capstan, where it is attached to one of the rope drums, and the boat with the barges attached to it towed along by the horse gears described above winding on the hawser. The advance continues without interruption day and night, the launch taking a second anchor and hawser forward and dropping the anchor in advance of the first by a hawser's length, so that when the capstan has wound up the first hawser it finds a second one ready for attachment to the rope drum. The launch receives the first hawser, picks up the anchor, and passes the capstan to drop it again in advance of the anchor previously placed, and carries the hawser back to the capstan, and so on. A capstan tows twelve or more barges, placed in twos or threes beside and close behind each other, with a load of a million pounds, or about 16,000 to 17,000 tons. From Astrachan and the mouth of the Kama the capstans make during the season from the beginning of May to the end of July in the most favorable case two journeys to the fair of Nishny-Novgorod; after this time no more journeys are made, as the freights are wanting. At the end of the up-stream journey the horses are sold, as mentioned before, and the capstan towed down stream by the steam launch to Astrachan or the Kama mouth, where meanwhile a fresh lot of barges has been loaded and got ready, a new supply of horses is bought, and the operation repeated.

Besides these horse capstans there are steam capstans which are less complicated and have condensing steam engines of about 100 horse power, the power being transmitted by gearing to the rope drum. The rope drum shaft projects on both sides beyond the boards of the boat, and for the return journey paddle wheels, are put on to assist the launch in towing the clumsy and big capstan boat down the river. The steam capstans tow considerably larger masses of goods than the horse capstans and also travel somewhat quicker, so that the launch has scarcely sufficient time to drop and raise the anchors and also to make double the journey. We do not doubt that this system of towage might with suitable modifications be advantageously employed on the large rivers in America and elsewhere for the slow transport of large quantities of raw materials and other bulky merchandise, a low speed being, as is well known, much more economical than a high speed, as many of the resistances increase as the square and even higher powers of the velocity.

STEAMBOAT EQUIPMENT OF WAR VESSELS.

The larger ships in the navy, and some of the more recent small ones, such as the new cruisers of the Phaeton class, are fitted with powerful steam winches of a type made by Messrs. Belliss and Co. These are used for lifting the pinnaces and torpedo boats.

We give an illustration of one of these winches. The cylinders are 6 in. in diameter and 10 in. stroke. The barrel is grooved for wire rope, and is safe to raise the second class steel torpedo boats, weighing nearly 12 tons as lifted. The worm gearing is very carefully cut, so that the work can be done quietly and safely. With machinery of this kind a boat is soon put into the water, and as an arrangement is fitted for filling the boat's boilers with hot water from the ship's boilers, the small craft can be under way in a very short time from the order being given.

Mr. White is fitting compound engines with outside condensers to boats as small as 21 ft. long, and we give a view of a pair of compound engines of a new design, which Messrs. Belliss are making for the boats of this class. The cylinders are 4 in. and 7 in. in diameter by 5 in. stroke. The general arrangement is well shown in the engraving. On a trial recently made, a 25 ft. cutter with this type of engines reached a speed of 7.4 knots.

About three years ago the late Controller of the Navy, Admiral Sir W. Houston Stewart, wished to ascertain the relative consumption of fuel in various classes of small vessels. An order was accordingly sent to Portsmouth, and a series of trials were made. From the official reports of these we extract the information contained in tables F and G, and we think the details cannot fail to be of interest to our readers. The run around the island was made in company with other boats, without stopping, and observations were taken every half hour. The power given out by the engines was fairly constant throughout. The distance covered was 56 knots, and the total amount of fuel consumed, including that required for raising steam, was 1,218 lb. of coal and 84 lb. of wood. The time taken in raising steam to 60 lb. pressure was forty-three minutes. The rate of consumption of fuel is of course not the lowest that could be obtained, as a speed of over 10 knots is higher than that at which the machinery could be worked most economically.

STEAM WINCH FOR HOISTING AND LOWERING PINNACLES AND TORPEDO BOATS.

The trials afterward made to find the best results that could be obtained in fuel consumption were rather spoiled by the roughness of the weather on the day they were made. The same boat was run for 10 miles around the measured mile buoys in Stokes Bay. The following are some of the results recorded:

In connection with this subject it may perhaps be of interest to give particulars of a French and American steam launch; these we extract from the United States official report before mentioned.

The boat is built of wood, and coppered. The engine consists of one non-condensing cylinder, 7½ in. in diameter and 5.9 in. stroke. The boiler has 4.3 square feet of grate surface. The screw is 21⅔ in. in diameter by 43.3 in, pitch. The speed is 7 knots per hour obtained with 245 revolutions per minute, the slip being 19.7 per cent. of the speed.

The United States navy steam cutters built at the Philadelphia navy yard are of the following dimensions:

The engine has a single cylinder 8 in. in diameter and 8 in. stroke of piston. The screw is four bladed, 4 in. long and 31 in. in diameter by 45 in. pitch. The following is the performance at draught of water 2 feet above rabbet of keel:

These boats are of 1870 type, but may be taken as typical of a large number of steam cutters in the United States navy. The naval authorities have, however, been lately engaged in extensive experiments with compound condensing engines in small boats, and the results have proved so conclusively the advantages of the latter system that it will doubtless be largely adopted in future.—Engineer.

[2]

In consequence of the seas breaking over the boat, a large number of diagrams were destroyed, and, on account of the roughness of the weather, cards were only taken with the greatest difficulty. The records of power developed are therefore not put forward as authoritative.

IMPROVED STEAM TRAP.

The illustrations we give represent an expansion trap by Mr. Hyde, and made by Mr. S. Farron, Ashton-under-Lyne. The general appearance of this arrangement is as in Fig. 1 or Fig. 3, the center view, Fig. 2, showing what is the cardinal feature of the trap, viz., that it contains a collector for silt, sand, or sediment which is not, as in most other traps, carried out through the valve with the efflux of water. The escape valve also is made very large, so that while the trap may be made short, or, in other words, the expansion pipe may not be long, a tolerably large area of outlet is obtained with the short lift due to the small movement of the expansion pipe.

IMPROVED STEAM TRAP.

The object of a steam trap is for the removal of water of condensation without allowing the escape of steam from drying apparatus and steam pipes used for heating, power, or other purposes. One of the plans employed is by an expansion pipe having a valve fixed to its end, so that when the pipe shortens from being cooler, due to the presence of the water, the valve opens and allows the escape of the water until the steam comes to the trap, which, being hotter, lengthens the pipe and closes the valve. Now with this kind of trap, and, in fact, with any variety of trap, we understand that it has been frequently the experience of the user to find his contrivance inoperative because the silt or sand that may be present in the pipes has been carried to the valve and lodged there by the water, causing it to stick, and with expansion traps not to close properly or to work abnormally some way or other. The putting of these contrivances to rights involves a certain amount of trouble, which is completely obviated by the arrangement shown in the annexed engravings, which is certainly a simple, strong, and substantial article. The foot of the trap is made of cast iron, the seat of the valve being of gun metal, let into the diaphragm, cast inside the hollow cylinder. The valve, D, is also of gun metal, and passing to outside through a stuffing box is connected to the central expansion pipe by a nut at E. The valve is set by two brass nuts at the top, so as to be just tight when steam hot; if, then, from the presence of water the trap is cooled, the pipe contracts and the water escapes. A mud door is provided, by which the mud can be removed as required. The silt or dirt that may be in the pipes is carried to the trap by the water, and is deposited in the cavity, as shown, the water rises, and when the valve, D, opens escapes at the pipe, F, and may be allowed to run to waste. A pipe is not shown attached to F, but needless to say one may be connected and led anywhere, provided the steam pressure is sufficient. For this purpose the stuffing-box is provided; it is really not required if the water runs to waste, as is represented in the engraving. To give our readers some idea of the dimensions of the valve, we may say that the smallest size of trap has 1 in. expansion pipe and a valve 3 in. diameter, the next size 1¼ in. expansion pipe and a valve 4½ in. diameter, and the largest size has a pipe 1½ in. and a valve 6 in. diameter. Altogether, the contrivance has some important practical advantages to recommend it.—Mech. World.

CRITICAL METHODS OF DETECTING ERRORS IN PLANE SURFACES.[^[3]]

By JOHN A. BRASHEAR.

In our study of the exact methods of measurement in use to-day, in the various branches of scientific investigation, we should not forget that it has been a plant of very slow growth, and it is interesting indeed to glance along the pathway of the past to see how step by step our micron of to-day has been evolved from the cubit, the hand's breadth, the span, and, if you please, the barleycorn of our schoolboy days. It would also be a pleasant task to investigate the properties of the gnomon of the Chinese, Egyptians, and Peruvians, the scarphie of Eratosthenes, the astrolabe of Hipparchus, the parallactic rules of Ptolemy, Regimontanus Purbach, and Walther, the sextants and quadrants of Tycho Brahe, and the modifications of these various instruments, the invention and use of which, from century to century, bringing us at last to the telescopic age, or the days of Lippershay, Jannsen, and Galileo.

FIG. 1.

It would also be a most pleasant task to follow the evolution of our subject in the new era of investigation ushered in by the invention of that marvelous instrument, the telescope, followed closely by the work of Kepler, Scheiner, Cassini, Huyghens, Newton, Digges, Nonius, Vernier, Hall, Dollond, Herschel, Short, Bird, Ramsden, Troughton, Smeaton, Fraunhofer, and a host of others, each of whom has contributed a noble share in the elimination of sources of error, until to-day we are satisfied only with units of measurement of the most exact and refined nature. Although it would be pleasant to review the work of these past masters, it is beyond the scope of the present paper, and even now I can only hope to call your attention to one phase of this important subject. For a number of years I have been practically interested in the subject of the production of plane and curved surfaces particularly for optical purposes, i.e., in the production of such surfaces free if possible from all traces of error, and it will be pleasant to me if I shall be able to add to the interest of this association by giving you some of my own practical experience; and may I trust that it will be an incentive to all engaged in kindred work to do that work well?

FIG. 2.

In the production of a perfectly plane surface, there are many difficulties to contend with, and it will not be possible in the limits of this paper to discuss the methods of eliminating errors when found; but I must content myself with giving a description of various methods of detecting existing errors in the surfaces that are being worked, whether, for instance, it be an error of concavity, convexity, periodic or local error.

FIG. 3

A very excellent method was devised by the celebrated Rosse, which is frequently used at the present time; and those eminent workers, the Clarks of Cambridge, use a modification of the Rosse method which in their hands is productive of the very highest results. The device is very simple, consisting of a telescope (a, Fig. 1) in which aberrations have been well corrected, so that the focal plane of the objective is as sharp as possible. This telescope is first directed to a distant object, preferably a celestial one, and focused for parallel rays. The surface, b, to be tested is now placed so that the reflected image of the same object, whatever it may be, can be observed by the same telescope. It is evident that if the surface be a true plane, its action upon the beam of light that comes from the object will be simply to change its direction, but not disturb or change it any other way, hence the reflected image of the object should be seen by the telescope, a, without in any way changing the original focus. If, however, the supposed plane surface proves to be convex, the image will not be sharply defined in the telescope until the eyepiece is moved away from the object glass; while if the converse is the case, and the supposed plane is concave, the eyepiece must now be moved toward the objective in order to obtain a sharp image, and the amount of convexity or concavity may be known by the change in the focal plane. If the surface has periodic or irregular errors, no sharp image can be obtained, no matter how much the eyepiece may be moved in or out.

FIG. 4

This test may be made still more delicate by using the observing telescope, a, at as low an angle as possible, thereby bringing out with still greater effect any error that may exist in the surface under examination, and is the plan generally used by Alvan Clark & Sons. Another and very excellent method is that illustrated in Fig. 2, in which a second telescope, b, is introduced. In place of the eyepiece of this second telescope, a diaphragm is introduced in which a number of small holes are drilled, as in Fig. 2, x, or a slit is cut similar to the slit used in a spectroscope as shown at y, same figure. The telescope, a, is now focused very accurately on a celestial or other very distant object, and the focus marked. The object glass of the telescope, b, is now placed against and "square" with the object glass of telescope a, and on looking through telescope a an image of the diaphragm with its holes or the slit is seen. This diaphragm must now be moved until a sharp image is seen in telescope a. The two telescopes are now mounted as in Fig. 2, and the plate to be tested placed in front of the two telescopes as at c. It is evident, as in the former case, that if the surface is a true plane, the reflected image of the holes or slit thrown upon it by the telescope, b, will be seen sharply defined in the telescope, a.

FIG. 5.

If any error of convexity exists in the plate, the focal plane is disturbed, and the eyepiece must be moved out. If the plate is concave, it must be moved in to obtain a sharp image. Irregular errors in the plate or surface will produce a blurred or indistinct image, and, as in the first instance, no amount of focusing will help matters. These methods are both good, but are not satisfactory in the highest degree, and two or three important factors bar the way to the very best results. One is that the aberrations of the telescopes must be perfectly corrected, a very difficult matter of itself, and requiring the highest skill of the optician. Another, the fact that the human eye will accommodate itself to small distances when setting the focus of the observing telescope. I have frequently made experiments to find out how much this accommodation was in my own case, and found it to amount to as much as 1/40 of an inch. This is no doubt partly the fault of the telescopes themselves, but unless the eye is rigorously educated in this work, it is apt to accommodate itself to a small amount, and will invariably do so if there is a preconceived notion or bias in the direction of the accommodation.

FIG. 6.

Talking with Prof. C.A. Young a few months since on this subject, he remarked that he noticed that the eye grew more exact in its demands as it grew older, in regard to the focal point. A third and very serious objection to the second method is caused by diffraction from the edges of the holes or the slit. Let me explain this briefly. When light falls upon a slit, such as we have here, it is turned out of its course; as the slit has two edges, and the light that falls on either side is deflected both right and left, the rays that cross from the right side of the slit toward the left, and from the left side of the slit toward the right, produce interference of the wave lengths, and when perfect interference occurs, dark lines are seen. You can have a very pretty illustration of this by cutting a fine slit in a card and holding it several inches from the eye, when the dark lines caused by a total extinction of the light by interference may be seen.

FIG. 7.

If now you look toward the edge of a gas or lamp flame; you will see a series of colored bands, that bring out the phenomenon of partial interference. This experiment shows the difficulty in obtaining a perfect focus of the holes or the slit in the diaphragm, as the interference fringes are always more or less annoying. Notwithstanding these defects of the two systems I have mentioned, in the hands of the practical workman they are productive of very good results, and very many excellent surfaces have been made by their use, and we are not justified in ignoring them, because they are the stepping stones to lead us on to better ones. In my early work Dr. Draper suggested a very excellent plan for testing a flat surface, which I briefly describe. It is a well known truth that, if an artificial star is placed in the exact center of curvature of a truly spherical mirror, and an eyepiece be used to examine the image close beside the source of light, the star will be sharply defined, and will bear very high magnification. If the eyepiece is now drawn toward the observer, the star disk begins to expand; and if the mirror be a truly spherical one, the expanded disk will be equally illuminated, except the outer edge, which usually shows two or more light and dark rings, due to diffraction, as already explained.

FIG. 8.

Now if we push the eyepiece toward the mirror the same distance on the opposite side of the true focal plane, precisely the same appearance will be noted in the expanded star disk. If we now place our plane surface any where in the path of the rays from the great mirror, we should have identically the same phenomena repeated. Of course it is presumed, and is necessary, that the plane mirror shall be much less in area than the spherical mirror, else the beam of light from the artificial star will be shut off, yet I may here say that any one part of a truly spherical mirror will act just as well as the whole surface, there being of course a loss of light according to the area of the mirror shut off.

This principle is illustrated in Fig. 3, where a is the spherical mirror, b the source of light, c the eyepiece as used when the plane is not interposed, d the plane introduced into the path at an angle of 45° to the central beam, and e the position of eyepiece when used the with the plane. When the plane is not in the way, the converging beam goes back to the eyepiece, c. When the plane, d, is introduced, the beam is turned at a right angle, and if it is a perfect surface, not only does the focal plane remain exactly of the same length, but the expanded star disks, are similar on either side of the focal plane.

FIG. 9.

I might go on to elaborate this method, to show how it may be made still more exact, but as it will come under the discussion of spherical surfaces, I will leave it for the present. Unfortunately for this process, it demands a large truly spherical surface, which is just as difficult of attainment as any form of regular surface. We come now to an instrument that does not depend upon optical means for detecting errors of surface, namely, the spherometer, which as the name would indicate means sphere measure, but it is about as well adapted for plane as it is for spherical work, and Prof. Harkness has been, using one for some time past in determining the errors of the plane mirrors used in the transit of Venus photographic instruments. At the meeting of the American Association of Science in Philadelphia, there was quite a discussion as to the relative merits of the spherometer test and another form which I shall presently mention, Prof. Harkness claiming that he could, by the use of the spherometer, detect errors bordering closely on one five-hundred-thousandth of an inch. Some physicists express doubt on this, but Prof. Harkness has no doubt worked with very sensitive instruments, and over very small areas at one time.

I have not had occasion to use this instrument in my own work, as a more simple, delicate, and efficient method was at my command, but for one measurement of convex surfaces I know of nothing that can take its place. I will briefly describe the method of using it.

FIG. 10.

The usual form of the instrument is shown in Fig. 4; a is a steel screw working in the nut of the stout tripod frame, b; c c c are three legs with carefully prepared points; d is a divided standard to read the whole number of revolutions of the screw, a, the edge of which also serves the purpose of a pointer to read off the division on the top of the milled head, e. Still further refinement may be had by placing a vernier here. To measure a plane or curved surface with this instrument, a perfect plane or perfect spherical surface of known radius must be used to determine the zero point of the division. Taking for granted that we have this standard plate, the spherometer is placed upon it, and the readings of the divided head and indicator, d, noted when the point of the screw, a, just touches the surface, f. Herein, however, lies the great difficulty in using this instrument, i.e., to know the exact instant of contact of the point of screw, a, on the surface, f. Many devices have been added to the spherometer to make it as sensitive as possible, such as the contact level, the electric contact, and the compound lever contact. The latter is probably the best, and is made essentially as in Fig. 5.

FIG. 11.

I am indebted for this plan to Dr. Alfred Mayer. As in the previous figure, a is the screw; this screw is bored out, and a central steel pin turned to fit resting on a shoulder at c. The end of d projects below the screw, a, and the end, e, projects above the milled head, and the knife edge or pivot point rests against the lever, f, which in turn rests against the long lever, g, the point, h, of which moves along the division at j. It is evident that if the point of the pin just touches the plate, no movement of the index lever, g, will be seen; but if any pressure be applied, the lever will move through a multiplied arc, owing to the short fulcri of the two levers. Notwithstanding all these precautions, we must also take into account the flexure of the material, the elasticity of the points of contact, and other idiosyncrasies, and you can readily see that practice alone in an instrument so delicate will bring about the very best results. Dr. Alfred Mayer's method of getting over the great difficulty of knowing when all four points are in contact is quite simple. The standard plate is set on the box, g, Fig. 4, which acts as a resonater. The screw, a, is brought down until it touches the plate. When the pressure of the screw is enough to lift off either or all of the legs, and the plate is gently tapped with the finger, a rattle is heard, which is the tell-tale of imperfect contact of all the points. The screw is now reversed gently and slowly until the moment the rattle ceases, and then the reading is taken. Here the sense of hearing is brought into play. This is also the case when the electric contact is used. This is so arranged that the instant of touching of the point of screw, a, completes the electric circuit, in which an electromagnet of short thick wire is placed. At the moment of contact, or perhaps a little before contact, the bell rings, and the turning of the screw must be instantly stopped. Here are several elements that must be remembered. First, it takes time to set the bell ringing, time for the sound to pass to the ear, time for the sensation to be carried to the brain, time for the brain to send word to the hand to cease turning the screw, and, if you please, it takes time for the hand to stop. You may say, of what use are such refinements? I may reply, what use is there in trying to do anything the very best it can be done? If our investigation of nature's profound mysteries can be partially solved with good instrumental means, what is the result if we have better ones placed in our hands, and what, we ask, if the best are given to the physicist? We have only to compare the telescope of Galileo, the prism of Newton, the pile of Volta, and what was done with them, to the marvelous work of the telescope, spectroscope, and dynamo of to-day. But I must proceed. It will be recognized that in working with the spherometer, only the points in actual contact can be measured at one time, for you may see by Fig. 6 that the four points, a a a a, may all be normal to a true plane, and yet errors of depression, as at e, or elevation, as at b, exist between them, so that the instrument must be used over every available part of the surface if it is to be tested rigorously. As to how exact this method is I cannot say from actual experience, as in my work I have had recourse to other methods that I shall describe. I have already quoted you the words of Prof. Harkness. Dr. Hastings, whose practical as well as theoretical knowledge is of the most critical character, tells me that he considers it quite easy to measure to 1/80000 of an inch with the ordinary form of instrument. Here is a very fine spherometer that Dr. Hastings works with from time to time, and which he calls his standard spherometer. It is delicately made, its screw being 50 to the inch, or more exactly 0.01998 inch, or within 2/100000 of being 1/50 of an inch pitch. The principal screw has a point which is itself an independent screw, that was put in to investigate the errors of the main screw, but it was found that the error of this screw was not as much as the 0.00001 of an inch. The head is divided into two hundred parts, and by estimation can be read to 1/100000 of an inch. Its constants are known, and it may be understood that it would not do to handle it very roughly. I could dwell here longer on this fascinating subject, but must haste. I may add that if this spherometer is placed on a plate of glass and exact contact obtained, and then removed, and the hand held over the plate without touching it, the difference in the temperature of the glass and that of the hand would be sufficient to distort the surface enough to be readily recognized by the spherometer when replaced. Any one desiring to investigate this subject further will find it fully discussed in that splendid series of papers by Dr. Alfred Mayer on the minute measurements of modern science published in SCIENTIFIC AMERICAN SUPPLEMENTS, to which I was indebted years ago for most valuable information, as well as to most encouraging words from Prof. Thurston, whom you all so well and favorably know. I now invite your attention to the method for testing the flat surfaces on which Prof. Rowland rules the beautiful diffraction gratings now so well known over the scientific world, as also other plane surfaces for heliostats, etc., etc. I am now approaching the border land of what may be called the abstruse in science, in which I humbly acknowledge it would take a vast volume to contain all I don't know; yet I hope to make plain to you this most beautiful and accurate method, and for fear I may forget to give due credit, I will say that I am indebted to Dr. Hastings for it, with whom it was an original discovery, though he told me he afterward found it had been in use by Steinheil, the celebrated optician of Munich. The principle was discovered by the immortal Newton, and it shows how much can be made of the ordinary phenomena seen in our every-day life when placed in the hands of the investigator. We have all seen the beautiful play of colors on the soap bubble, or when the drop of oil spreads over the surface of the water. Place a lens of long curvature on a piece of plane polished glass, and, looking at it obliquely, a black central spot is seen with rings of various width and color surrounding it. If the lens is a true curve, and the glass beneath it a true plane, these rings of color will be perfectly concentric and arranged in regular decreasing intervals. This apparatus is known as Newton's color glass, because he not only measured the phenomena, but established the laws of the appearances presented. I will now endeavor to explain the general principle by which this phenomenon is utilized in the testing of plane surfaces. Suppose that we place on the lower plate, lenses of constantly increasing curvature until that curvature becomes nil, or in other words a true plane. The rings of color will constantly increase in width as the curvature of the lens increases, until at last one color alone is seen over the whole surface, provided, however, the same angle of observation be maintained, and provided further that the film of air between the glasses is of absolutely the same relative thickness throughout. I say the film of air, for I presume that it would be utterly impossible to exclude particles of dust so that absolute contact could take place. Early physicists maintained that absolute molecular contact was impossible, and that the central separation of the glasses in Newton's experiment was 1/250,000 of an inch, but Sir Wm. Thomson has shown that the separation is caused by shreds or particles of dust. However, if this separation is equal throughout, we have the phenomena as described; but if the dust particles are thicker under one side than the other, our phenomena will change to broad parallel bands as in Fig. 8, the broader the bands the nearer the absolute parallelism of the plates. In Fig. 7 let a and b represent the two plates we are testing. Rays of white light, c, falling upon the upper surface of plate a, are partially reflected off in the direction of rays d, but as these rays do not concern us now, I have not sketched them. Part of the light passes on through the upper plate, where it is bent out of its course somewhat, and, falling upon the lower surface of the upper plate, some of this light is again reflected toward the eye at d. As some of the light passes through the upper plate, and, passing through the film of air between the plates, falling on the upper surface of the lower one, this in turn is reflected; but as the light that falls on this surface has had to traverse the film of air twice, it is retarded by a certain number of half or whole wave-lengths, and the beautiful phenomena of interference take place, some of the colors of white light being obliterated, while others come to the eye. When the position of the eye changes, the color is seen to change. I have not time to dwell further on this part of my subject, which is discussed in most advanced works on physics, and especially well described in Dr. Eugene Lommel's work on "The Nature of Light." I remarked that if the two surfaces were perfectly plane, there would be one color seen, or else colors of the first or second order would arrange themselves in broad parallel bands, but this would also take place in plates of slight curvature, for the requirement is, as I said, a film of air of equal thickness throughout. You can see at once that this condition could be obtained in a perfect convex surface fitting a perfect concave of the same radius. Fortunately we have a check to guard against this error. To produce a perfect plane, three surfaces must be worked together, unless we have a true plane to commence with; but to make this true plane by this method we must work three together, and if each one comes up to the demands of this most rigorous test, we may rest assured that we have attained a degree of accuracy almost beyond human conception. Let me illustrate. Suppose we have plates 1, 2, and 3, Fig. 11. Suppose 1 and 2 to be accurately convex and 3 accurately concave, of the same radius. Now it is evident that 3 will exactly fit 1 and 2, and that 1 and 2 will separately fit No. 3, but when 1 and 2 are placed together, they will only touch in the center, and there is no possible way to make three plates coincide when they are alternately tested upon one another than to make perfect planes out of them. As it is difficult to see the colors well on metal surfaces, a one-colored light is used, such as the sodium flame, which gives to the eye in our test, dark and bright bands instead of colored ones. When these plates are worked and tested upon one another until they all present the same appearance, one may be reserved for a test plate for future use. Here is a small test plate made by the celebrated Steinheil, and here two made by myself, and I may be pardoned in saying that I was much gratified to find the coincidence so nearly perfect that the limiting error is much less than 0.00001 of an inch. My assistant, with but a few months' experience, has made quite as accurate plates. It is necessary of course to have a glass plate to test the metal plates, as the upper plate must be transparent. So far we have been dealing with perfect surfaces. Let us now see what shall occur in surfaces that are not plane. Suppose we now have our perfect test plate, and it is laid on a plate that has a compound error, say depressed at center and edge and high between these points. If this error is regular, the central bands arrange themselves as in Fig. 9. You may now ask, how are we to know what sort of surface we have? A ready solution is at hand. The bands always travel in the direction of the thickest film of air, hence on lowering the eye, if the convex edge of the bands travel in the direction of the arrow, we are absolutely certain that that part of the surface being tested is convex, while if, as in the central part of the bands, the concave edges advance, we know that part is hollow or too low. Furthermore, any small error will be rigorously detected, with astonishing clearness, and one of the grandest qualities of this test is the absence of "personal equation;" for, given a perfect test plate, it won't lie, neither will it exaggerate. I say, won't lie, but I must guard this by saying that the plates must coincide absolutely in temperature, and the touch of the finger, the heat of the hand, or any disturbance whatever will vitiate the results of this lovely process; but more of that at a future time. If our surface is plane to within a short distance of the edge, and is there overcorrected, or convex, the test shows it, as in Fig. 10. If the whole surface is regularly convex, then concentric rings of a breadth determined by the approach to a perfect plane are seen. If concave, a similar phenomenon is exhibited, except in the case of the convex, the broader rings are near the center, while in the concave they are nearer the edge. In lowering the eye while observing the plates, the rings of the convex plate will advance outward, those of the concave inward. It may be asked by the mechanician, Can this method be used for testing our surface plates? I answer that I have found the scraped surface of iron bright enough to test by sodium light. My assistant in the machine work scraped three 8 inch plates that were tested by this method and found to be very excellent, though it must be evident that a single cut of the scraper would change the spot over which it passed so much as to entirely change the appearance there, but I found I could use the test to get the general outline of the surface under process of correction. These iron plates, I would say, are simply used for preliminary formation of polishers. I may have something to say on the question of surface plates in the future, as I have made some interesting studies on the subject. I must now bring this paper to a close, although I had intended including some interesting studies of curved surfaces. There is, however, matter enough in that subject of itself, especially when we connect it with the idiosyncrasies of the material we have to deal with, a vital part of the subject that I have not touched upon in the present paper. You may now inquire, How critical is this "color test"? To answer this I fear I shall trench upon forbidden grounds, but I call to my help the words of one of our best American physicists, and I quote from a letter in which he says by combined calculation and experiment I have found the limiting error for white light to be 1/50000000 of an inch, and for Na or sodium light about fifty times greater, or less than 1/800000 of an inch. Dr. Alfred Mayer estimated and demonstrated by actual experiment that the smallest black spot on a white ground visible to the naked eye is about 1/800 of an inch at the distance of normal vision, namely, 10 inches, and that a line, which of course has the element of extension, 1/5000 of an inch in thickness could be seen. In our delicate "color test" we may decrease the diameter of our black spot a thousand times and still its perception is possible by the aid of our monochromatic light, and we may diminish our line ten thousand times, yet find it just perceivable on the border land of our test by white light. Do not presume I am so foolish as to even think that the human hand, directed by the human brain, can ever work the material at his command to such a high standard of exactness. No; from the very nature of the material we have to work with, we are forbidden even to hope for such an achievement; and could it be possible that, through some stroke of good fortune, we could attain this high ideal, it would be but for a moment, as from the very nature of our environment it would be but an ignis fatuus. There is, however, to the earnest mind a delight in having a high model of excellence, for as our model is so will our work approximate; and although we may go on approximating our ideal forever, we can never hope to reach that which has been set for us by the great Master Workman.

[3]

A paper read before the Engineers' Society of Western Pennsylvania, Dec. 10, 1884.

[JOURNAL OF GAS LIGHTING.]

PHOTOMETRICAL STANDARDS.

In carrying out a series of photometrical experiments lately, I found that it was a matter of considerable difficulty to keep the flames of the standard candles always at their proper distance from the light to be measured, because the wick was continually changing its position (of course carrying the flame with it), and thus practically lengthening or shortening the scale of the photometer, according as the flame was carried nearer to or farther from the light at the other end of the scale. In order, therefore, to obtain a correct idea of the extent to which this variation of the position of the wick might influence the readings of the photometer scale, I took a continuous number of photographs of the flame of a candle while it was burning in a room quite free from draught; no other person being in it during the experiment except a photographer, who placed sensitive dry plates in a firmly fixed camera, and changed them after an exposure of 30 seconds. In doing this he was careful to keep close to the camera, and disturb the air of the room as little as possible. In front of the candle a plumb-line was suspended, and remained immovable over its center during the whole operation. The candle was allowed to get itself into a normal state of burning, and then the wick was aligned, as shown in the photographs Nos. 1 and 2, after which it was left to itself.

VARIATION IN PHOTOMETRICAL STANDARDS.

With these photographs (represented in the cuts) I beg to hand you full-sized drawings of the scales of a 100 inch Evans and a 60 inch Letheby photometer, in order to give your readers an opportunity of estimating for themselves the effect which such variations from the true distance between the standard light and that to be measured, as shown in this series of photographs, must exercise on photometrical observations made by the aid of either of the instruments named.

W. SUGG.

BLEACHING OR DYEING-YARNS AND GOODS IN VACUO.

Many attempts have been made to facilitate the penetration of textile fabrics by the dyeing and bleaching solutions, with which they require to be treated, by carrying out the treatment in vacuo, i.e., in such apparatus as shall allow of the air being withdrawn. The apparatus shown in the annexed engraving—Austrian Pat. Jan. 15, 1884—although not essentially different from those already in use, embodies, the Journal of the Society of Chemical Industry says, some important improvements in detail. It consists of a drum A, the sides of which are constructed of stout netting, carried on a vertical axis working through a stuffing-box, which is fitted in the bottom of the outer or containing vessel or keir B. The air can be exhausted from B by means of an air pump. A contains a central division P, also constructed of netting, into which is inserted the extremity of the tube R, after being twice bent at a right angle. P is also in direct connection with the efflux tube E, E and R serving to convey the dye or bleach solutions to and from the reservoir C. The combination of the rotary motion communicated to A, which contains the goods to be dyed or bleached, with the very thorough penetration and circulation of the liquids effected by means of the vacuum established in B, is found to be eminently favorable to the rapidity and evenness of the dye or bleach.

ON THE MOULDING OF PORCELAIN.

By CHAS. LAUTH.

The operation of moulding presents numerous advantages over other methods of shaping porcelain, for by this process we avoid irregularities of form, twisting, and visible seams, and can manufacture thin pieces, as well as pieces of large dimensions, of a purity of form that it is impossible to obtain otherwise.

The method of moulding small objects has been described with sufficient detail in technical works, but such is not the case with regard to large ones, and for this reason it will be of interest to quote some practical observations from a note that has been sent me by Mr. Constantine Renard, who, for several years, has had the superintendence of the moulding rooms of the Sevres works.

The process of moulding consists in pouring porcelain paste, thinned with water, into very dry plaster moulds. This mixture gradually hardens against the porous sides with which it is in contact, and, when the thickness of the hardened layer is judged sufficient, the mould is emptied by inverting it. The excess of the liquid paste is thus eliminated, while the thicker parts remain adherent to the plaster. Shortly afterward, the absorption of the water continuing, the paste so shrinks in drying as to allow the object to detach itself from the mould. As may be seen, nothing is simpler when it concerns pieces of small dimensions; but the same is not the case when we have to mould a large one. In this case we cannot get rid of the liquid paste by turning the mould upside down, because of the latter's size, and, on another hand, it is necessary to take special precautions against the subsidence of the paste. Recourse is therefore had to another method. In the first place, an aperture is formed in the lower part of the mould through which the liquid may flow at the desired moment. Afterward, in order to prevent the solidified but still slightly soft paste from settling under its own weight at this moment, it is supported by directing a current of compressed air into the mould, or, through atmospheric pressure, by forming a vacuum in the metallic jacket in which the mould is inclosed.

The history and description of these processes have been several times given, and I shall therefore not dwell upon them, but shall at once proceed to make known the new points that Mr. Renard has communicated to me.

The first point to which it is well to direct the manufacturer's attention is the preparation of the plaster moulds. When it concerns an object of large dimensions, of a vase a yard in height, for example, the moulder is obliged to cut the form or core horizontally into three parts, each of which is moulded separately. To this effect, it is placed upon a core frame and surrounded with a cylinder of sheet zinc. The workman pours the plaster into the space between the latter and the core, and, while doing so, must stir the mass very rapidly with a stick, so that at the moment the plaster sets, it shall be as homogeneous as possible. In spite of such precautions, it is impossible to prevent the densest parts of the plaster from depositing first, through the action of gravity. These will naturally precipitate upon the table or upon the slanting sides of the core, and the mould will therefore present great inequalities as regards porosity. Since this defect exists in each of the pieces that have been prepared in succession, it will be seen that when they come to be superposed for the moulding of the piece, the mould as a whole will be formed of zones of different porosities, which will absorb water from the paste unequally. Farther along we shall see the inconveniences that result from this, and the manner of avoiding them.

FIG. 1

The mould, when finished, is dried in a stove. Under such circumstances it often happens that there forms upon the surface of the plaster a hard crust which, although it is of no importance as regards the outside of the mould, is prejudicial to the interior because it considerably diminishes its absorbing power. This trouble may be avoided by coating the surfaces that it is necessary to preserve with clear liquid paste; but Mr. Renard advises that the mould be closed hermetically, so that the interior shall be kept from contact with warm air. In this way it is possible to prevent the plaster from hardening, as a result of too quick a desiccation. I now come to the operation of moulding. In the very first place, it is necessary to examine whether it is well to adopt the arrangement by pressure of air or by vacuum. The form of the objects will determine the choice. A very open piece, like a bowl, must be moulded by vacuum, on account of the difficulty of holding the closing disk in place if it be of very large dimensions. The same is the case with large vases of wood form. On the contrary, an elongated piece tapering from above is more easily moulded by pressure of the air, as are also ovoid vessels 16 to 20 inches in height. In any case it must not be forgotten that the operation by vacuum should be preferred every time the form of the objects is adapted to it, because this process permits of following and directing the drying, while with pressure it is impossible to see anything when once the apparatus is closed.

FIG. 2.

Moulding by Pressure of the Air.—The plaster mould having been put in place upon the mould board, and the liquid paste having been long and thoroughly stirred in order to make it homogeneous, and get rid of the air bubbles, we open the cock that puts the paste reservoir in communication with the lower part of the mould, care having been taken beforehand to pour a few pints of water into the bottom of the mould. The paste in ascending pushes this water ahead of it, and this slightly wets the plaster and makes the paste rise regularly. When the mould is entirely filled, the paste is still allowed to flow until it slightly exceeds the upper level, and, spreading out over the entire thickness of the plaster, forms a sort of thick flange. The absorption of the liquid begins almost immediately, and, consequently, the level lowers. A new quantity of paste is introduced, and we continue thus, in regulating its flow so as to keep the mould always full. This operation is prolonged until the layer is judged to be sufficiently thick, this depending upon the dimensions, form, or construction of the vessel. The operation may take from one to five hours.

The desired thickness having been obtained, it becomes a question of allowing the paste to descend and at the same time to support the piece by air pressure. The flange spoken of above is quickly cut, and the paste is made to rise again for the last time, in order to form a new flange, but one that this time will be extremely thin; then a perforated disk designed for forming the top joint, and acting as a conduit for the air, is placed upon the mould. This disk is fastened down with a screw press, and when the apparatus is thus arranged the eduction cock is opened, and the air pump maneuvered.

If the flange did not exist, the air would enter between the mould and the piece at the first strokes of the piston, and the piece would be inevitably broken. Its object, then, is to form a hermetical joint, although it must at the same time present but a slight resistance, since, as soon as the liquid paste has flowed out, the piece begins to shrink, and it is necessary that at the first movement downward it shall be able to disengage itself, since it would otherwise crack.

As soon as the piece begins to detach itself from the mould the air enters the apparatus, and the pressure gauge connected with the air pump begins to lower. It is then necessary, without a moment's loss of time, to remove the screw press, the disk, and the upper part of the mould itself, in order to facilitate as much as possible the contraction of the piece. Finally, an hour or an hour and a half later, it is necessary to remove the lower part of the mould, this being done in supporting the entire affair by the middle. The piece and what remains of the mould are, in reality, suspended in the air. All these preparations are designed to prevent cracking.

Moulding by Vacuum.—The operation by vacuum follows the same phases as those just described. It is well, in order to have a very even surface, not to form a vacuum until about three hours after the paste has been made to ascend. Without such a precaution the imperfections in the mould will be shown on the surface of the object by undulations that are irremediable.

The first flange or vein must be preserved, and it is cut off at the moment the piece is detached.

Moulding by vacuum, aside from the advantages noted above, permits of giving the pieces a greater thickness than is obtained in the pressure process. According to Mr. Renard, when it is desired to exceed one inch at the base of the piece (the maximum thickness usually obtained), the operation is as follows: The piece is moulded normally, and it is supported by a vacuum; but, at the moment at which, under ordinary circumstances, it would be detached, the paste is made to ascend a second time, when the first layer (already thick and dry) acts as a sort of supplementary mould, and permits of increasing the thickness by about ⅖ of an inch. The piece is held, as at first, by vacuum, and the paste is introduced again until the desired thickness is obtained.

Whatever be the care taken, accidents are frequent in both processes. They are due, in general, to the irregular contraction of the pieces, caused by a want of homogeneousness in the plaster of the moulds. In fact, as the absorption of the water does not proceed regularly over the entire surface of the piece, zones of dry paste are found in contact with others that are still soft, and hence the formation of folds, and finally the cracking and breaking of the piece. The joints of the moulds are also a cause of frequent loss, on account of the marks that they leave, and that injure the beauty of the form as well as the purity of the profile.

Mr. Renard has devised a remedy for all such inconveniences. He takes unglazed muslin, cuts it into strips, and, before beginning operations, fixes it with a little liquid paste to the interior of the mould. This light fabric in no wise prevents the absorption of the water, and so the operation goes on as usual; but, at the moment of contraction, the piece of porcelain being, so to speak, supported by the muslin, comes put of the mould more easily and with extreme regularity. Under such circumstances all trace of the joint disappears, the imperfections in the mould are unattended with danger, and the largest pieces are moulded with entire safety. In a word, we have here a very important improvement in the process of moulding. The use of muslin is to be recommended, not only in the manufacture of vases, but also in the difficult preparation of large porcelain plates. It is likewise advantageous in the moulding of certain pieces of sculpture that are not very delicate, and, finally, it is very useful when we have to do with a damaged mould, which, instead of being repaired with plaster, can be fixed with well ground wet sand covered with a strip of muslin.

Drying of the Moulded Pieces.—When the moulded pieces become of a proper consistency in the mould, they are exposed to the air and then taken to the drying room. But, as with plaster, the surface of the paste dries very quickly, and this inconvenience (which amounts to nothing in pieces that are to be polished) is very great in pieces that carry ornaments in relief, since the finishing of these is much more difficult, the hardened paste works badly, and frequently flakes off. In order to remedy this inconvenience, it suffices to dust the places to be preserved with powdered dry paste.—Revue Industrielle.

PHOTO-TRICYCLE APPARATUS.

A PHOTO-TRICYCLE APPARATUS.

This consists of a portable folding camera, with screw focusing arrangement, swing back, and an adapter frame placed in the position of the focus screen, allowing the dark slide to be inserted so as to give the horizontal or vertical position to the dry plate when in the camera. To the front and base-board a brass swiveled side bar, made collapsible by means of a center slot, is attached by hinges, and this renders the camera rigid when open or secure when closed. The base-board is supported on a brass plate within which is inserted a ball-and-socket (or universal joint in a new form), permitting the camera to be tilted to any necessary angle, and fixed in such position at will. The whole apparatus is mounted upon a brass telescopic draw-stand, which, by means of clamps, is attached to the steering handle or other convenient part of the tricycle, preferably the form made by Messrs. Rudge & Co., of Coventry, represented in the cut.—Photo. News.

A PHOTO PRINTING LIGHT.

A printing frame is placed in the carrier, and exposed to the light of a gas burner kept at a fixed distance, behind which is a spherical reflector. The same frame may be used for other purposes.-Photographic News.

A NEW ACTINOMETER.

A selenium actinometer has been described in the Comptes Rendus in a communication from M. Morize, of Rio de Janeiro. The instrument is used to measure the actinic power of sunlight when the sun is at various altitudes; but the same principle is applicable to other light sources. The sensitive part of the apparatus consists of a cylinder formed of 38 disks of copper, isolated from each other by as many disks of mica. The latter being of smaller diameter than the copper disks, the annular spaces between the two are filled with selenium, by the simple process of rubbing a stick of this substance over the edges, and afterward gently warming. The selenium then presents a grayish appearance, and is ready for use. Connection is made by conductors, on opposite sides, with the odd and even numbers of the disks, which diminishes the resistance of the selenium. The cylinder thus formed is insulated by glass supports in the inside of a vacuum tube, for the purpose of preserving it from the disturbing influence of dark rays. The whole is placed upon a stand, and shielded from reflected light, but fully exposed to that which is to be measured for actinic intensity. If now a constant current of electricity is passed through the apparatus, as indicated by a galvanometer, the variations of the latter will show the effect produced upon the selenium. A scale must be prepared, with the zero point at the greatest possible resistance of the selenium, which corresponds with absolute darkness. The greatest effect of the light would be to annul the resistance of the selenium. Consequently, the cylinder must be withdrawn from the circuit to represent this effect; and the maximum deviation of the galvanometer is then to be observed, and marked 100. By dividing the range of the galvanometer thus obtained into 100 equal parts, the requisite actinometric scale will be established. In practice, the Clamond battery is used to supply the constant current required.

ASTRONOMICAL PHOTOGRAPHY.

During the last few years, or rather decades of years, it has become rather a trite saying that to advance far in any branch of physical research a fair proficiency in no inconsiderable number of the sister sciences is an absolute necessity. But if this is true in general, none, I think, will question the assertion that a proficient in any of the physical sciences must be fairly conversant with photography as a science, or at least as an art. If we take for example a science which has of late years made rapid strides both in Europe and America, the science of astronomy, we shall not have far to go to find convincing proof that a great portion of the best work that is being done by its votaries is effected by the aid of photography. One eminent astronomer has quite lately gone so far as to declare that we no longer require observers of the heavens, but that their place can be better supplied by the gelatine plate of the photographer; and his words have been echoed by others not less able than himself. "Abolish the observer, and substitute the sensitive plate," is a sensational form of expressing the revolution in observational astronomy that is taking place under our eyes; but, although it suggests a vast amount of truth, it might leave upon the mind an exaggerated impression inimical to the best interests of science.

The award of the highest distinction in astronomy, the gold medal of the Royal Astronomical Society, two years in succession, to those who have been most successful in celestial photography is no doubtful sign of the great value attached to such work. Last year it was Mr. Common who received the highest testimony of the merit due to his splendid photographs of the nebula of Orion; and this year Dr. Huggins, who has drawn much attention to celestial photography, by his successful attempts to picture the solar corona in full daylight, has received a similar acknowledgment of his labors in photographing the spectra of stars and comets and nebulæ.

An adequate idea of the progress astronomy is now making by aid of photography can only be formed by a comprehensive view of all that is being at present attempted; but a rapid glance at some of the work may prepare the way for a more thorough investigation. A few years since, the astronomers who had advanced their science by aid of photography were few in number, and their results are soon enumerated. Some good pictures of the solar corona taken during solar eclipses, a series or two of sun-spot photographs, and a very limited number of successful attempts made upon the moon, and planets, and star clusters, were all the fruits of their labors. But now each month we learn of some new and efficient laborer in this field, which gives promise of so rich a harvest.

Each day the sun is photographed at Greenwich, at South Kensington, in India, and at the Physical Observatory of Potsdam, and thus a sure record is obtained of all the spots upon its surface, which may serve for the study of the periodicity of its changes, and for their probable connection with the important phenomena of terrestrial magnetism and meteorology. In France the splendid sun-pictures obtained by Dr. Janssen at the Physical Observatory of Meudon have thrown into the shade all other attempts at a photographic study of the most delicate features of the solar surface.

Dr. Huggins has shown that it is possible to obtain a daily photographic record of the solar prominences, and only lately he has secured results that justified a special expedition to the Alps to photograph the sun's corona, and he has now moved the Admiralty to grant a subsidy to Dr. Gill, the government astronomer at the Cape, by aid of which Mr. Woods can carry on the experiments that were so encouraging last summer in Switzerland.

We may, then, reasonably hope to obtain before long a daily picture of the sun and a photographic record of its prominences, and even of a certain portion of the solar corona; but the precious moments of each solar eclipse will always be invaluable for picturing those wondrous details in the corona that are now shown us by photography, and which can be obtained by photography alone.

Again, how very much is to be learnt in solar physics from the marvelous photographs of the sun's spectrum exhibited last summer by Professor Rowland; photographs that show as many as one hundred and fifty lines between H and K, and which he is still laboring to improve! The extension, too, of the visible solar spectrum into the ultra-violet by Corun, Mascart, and others, adds much to our knowledge of the sun; while the photographs of Abney in the ultrared increase our information in a direction less expected and certainly less easy of attainment. Both these extensions we find most ably utilized in the recent discussion of the very interesting photographs of the spectra of the prominences and of the corona taken during the total eclipse of May 18, 1882; and the photographic results of this eclipse afford ample proof that we can not only obtain pictures of the corona by photography that it would be impossible otherwise to procure, but also that in a few seconds information concerning the nature of the solar atmosphere may be furnished by photography that it would otherwise take centuries to accumulate, even under the most favorable circumstances.

The advantages to be gained by accurate photographs of the moon and planets, that will permit great enlargements, are too obvious to call for lengthened notice in such a rapid sketch as the present; for it is principally in the observation of details that the eye cannot grasp with the required delicacy, or with sufficient rapidity, that photography is so essential for rapid and sure progress.

Like the sketches of a solar eclipse, the drawings that are made of comets, and still more of nebulæ, even by the most accomplished artists, are all, to say the least, open to doubt in their delicate details. And the truth of this is so obvious, that it is the expressed opinion of an able astronomer that a single photograph of the nebula of Orion, taken by Mr. Common, would be of more value to posterity than the collective drawings of this interesting object so carefully made by Rosse, Bond, Secchi, and so many others.

Another most important branch of astronomy, that is receiving very great attention at present, is the mapping of the starry heavens; and herein photography will perhaps do its best work for the astronomer. The trial star map by the brothers Henry, of a portion of the Milky Way, which they felt unable to observe satisfactorily by the ordinary methods, is so near absolute perfection that it alone proves the immense superiority of the photographic method in the formation of star maps. Fortunately this subject, which is as vast as it is fundamental, is being taken up vigorously. The Henries are producing a special lens for the work; Mr. Grubb is constructing a special Cassgrain reflector for Mr. Roberts of Maghull; and the Admiralty have instructed Mr. Woods to make this part of his work at the Cape Observatory, under the able direction of Dr. Gill. Besides star maps, clusters, too, and special portions of the heavens are being photographed by the Rev. T.E. Espin, of West Kirby; and such pictures will be of the greatest value, not only in fixing the position at a given date, but also aiding in the determination of magnitude, color, variability, proper motion, and even of the orbits of double and multiple stars, and the possible discovery of new planets and telescopic comets.

Such are some of the many branches of astronomy that are receiving the most valuable aid at present from photography; but the very value of the gift that is bestowed should make exaggeration an impossibility. Photography can well afford to be generous, but it must first be just, in its estimate of the work that has still to be done in astronomy independently of its aid; and although the older science points with just pride to what is being done for her by her younger sister, still she must not forget that now, as in the future, she must depend largely for her progress, not only on the skill of the photographer and the mathematician, but also on the trained eye and ear and hand of her own indefatigable observers.—S.J. Perry, S.J., F.R.S., in Br. Jour. of Photography.

ELECTRICITY AS A PREVENTIVE OF SCALE IN BOILERS.

The mineral sediment that generally sticks to the sides of steam boilers, and the presence of which is fraught with the utmost danger, resulting in many instances in great injury to life and property, besides eating away the substance of the iron plate, was referred to in a paper lately read by M. Jeannolle before the Paris Academy of Sciences, in which the author described a new method for keeping boilers clean. This method is as follows:

The inside of a steam boiler is placed, by means of piles of a certain power, in reciprocal communication, the current passing at one end through positive, and at the other through negative, wires. In incrusted steam boilers, at a temperature ranging from 212° to 300° Fahr., and a pressure of from 30 to 90 lb. to the square inch, the current thus engendered decomposes the accumulated salts, and precipitates them, from which they may easily be removed, either by means of a special siphon or by means of some other mechanical process. When boilers are free from fur, and where it is intended to keep them free from such, a continuous current may be set up, by means of which the sedimentary salts may be decomposed, and a precipitate produced in a pulverized form, which can be removed with equal facility.

From a series of minute experiments made by M. Jeannolle, it appears that in order to render the various actions of electricity, perfect, it is necessary to coat either with red lead or with pulverized iron, or with any other conductor of electricity, an operation which must be repeated whenever the boiler is emptied with a view to cleaning out. The above system Is being advantageously applied in Calais for removing the incrustations of boilers. The two poles of a battery of ten to twelve Bunsen elements are applied to the ends of the boilers, and after thirty to forty hours the deposits fall from the sides to the bottom. When a boiler has been thus cleared, the formation of new deposits may be prevented by applying a much less energetic current under the same conditions.

ALPHABET DESIGNED BY GODFREY SYKES.

SUGGESTIONS IN DECORATIVE ART.—ALPHABET DESIGNED BY GODFREY SYKES.

Among the many designs which have been issued by the South Kensington Museum authorities is the alphabet which we have illustrated here to-day. The letters appear frequently among the decorations of the museum buildings, especially in the refreshment rooms and the Ceramic gallery, where long inscriptions in glazed terra cotta form ornamental friezes. The alphabet has also been engraved to several sizes, and is used for the initial letters in the various official books and art publications relating to the museum, which are published by the Science and Art Department.—Building News.

OLD WROUGHT IRON GATE.

OLD WROUGHT IRON GATE

This gate forms the entrance to Scraptoft Hall, a building of the eighteenth century, now the seat of Captain Barclay, and which stands at about five miles from Leicester, England.—The Architect.

BRIEF SANITARY MATTERS IN CONNECTION WITH ISOLATED COUNTRY HOUSES.[^[4]]

By E.W. BOWDITCH, C.E.