SCIENTIFIC AMERICAN SUPPLEMENT NO. 717
NEW YORK, SEPTEMBER 28, 1889.
Scientific American Supplement. Vol. XXVIII., No. 717.
Scientific American established 1845.
Scientific American Supplement, $5 a year.
Scientific American and Supplement, $7 a year.
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TABLE OF CONTENTS.
I. CIVIL ENGINEERING.—The Girard Hydraulic Railway.—One of the great curiosities of the Paris exposition, the almost frictionless railway, with sectional illustrations of its structure.—8 illustrations. 11451
II. ELECTRICITY.—Early Electric Lighting.—Electric lighting in Salem in 1859, a very curious piece of early history. 11458
Electric Motor for Alternating Currents.—A motor on an entirely new principle for the application of the alternating current with results obtained, and the economic outlook of the invention. 11458
Portable Electric Light.—A lamp for military and other use, in which the prime motor, including the boiler and the lamp itself, are carried on one carriage.—1 illustration. 11458
The Electric Age.—By CHARLES CARLETON COFFIN.—A short resume of the initial achievements of modern electricity. 11458
III. GEOLOGY.—The Fuels of the Future.—A prognosis of the future prospect of the world as regards a fuel supply, with a special reference to the use of natural gas. 11457
IV. MISCELLANEOUS.—Preservation of Spiders for the Cabinet.—A method of setting up spiders for preservation in the cabinet, with formulae of solutions used and full details of the manipulation.—1 illustration. 11461
The Ship in the New French Ballet of the "Tempest."—A curious example of modern scenic perfection, giving the construction and use of an appliance of the modern ballet.—5 illustrations. 11450
V. NAVAL ENGINEERING.—Crank and Screw Shafts of the Mercantile Marine.—By G. W. MANUEL.—This all-important subject of modern naval engineering treated in detail, illustrating the progress of the present day, the superiority of material and method of using it, with interesting practical examples.—1 illustration. 11448
Experimental Aid in the Design of High Speed Steamships.—By D. P.—A plea for the experimental determination of the probable speed of ships, with examples of its application in practice. 11449
Forging a Propeller Shaft.—How large steamer shafts are forged, with example of the operation as exhibited to the Shah of Persia at Brown & Co.'s works, Sheffield, England.—1 illustration. 11447
The Naval Forges and Steel Works at St. Chamond.—The forging of a piece of ordnance from a 90 ton ingot of steel, an artistic presentation of the subject.—1 illustration. 11447
VI. PHOTOGRAPHY.—The Pyro Developer with Metabisulphite of Potash.—By Dr. J. M. EDER.—A new addition to the pyro developer, with formulae and results. 11462
VII. PHYSICS.—Quartz Fibers.—A lecture by Mr. C. V. BOYS on his famous experiments of the production of microscopic fibers, with enlarged illustrations of the same, and a graphic account of the entire subject.—7 illustrations. 11452
The Modern Theory of Light.—By Prof. OLIVER LODGE.—An abstract of a lecture by the eminent investigator and expositor of Prof. Hertz's experiments, giving a brief review of the present aspect of this absorbing question. 11459
VIII. PHYSIOLOGY.—Heat in Man.—Experiments recently made by Dr. Loewy on the heat of the human system.—Described and commented on by Prof. ZUNTZ. 11461
IX. SANITATION.—On Purification of Air by Ozone—with an Account of a New Method.—By Dr. B. W. RICHARDSON.—A very important subject treated in full, giving the past attempts in the utilization of ozone and a method now available. 11460
X. TECHNOLOGY.—Alkali Manufactories.—Present aspect of the Leblanc process and the new process for the recovery of sulphur from its waste. 11457
Dried Wine Grapes.—The preparation of the above wine on a large scale in California, with full details of the process adopted. 11461
The Production of Ammonia from Coal.—By LUDWIG MOND.—A valuable review of this important industry, with actual working results obtained in carrying out a retort process.—2 illustrations. 11454
Nature, Composition, and Treatment of Animal and Vegetable Fabrics.—The history of fabrics and fibers in the vegetable and animal world, their sources, applications, and treatments. 11453
Walnut Oil.—By Thomas T. P. BRUCE WARREN.—An excellent oil for painters' use, with description of a simple method for preparing it on a small scale. 11462
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THE NAVAL FORGES AND STEEL WORKS AT ST. CHAMOND.
With the idyls and historic or picturesque subjects that the Universal Exposition gives us the occasion to publish, we thought we would make a happy contrast by selecting a subject of a different kind, by presenting to our readers Mr. Layraud's fine picture, which represents the gigantic power hammer used at the St. Chamond Forges and Steel Works in the construction of our naval guns. By the side of the machinery gallery and the Eiffel tower this gigantic apparatus is well in its place.
The following is the technical description that has been given to us to accompany our engraving: In an immense hall, measuring 260 ft. in length by 98 ft. in width, a gang of workmen has just taken from the furnace a 90 ton ingot for a large gun for an armor-clad vessel. The piece is carried by a steam crane of 140 tons power, and the men grouped at the maneuvering levers are directing this incandescent mass under the power hammer which is to shape it. This hammer, whose huge dimensions allow it to take in the object treated, is one of the largest in existence. Its striking mass is capable of reaching 100 tons, and the height of the fall is 16 ft. To the left of the hammer is seen a workman getting ready to set it in motion. It takes but one man to maneuver this apparatus, and this is one of the characteristic features of its construction.
The beginning of this hammer's operation, as well as the operations of the forge itself, which contains three other hammers of less power, dates back to 1879. It is with this great hammer that the largest cannons of the naval artillery—those of 16 inches—have been made (almost all of which have been manufactured at St. Chamond), and those, too, of 14, 13, and 12 inches. This is the hammer, too, that, a few months ago, was the first to be set at work on the huge 13 in. guns of new model, whose length is no less than 52 ft. in the rough.
Let us add a few more figures to this account in order to emphasize the importance of the installations which Mr. Layraud's picture recalls, and which our great French industry has not hesitated to establish, notwithstanding the great outlay that they necessitated. This huge hammer required foundations extending to a depth of 32 ft., and the amount of metal used in its construction was 2,640,000 pounds. The cost of establishing the works with all the apparatus contained therein was $400,000.—Le Monde Illustre.
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FORGING A PROPELLER SHAFT.
During the recent visit of the Shah of Persia to England, he visited, among other places, the great works of John Brown & Co., at Sheffield, and witnessed the pressing of a propeller shaft for one of the large ocean steamships. The operation is admirably illustrated in our engraving, for which we are indebted to the Illustrated London News.
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CRANK AND SCREW SHAFTS OF THE MERCANTILE MARINE.
By G. W. MANUEL.
[Footnote 1: A paper read before the Institute of Marine Engineers, Stratford, 1889.]
Being asked to read a paper before your institute, I have chosen this subject, as I think no part of the marine engine has given so much trouble and anxiety to the seagoing engineer; and from the list of shipping casualties in the daily papers, a large proportion seem due to the shafting, causing loss to the shipowner, and in some instances danger to the crew. My endeavor is to put some of the causes of these casualties before you, also some of the remedies that have tended to reduce their number. Several papers have been read on this subject, chiefly of a theoretical description, dealing with the calculations relating to the twisting and bending moments, effects of the angles of the cranks, and length of stroke—notably that read by Mr. Milton before the Institute of Naval Architects in 1881. The only practical part of this paper dealt with the possibility of the shafts getting out of line; and regarding this contingency Dr. Kirk said that "if superintendent engineers would only see that the bearings were kept in line, broken crank and other shafts would not be so much heard of." Of course this is one of those statements made in discussions of this kind, for what purpose I fail to see, and as far as my own experience goes is misleading; for having taken charge of steamers new from the builders' hands, when it is at least expected that these shafts would be in line, the crank shaft bearings heated very considerably, and continued to do so, rendering the duration of life of the crank shaft a short one; and though they were never what is termed out of line, the bearings could not be kept cool without the use of sea water, and occasionally the engines had to be stopped to cool and smooth up the bearing surfaces, causing delays, worry, and anxiety, for which the engineer in charge was in no way responsible. Happily this state of what I might call uncertainties is being gradually remedied, thanks being largely due to those engineers who have the skill to suggest improvements and the patience to carry them out against much opposition.
These improvements in many instances pertain to the engine builder's duties, and are questions which I think have been treated lightly; notably that of insufficient bearing surface, and one of the principal causes of hot bearings, whereby the oil intended for lubrication was squeezed out, and the metal surfaces brought too close in contact; and when bearings had a pressure of 200 lb. per square inch, it has been found that not more than 120 lb. per square inch should be exerted to keep them cool (this varies according to the material of which the bearing is composed), without having to use sea water and prevent them being ground down, and thus getting out of line. I have known a bearing in a new steamer, in spite of many gallons of oil wasted on it, wear down one-eighth of an inch in a voyage of only 6,000 miles, from insufficiency of bearing surface.
Several good rules are in use governing the strength of shafts, which treat of the diameter of the bearings only and angles of the cranks; and the engine builder, along with the ship owner, has been chary of increasing the surfaces by lengthening the bearings; for to do this means increase of space taken up fore and aft the vessel, besides additional weight of engine. Engine builders all aim in competing to put their engines in less space than their rivals, giving same power and sometimes more. I think, however, this inducement is now more carefully considered, as it has been found more economical to give larger bearing surfaces than to have steamers lying in port, refitting a crank shaft, along with the consequences of heavy bills for salvage and repairs, also the risk of losing the steamer altogether. Proportioning the bearings to the weights and strains they have to carry has also been an improvement. The different bearings of marine engines were usually made alike in surface, irrespective of the work each had to do, with a view to economy in construction.
In modern practice the after bearings have more surface than the forward, except in cases where heavy slide-valve gear has to be supported, so that the wear down in the whole length of the shaft is equal, thus avoiding those alternate bending strains at the top and bottom of the stroke every revolution. Another improvement that has been successfully introduced, adding to the duration of life of crank shafts, is the use of white bearing metal, such as Parson's white brass, on which the shafts run smoothly with less friction and tendency to heat, so that, along with well proportioned surfaces, a number of crank shafts in the Peninsular and Oriental Co.'s service have not required lining up for eight years, and I hope with care may last till new boilers are required. Large and powerful steamers can be driven full speed from London to Australia and back without having any water on the bearings, using oil of only what is considered a moderate price, allowing the engineer in charge to attend to the economical working of both engines and boilers (as well as many other engines of all kinds now placed on board a large mail and passenger steamer), instead of getting many a drenching with sea water, and worried by close attention to one or two hot bearings all the watch. Compare these results with the following: In the same service in 1864, and with no blame to the engineer in charge, the crank shaft bearings of a screw steamer had to be lined up every five days at intermediate ports, through insufficient bearing surfaces. Sea water had continually to be used, resulting in frequent renewal of crank shaft. Steamers can now run 25,000 miles without having to lift a bearing, except for examination at the end of the voyage. I would note here that the form of the bearings on which the shafts work has also been much improved. They are made more of a solid character, the metal being more equally disposed round the shaft, and the use of gun metal for the main bearings is now fast disappearing. In large engines the only metals used are cast iron and white brass, an advantage also in reducing the amount of wear on the recess by corrosion and grinding where sea water was used often to a considerable extent.
Figs. No. 1 and No. 2 show the design of the old and new main bearings, and, I think, require but little explanation. Most of you present will remember your feelings when, after a hot bearing, the brasses were found to be cracked at top and bottom, and the trouble you had afterward to keep these brasses in position. When a smoking hot bearing occurred, say in the heating of a crank pin, it had the effect of damaging the material of the shaft more or less, according to its original soundness, generally at the fillets in the angles of the cranks. For when the outer surface of the iron got hot, cold water, often of a low temperature, was suddenly poured on, and the hot iron, previously expanded, was suddenly contracted, setting up strains which in my opinion made a small tear transversely where the metal was solid; and where what is termed lamination flaws, due to construction, existed, these were extended in their natural direction, and by a repetition of this treatment these flaws became of such a serious character that the shafts had to be condemned, or actually gave way at sea. The introduction of the triple expansion engine, with the three cranks, gave better balance to the shaft, and the forces acting in the path of the crank pin, being better divided, caused more regular motion on the shaft, and so to the propeller. This is specially noticeable in screw steamers, and is taken advantage of by placing the cabins further aft, nearer the propeller, the stern having but little vibration; the dull and heavy surging sound, due to unequal motions of the shaft in the two-crank engines, is exchanged for a more regular sound of less extent, and the power formerly wasted in vibrating the stern is utilized in propelling the vessel. In spite of all these improvements I have mentioned, there remains the serious question of defects in the material, due to variety of quality and the extreme care that has to be exercised in all the stages during construction of crank or other shafts built of iron. Many shafts have given out at sea and been condemned, through no other cause than original defects in their construction and material.
The process of welding and forging a crank shaft of large diameter now is to make it up of so many small pieces, the best shafts being made of what is termed scrap, representing thousands of small pieces of selected iron, such as cuttings of old iron boiler plates, cuttings off forgings, old bolts, horseshoes, angle iron, etc., all welded together, forged into billets, reheated, and rolled into bars. It is then cut into lengths, piled, and formed into slabs of suitable size for welding up into the shafts. No doubt this method is preferable to the old method of "fagoting," so called, as the iron bars were placed side by side, resembling a bundle of fagots of about 18 or 20 inches square.
The result was that while the outside bars would be welded, the inside would be improperly welded, or, the hammer being weak, the blow would be insufficient to secure the proper weld, and it was no uncommon thing for a shaft to break and expose the internal bars, showing them to be quite separate, or only partially united. This danger has been much lessened in late years by careful selection of the materials, improved methods of cleaning the scrap, better furnaces, the use of the most suitable fuels, and more powerful steam hammers. Still, with all this care, I think I may say there is not a shaft without flaws or defects, more or less, and when these flaws are situated in line of the greatest strains, and though you may not have a hot bearing, they often extend until the shaft becomes unseaworthy.
[Diagrams shown illustrated the various forms of flaws.] These flaws were not observable when the shafts were new, although carefully inspected. They gradually increased under strain, came to the outside, and were detected. Considerable loss fell upon the owners of these vessels, who were in no way to blame; nor could they recover any money from the makers of the shafts, who were alone to blame. I am pleased to state, and some of the members here present know, that considerable improvement has been effected in the use of better material than iron for crank shafts, by the introduction of a special mild steel, by Messrs. Vickers, Sons & Co., of Sheffield, and that instead of having to record the old familiar defects found in iron shafts, I can safely say no flaws have been observed, when new or during eight years running, and there are now twenty-two shafts of this mild steel in the company's service.
I may here state that steel was used for crank shafts in this service in 1863, as then manufactured in Prussia by Messrs. Krupp, and generally known as Krupp's steel, the tensile strength of which was about 40 tons per square inch, and though free from flaws, it was unable to stand the fatigue, and broke, giving little warning. It was of too brittle a nature, more resembling chisel steel. It was broken again under a falling weight of 10 cwt. with a 10 ft. drop = 121/2 tons.
The mild steel now used was first tried in 1880. It possessed tensile strength of 24 to 25 tons per square inch. It was then considered advisable not to exceed this, and err rather on the safe side. This shaft has been in use eight years, and no sign of any flaw has been observed. Since then the tensile strength of mild steel has gradually been increased by Messrs. Vickers, the steel still retaining the elasticity and toughness to endure fatigue. This has only been arrived at by improvements in the manufacture and more powerful and better adapted hammers to forge it down from the large ingots to the size required. The amount of work they are now able to subject the steel to renders it more fit to sustain the fatigue such as that to be endured by a crank shaft. These ingots of steel can be cast up to 100 tons weight, and require powerful machines to deal with them. For shafts say of 20 inches diameter, the diameter of the ingot would be about 52 inches. This allows sufficient work to be put on the couplings, as well as the shaft. To make solid crank shafts of this material, say of 19 inches diameter, the ingot would weigh 42 tons, the forging, when completed, 17 tons, and the finished shaft 113/4 tons; so that you see there is 25 tons wasted before any machining is done, and 51/4 tons between the forging and finished shaft. This makes it very expensive for solid shafts of large size, and it is found better to make what is termed a built shaft; the cranks are a little heavier, and engine framings necessarily a little wider, a matter comparatively of little moment. I give you a rough drawing of the hydraulic hammer, or strictly speaking a press, used by Messrs. Vickers in forging down the ingots in shafts, guns, or other large work. This hammer can give a squeeze of 3,000 tons. The steel seems to yield under it like tough putty, and, unlike the steam hammer, there is no jarring on the material, and it is manipulated with the same ease as a small hammer by hydraulics.
The tensile strength of steel used for shafts having increased from 24 to 30 tons, and in some cases 31 tons, considering that this was 2 tons above that specified, and that we were approaching what may be termed hard steel, I proposed to the makers to test this material beyond the usual tests, viz., tensile, extension, and cold bending test. The latter, I considered, was much too easy for this fine material, as a piece of fair iron will bend cold to a radius of 11/2 times its diameter or thickness, without fracture; and I proposed a test more resembling the fatigue that a crank shaft has sometimes to stand, and more worthy of this material; and in the event of its standing this successfully, I would pass the material of 30 or 31 tons tensile strength. Specimens of steel used in the shafts were cut off different parts—crank pins and main bearings—(the shafts being built shafts) and roughly planed to 11/2 inches square, and about 12 inches long. They were laid on the block as shown, and a cast iron block, fitted with a hammer head 1/2 ton weight, let suddenly fall 12 inches, the block striking the bar with a blow of about 4 tons. The steel bar was then turned upside down, and the blow repeated, reversing the piece every time until fracture was observed, and the bar ultimately broken. The results were that this steel stood 58 blows before showing signs of fracture, and was only broken after 77 blows. It is noticeable how many blows it stood after fracture. A bar of good wrought iron, undressed, of same dimensions, was tried, and broke the first blow. A bar cut from a piece of iron to form a large chain, afterward forged down and only filed to same dimensions, broke at 25 blows. I was well satisfied with the results, and considered this material, though possessing a high tensile strength, was in every way suitable for the construction and endurance required in crank shafts.
Sheet No. 1 shows you some particulars of these tests:
Tensile Elong. Fractured Broke Fall Tons. in 5" Bend. Blows. Blows. In. A = 30.5 28 p. c. Good 61 78 12
In order to test the comparative value of steel of 243/4 up to 35 tons tensile strength, I had several specimens taken from shafts tested in the manner described, which may be called a fatigue test. The results are shown on the same sheet:
B = 241/2 Good 64 72 7 B — — — 48 54 12 C = 27 25.9 p. c. Good 76 81 12 D = 29.6 28.4 p. c. Good 71 78 12 E = 30.5 28.9 p. c. Good 58 77 12 F = 35.5 20 p. c. Good 80 91 12
The latter was very tough to break. Specimen marked A shows one of these pieces of steel. I show you also fresh broken specimens which will give you a good idea of the beautiful quality of this material. These specimens were cut out of shafts made of Steel Co. of Scotland's steel. I also show you specimens of cold bending:
Tensile Elong. Fractured Broke Fall Tons. in. 5" Bend. Blows. Blows. In. G = 30.9 271/2 p. c. Good 59 66 12 H = 29.3 30 p. c. Good 66 90 12 I = 28.9 28.9 p. c. Good 53 68 12
I think all of the above tests show that this material, when carefully made and treated with sufficient mechanical work on forging down from the ingot, is suitable up to 34 tons for crank shafts; how much higher it would be desirable to go is a question of superior excellence in material and manufacture resting with the makers. I would, however, remark that no allowance has been made by the Board of Trade or Lloyds for the excellence of this material above that of iron. I was interested to know how the material in the best iron shafts would stand this fatigue test compared with steel, and had some specimens of same dimensions cut out of iron shafts. The following are the results: Best iron, three good qualities, rolled into flat bars, cut and made into 41/2 cwt. blooms.
J = 18.6 24.3 p. c. Good 17 18 12
Made of best double rolled scrap, 41/2 cwt. blooms.
K = 22 321/2 p. c. Good 21 32 12
You will see from these results that steel stood this fatigue test, Vickers' 73 per cent. and Steel Co.'s 68 per cent., better than iron of the best quality for crank shafts; and I am of opinion that so long as we use such material as these for crank shafts, along with the present rules, and give ample bearing surface, there will be few broken shafts to record.
I omitted to mention that built shafts, both of steel and iron, of large diameter, are now in general use, and with the excellent machines, and under special mechanics, are built up of five separate pieces in such a rigid manner that they possess all the solidity necessary for a crank shaft. The forgings of iron and steel being much smaller are capable of more careful treatment in the process of manufacture. These shafts, for large mail steamers, when coupled up, are 35 feet long, and weigh 45 tons. They require to be carefully coupled, some makers finishing the bearings in the lathe, others depend on the excellence of their work in each piece, and finish each complete. To insure the correct centering of these large shafts, I have had 6 in. dia. recesses 3/4 inch deep turned out of each coupling to one gauge and made to fit one disk. Duplicate disks are then fitted in each coupling, and the centering is preserved, and should a spare piece be ever required, there is no trouble to couple correctly on board the steamer.
The propeller shaft is generally made of iron, and if made not less than the Board of Trade rules as regards diameter, of the best iron, and the gun metal liners carefully fitted, they have given little trouble; the principal trouble has arisen from defective fitting of the propeller boss. This shaft working in sea water, though running in lignum vitae bearings, has a considerable wear down at the outer bearings in four or five years, and the shaft gets out of line. This wear has been lessened considerably by fitting the wood so that the grain is endway to the shaft, and with sufficient bearing surface these bearings have not required lining up for nine years. It is, however, a shaft that cannot be inspected except when in dry dock, and has to be disconnected from the propeller, and drawn inside for examination at periods suggested by experience. Serious accidents have occurred through want of attention to the examination of this shaft; when working in salt water, with liners of gun metal, galvanic action ensues, and extensive corrosion takes place in the iron at the ends of the brass liners, more especially if they are faced up at right angles to the shaft. Some engineers have the uncovered part of the shaft between the liners, inside the tube, protected against the sea water by winding over it tarred line. As this may give out and cause some trouble, by stopping the water space, I have not adopted it, and shall be pleased to have the experience of any seagoing engineer on this important matter. A groove round the shaft is formed, due to this action, and in some cases the shaft has broken inside the stern tube, breaking not only it, but tearing open the hull, resulting in the foundering of the vessel. Steel has been used for screw shafts, but has not been found so suitable, as it corrodes more rapidly in the presence of salt water and gun metal than iron, and unless protected by a solid liner for the most part of its length, a mechanical feat which has not yet been achieved in ordinary construction, as this liner would require to be 20 ft. long. I find it exceedingly difficult to get a liner of only 7 ft. long in one piece, and the majority of 6 ft. liners are fitted in two pieces. The joint of the two liners is rarely watertight, and many shafts have been destroyed by this method of fitting these liners.
I trust that engine builders will make a step further in the fitting of these liners on these shafts, as it is against the interest of the shipowner to keep ships in dry dock from such causes as defective liners, and I think it will be only a matter of time when the screw shaft will be completely protected from sea water, at least inside the stern tube; and when this is done, I would have no hesitation in using steel for screw shafts. Though an easier forging than a crank shaft, these shafts are often liable to flaws of a very serious character, owing to the contraction of the mass of metal forming the coupling; the outside cooling first tears the center open, and when there is not much metal to turn off the face of the coupling, it is sometimes undiscovered. Having observed several of these cavities, some only when the last cut was being taken off, I have considered it advisable to have holes bored in the end and center of each coupling, as far through as the thickness of the flange; when the shafts are of large size, this is sure to find these flaws out. Another flaw, which has in many cases proved serious when allowed to extend, is situated immediately abaft the gun metal liner, in front of the propeller.
This may be induced by corrosion, caused by the presence of sea water, gun metal, and iron, assisted by the rotation of the shaft. It may also be caused under heavy strain, owing to the over-finishing of the shaft at this part under the steam hammer.
The forgemen, in these days of competition and low prices, are instructed to so finish that there won't be much weight to turn off when completing the shaft in the lathe. This is effected by the use of half-round blocks under the hammer, at a lower temperature than the rest of the forging is done, along with the use of a little water flung on from time to time; and it is remarkable how near a forging is in truth when centered in the lathe, and how little there is to come off. The effect of this manipulation is to form a hard ring of close grain about one inch thick from the circumference of the shaft inward. The metal in this ring is much harder than that in the rest of the shaft, and takes all the strain the inner section gives; consequently, when strain is brought on, either in heavy weather or should the propeller strike any object at sea or in the Suez canal, a fracture is caused at the circumference. This, assisted by slight corrosion, has in my experience led in the course of four months to a screw shaft being seriously crippled.
I show you a section of a screw shaft found to be flawed, and which I had broken under the falling weight of a steam hammer, when the decided difference of the granules near the circumference from that in the central part conveyed to me that it was weakened by treatment I have referred to. I think more material should be left on the forging, and the high finish with a little cold water should be discontinued. Doing away with the outer bearing in rudder post is an improvement, provided the bearing in the outer end of screw shaft in the stern tube is sufficiently large. It allows the rudder post to have its own work to do without bringing any strain on the screw shaft, and in the event of the vessel's grounding and striking under the rudder post, it does not throw any strain on the screw shaft. It also tends to reduce weight at this part, where all the weight is overhung from the stern of the vessel.
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EXPERIMENTAL AID IN THE DESIGN OF HIGH SPEED STEAMSHIPS.
By D. P.
The achievement of one triumph after another in the matter of high speed steamships, and especially the confidence with which pledges of certain results are given and accepted long before actual trials are made, form one of the most convincing proofs of the important part which scientific methods play in modern shipbuilding. This is evident in the case of ships embodying novel or hitherto untried features, and more especially so in cases where shipbuilders, having no personal practical experience or data, achieve such results. This was notably illustrated in the case of the Fairfield Co. undertaking some five years ago to build and engine a huge craft of most phenomenal form and proportions, and to propel the vessel at a given speed under conditions which appeared highly impracticable to many engaged in the same profession. The contract was proceeded with, however, and the Czar of Russia's wonderful yacht Livadia was the result, which (however much she may have justified the professional strictures as to form and proportions) entirely answered the designer's anticipations as to speed. Equally remarkable and far more interesting instances are the Inman liners City of Paris and City of New York, in whose design there was sufficient novelty to warrant the degree of misgiving which undoubtedly existed regarding the Messrs. Thomson's ability to attain the speed required. In the case at least of the City of Paris, Messrs. Thomson's intrepidity has been triumphantly justified. An instance still more opposite to our present subject is found in the now renowned Channel steamers Princess Henrietta and Princess Josephine, built by Messrs. Denny, of Dumbarton, for the Belgian government. The speed stipulated for in this case was 201/2 knots, and although in one or two previous Channel steamers, built by the Fairfield Co., a like speed had been achieved, still the guaranteeing of this speed by Messrs. Denny was remarkable, in so far as the firm had never produced, or had to do with, any craft faster than 15 or 16 knots. The attainment not only of the speed guaranteed, but of the better part of a knot in excess of that speed, was triumphant testimony to the skill and care brought to bear upon the undertaking. In this case, at least, the result was not one due to a previous course of "trial and error" with actual ships, but was distinctly due to superior practical skill, backed and enhanced by knowledge and use of specialized branches in the science of marine architecture. Messrs. Denny are the only firm of private shipbuilders possessing an experimental tank for recording the speed and resistance of ships by means of miniature reproductions of the actual vessels, and to this fact may safely be ascribed their confidence in guaranteeing, and their success in obtaining, a speed so remarkable in itself and so much in excess of anything they had previously had to do with. Confirmatory evidence of their success with the Belgian steamers is afforded by the fact that they have recently been instructed to build for service between Stranraer and Larne a paddle steamer guaranteed to steam 19 knots, and have had inquiries as to other high speed vessels.
In estimating the power required for vessels of unusual types or of abnormal speed, where empirical formulae do not apply, and where data for previous ships are not available, the system of experimenting with models is the only trustworthy expedient. In the case of the Czar's extraordinary yacht, the Livadia, already referred to, it may be remembered that previous to the work of construction being proceeded with, experiments were made with a small model of the vessel by the late Dr. Tideman, at the government tank at Amsterdam. On the strength of the data so obtained, coupled with the results of trials made with a miniature of the actual vessel on Loch Lomond, those responsible for her stipulated speed were satisfied that it could be attained. The actual results amply justified the reliance placed upon such experiments.
The design of many of her Majesty's ships has been altered after trials with their models. This was notably the case in connection with the design of the Medway class of river gunboats. The Admiralty constructors at first determined to make them 110 ft. long, by only 26 ft. in breadth. A doubt arising in their minds, the matter was referred to the late Mr. Froude, who had models made of various breadths, with which he experimented. The results satisfied the Admiralty officers that a substantial gain, rather than a loss, would follow from giving them much greater beam than had been proposed, and this was amply verified in the actual ships.
So long ago as the last decade of last century, an extended series of experiments with variously shaped bodies, ships as well as other shapes, were conducted by Colonel Beaufoy, in Greenland dock, London, under the auspices of a society instituted to improve naval architecture at that time. Robert Fulton, of America, David Napier, of Glasgow, and other pioneers of the steamship, are related to have carried out systematic model experiments, although of a rude kind in modern eyes, before entering on some of their ventures. About 1840 Mr. John Scott Russell carried on, on behalf of the British Association, of which he was at that time one of its most distinguished members, an elaborate series of investigations into the form of least resistance in vessels. For this purpose he leased the Virginia House and grounds, a former residence of Rodger Stewart, a famous Greenock shipowner of the early part of the century, the house being used as offices, while in the grounds an experimental tank was erected. In it tests were made of the speed and resistance of the various forms which Mr. Russell's ingenuity evolved—notably those based on the well-known stream line theory—as possible types of the steam fleets of the future. All the data derived from experiment was tabulated, or shown graphically in the form of diagrams, which, doubtless, proved of great interest to the savants of the British Association of that day. Mr. Russell returned to London in 1844, and the investigations were discontinued.
It will thus be seen that model experiments had been made by investigators long before the time of the late Dr. William Froude, of Torquay. It was not, however, until this gentleman took the subject of resistance of vessels in hand that designers were enabled to render the results from model trials accurately applicable to vessels of full size. This was principally due to his enunciation and verification by experiment of what is now known as the "law of comparison," or the law by which one is enabled to refer accurately the resistance of a model to one of larger size, or to that of a full sized vessel. In effect, the law is this—for vessels of the same proportional dimensions, or, as designers say, of the same lines, there are speeds appropriate to these vessels, which vary as the square roots of the ratio of their dimensions, and at these appropriate speeds the resistances will vary as the cubes of these dimensions. The fundament upon which the law is based has recently been shown to have found expression in the works of F. Reech, a distinguished French scientist who wrote early in the century. There are no valid grounds for supposing that the discovery of Reech was familiar to Froude; but even were this so, it is abundantly evident that, although never claimed by himself, there are the best of grounds for claiming the law of comparison, as now established, to be an independent discovery of Froude's.
Dr. Froude began his investigations with ships' models at the experimental tank at Torquay about 1872, carrying it on uninterruptedly until his death in 1879. Since his decease, the work of investigation has been carried on by his son, Mr. R. E. Froude, who ably assisted his father, and originated much of the existing apparatus. At the beginning of 1886, the whole experimental appliances and effects were removed from Torquay to Haslar, near Portsmouth, where a large tank and more commodious offices have been constructed, with a view to entering more extensively upon the work of experimental investigation. The dimensions of the old tank were 280 ft. in length, 36 ft. in width, and 10 ft. in depth. The new one is about 400 ft. long, 20 ft. wide, and 9 ft. deep. The new establishment is more commodious and better equipped than the old, and although the experiments are taken over a greater length, the operators are enabled to turn out results with as great dispatch as in the Torquay tank. The adjacency of the new tank to the dockyard at Portsmouth enables the Admiralty authorities to make fuller and more frequent use of it than formerly. Since the value of the work carried on for the British government has become appreciated, several experimental establishments of a similar character have been instituted in other countries. The Dutch government in 1874 formed one at Amsterdam which, up till his death in 1883, was under the superintendence of Dr. Tideman, whose labors in this direction were second only to those of the late Dr. Froude. In 1877 the French naval authorities established an experimental tank in the dockyard at Brest, and the Italian government have just completed one on an elaborate scale in the naval dockyard at Spezia. The Spezia tank, which is 500 ft. in length by about 22 ft. in breadth, is fully equipped with all the special and highly ingenious instruments and appliances which the scientific skill of the late Dr. Froude brought into existence, and have been since his day improved upon by his son, Mr. R. E. Froude, and other experts.
Through the courtesy of our own Admiralty and of Messrs. Denny, of Dumbarton, the Italians have been permitted to avail themselves of the latest improvements which experience has suggested, and the construction of the special machinery and apparatus required has been executed by firms in this country having previous experience in this connection—Messrs. Kelso & Co., of Commerce Street, Glasgow; and Mr. Robert W. Munro, of London.
Having briefly traced the origin and development of the system of model experiment, it may now be of interest to describe the modus operandi of such experiments, and explain the way in which they are made applicable to actual ships. The models with which experiments are made in those establishments conducted on the lines instituted by Mr. Froude are made of paraffin wax, a material well adapted for the purpose, being easily worked, impervious to water, and yielding a fine smooth surface. Moreover, when done with, the models may be remelted for further use and all parings utilized. They are produced in the following manner: A mould is formed in clay by means of cross sections made somewhat larger than is actually required, this allowance being made to admit of the cutting and paring afterward required to bring the model to the correct point. Into this mould a core is placed, consisting of a light wooden framework covered with calico and coated with a thick solution of clay to make it impervious to the melted paraffin. This latter substance is run into the space between the core and the mould and allowed to cool. This space, forming the thickness of the model, is usually from 3/4 in. for a model of 10 ft. long to 11/4 in. and 11/2 in. for one of 16 ft. and 18 ft. long. When cold, the model is floated out of the mould by water pressure and placed bottom upward on the bed of a shaping machine, an ingenious piece of mechanism devised by the late Dr. Froude, to aid in reducing the rough casting to the accurate form. The bed of this machine, which travels automatically while the machine is in operation, can be raised or lowered to any desired level by adjusting screws. A plan of water lines of the vessel to be modeled is placed on a tablet geared to the machine, the travel of which is a function of the travel of the bed containing the model. With a pointer, which is connected by a system of levers to the cutting tools, the operator traces out the water lines upon the plan as the machine and its bed are in motion, with the result that corresponding lines are cut upon the model. The cutting tools are swiftly revolving knives which work on vertical spindles moved in a lateral direction (brought near or removed from each other), according to the varying breadth of the water lines throughout the length of the model, as traced out by the operator's pointer. In this way a series of longitudinal incisions are made on the model at different levels corresponding to the water lines of the vessel. The model is now taken from the bed of the machine and the superfluous material or projection between the incisions is removed by means of a spokeshave or other sharp hand tool, and the whole surface brought to the correct form, and made fair and smooth.
To test accuracy of form, the weight of model is carefully taken, and the displacement at the intended trial draught accurately determined from the plan of lines. The difference between the weight of model and the displacement at the draught intended is then put into the bottom of the model in the form of small bags of shot, and by unique and very delicately constructed instruments for ascertaining the correct draught, the smallest error can at once be detected and allowed for. The models vary in size from about one-tenth to one-thirtieth of the size of the actual ship. A model of the largest size can be produced and its resistance determined at a number of speeds in about two days or so. The mode of procedure in arranging the model for the resistance experiment, after the model is afloat in the tank at the correct draught and trim, consists in attaching to it a skillfully devised dynamometric apparatus secured to a lightly constructed carriage. This carriage traverses a railway which extends the whole length of the tank about 15 in. or 18 in. above the water. The floating model is carefully guided in its passage through the water by a delicate device, keeping it from deviating either to the right or left, but at the same time allowing a free vertical and horizontal motion. The carriage with the model attached is propelled by means of an endless steel wire rope, passing at each end of the tank around a drum, driven by a small stationary engine, fitted with a very sensitive governor, capable of being so adjusted that any required speed may be given to the carriage and model. The resistance which the model encounters in its passage through the water is communicated to a spiral spring, and the extension this spring undergoes is a measure of the model's resistance. The amount of the extension is recorded on a revolving cylinder to a much enlarged scale through the medium of levers or bell cranks supported by steel knife edges resting on rocking pieces. On the same cylinder are registered "time" and "distance" diagrams, by means of which a correct measure of the speed is obtained. The time diagram is recorded by means of a clock attached to an electric circuit, making contact every half second, and actuating a pen which forms an indent in what would otherwise be a straight line on the paper. The distance pen, by a similar arrangement, traces another line on the cylinder in which are indents corresponding to fixed distances of travel along the tank, the indents being caused by small projections which strike a trigger at the bottom of the carriage as it passes, and make electric contact. From these time and distance diagrams accurate account can be taken of the speed at which the model and its supporting carriage have been driven. Thus on the same cylinder is recorded graphically the speed and resistance of the model. The carriage may be driven at any assigned speed by adjusting the governor of the driving engine already alluded to, but the record of the speed by means of the time and distance diagrams is more definite. When the resistances of the model have been obtained at several speeds, varying in some cases from 50 to 1,000 feet per minute, the speeds are set off in suitable units along a base line, and for every speed at which resistance is measured, the resistance is set off to scale as an ordinate value at those speeds. A line passing through these spots forms the "curve of resistance," from which the resistance experienced by the model at the given trial speeds or any intermediate speed can be ascertained. The resistance being known, the power required to overcome resistance and drive the actual ship at any given speed is easily deduced by applying the rule before described as the law of comparison.—The Steamship.
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THE SHIP IN THE NEW FRENCH BALLET OF THE "TEMPEST."
A new ballet, entitled the "Tempest," by Messrs. Barbier and Thomas, has recently been put upon the stage of the Opera at Paris with superb settings. One of the most important of the several tableaux exhibited is the last one of the third act, in which appears a vessel of unusual dimensions for the stage, and which leaves far behind it the celebrated ships of the "Corsaire" and "L'Africaine." This vessel, starting from the back of the stage, advances majestically, describes a wide circle, and stops in front of the prompter's box.
As the structure of this vessel and the mechanism by which it is moved are a little out of the ordinary, we shall give some details in regard to them. First, the sea is represented by four parallel strips of water, each formed of a vertical wooden frame entirely free in its movements (Fig. 2). The ship (Figs. 1, 2, 3, 4 and 5) is carried by wheels that roll over the floor of the stage. It is guided in its motion by two grooved bronze wheels and by a rail formed of a simple reversed T-iron which is fixed to the floor by bolts. In measure as it advances, the strips of water open in the center to allow it to pass, and, as the vessel itself is covered up to the water line with painted canvas imitating the sea, it has the appearance of cleaving the waves. As soon as it has passed, the three strips of water in the rear rise slightly. When the vessel reaches the first of the strips, the three other strips, at first juxtaposed against the preceding, spread out and thus increase the extent of the sea, while the inclined plane of the preceding tableau advances in order to make place for the vessel. The shifting of this inclined place is effected by simply pulling upon the carpet that covers it, and which enters a groove in the floor in front of the prompter's box. At this moment, the entire stage seems to be in motion, and the effect is very striking.
We come now to the details of construction of the vessel. It is not here a question of a ship represented simply by means of frames and accessories, but of a true ship in its entirety, performing its evolutions over the whole stage. Now, a ship is not constructed at a theater as in reality. It does not suffice to have it all entire upon the stage, but it is necessary also to be able to dismount it after every representation, and that, too, in a large number of pieces that can be easily stored away. Thus, the vessel of the Tempest, which measures a dozen yards from stem to stern, and is capable of carrying fifty persons, comes apart in about 250 pieces of wood, without counting all the iron work, bolts, etc. Nevertheless, it can be mounted in less than two hours by ten skilled men.
The visible hull of the ship is placed upon a large and very strong wooden framework, formed of twenty-six trusses. In the center, there are two longitudinal trusses about three feet in height by twenty-five in length, upon which are assembled, perpendicularly, seven other trusses. In the interior there are six transverse pieces held by stirrup bolts, and at the extremity of each of these is fixed a thirteen-inch iron wheel. It is upon these twelve wheels that the entire structure rolls.
There are in addition the two bronze guide wheels that we have already spoken of. In the rear there are two large vertical trusses sixteen feet in height, which are joined by ties and descend to the bottom of the frame, to which they are bolted. These are worked out into steps and constitute the skeleton of the immense stern of the vessel. The skeleton of the prow is formed of a large vertical truss which is bolted to the front of the frame and is held within by a tie bar. On each side of this truss are placed the parallels (Figs. 1 and 3), which are formed of pieces of wood that are set into the frame below and are provided above with grooves for the passage of iron rods that support the foot rests by means of which the supernumeraries are lifted. As a whole, those rods constitute a jointed parallelogram, so that the foot rest always remains horizontal while describing a curve of five feet radius from the top of the frame to the deck of the vessel. They are actuated by a cable which winds around a small windlass fixed in the interior of the frame.
The large mast consists of a vertical sheath 10 ft. high, which is set into the center of the frame, and in the interior of which slides a wooden spar that exceeds it by 5 ft. at first, and is capable of being drawn out as many more feet for the final apotheosis. This part of the mast carries three footboards and a platform for the reception of "supers." It is actuated by a windlass placed upon the frame.
To form the skeleton of the vessel there are mounted upon the frame a series of eight large vertical trusses parallel with each other and cross-braced by small trusses. The upper part of these supports the flooring of the deck, and their exterior portion affects the curve of a ship's sides. It is to these trusses that are attached the panels covered with painted canvas that represent the hull. These panels are nine in number on each side. Above are placed those that simulate the nettings and those that cover the prow or form its crest.
The turret that surrounds the large mast is formed of vertical trusses provided with panels of painted canvas and carrying a floor for the figurants to stand upon.
The bowsprit is in two parts, one sliding in the other. The front portion is at first pulled back, in order to hide the vessel entirely in the side scenes. It begins to make its appearance before the vessel itself gets under way. Light silken cordages connect the mast, the bowsprit, and the small mast at the stern.
On each side of the vessel, there are bolted to the frame that supports it five iron frames covered with canvas (Fig. 3), which reach the level of the water line, and upon which stand the "supers" representing the naiads that are supposed to draw the ship upon the beach. Finally at the bow there is fixed a frame which supports a danseuse representing the living prow of the vessel.
The vessel is drawn to the middle of the stage by a cable attached to its right side and passing around a windlass placed in the side scenes to the left (Fig. 2). It is at the same time pushed by machinists placed in the interior of the framework. The latter, as above stated, is entirely covered with painted canvas resembling water.
As the vessel, freighted with harmoniously grouped spirits, and with naiads, sea fairies, and graceful genii seeming to swim around it, sails in upon the stage, puts about, and advances as if carried along by the waves to the front of the stage, the effect is really beautiful, and does great credit to the machinists of the Opera.
We are indebted to Le Genie Civil and Le Monde Illustre for the description and engravings.
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THE GIRARD HYDRAULIC RAILWAY.
We give herewith some illustrations of this railway which has recently excited so much technical interest in Europe and America, and which threatens to revolutionize both the method and velocity of traveling, if only the initial expense of laying the line can be brought within moderate limits. A short line of railway has been laid in Paris, and we have there examined it, and traveled over the line more than once; so that we can testify to the smoothness and ease of the motion. Sir Edward Watkin examined the railway recently, and we understand that a line two miles long is to be laid in London, under his auspices. He seems to think it might be used for the Channel tunnel, being both smokeless and noiseless. It might also, if it could be laid at a sufficiently low price, be useful for the underground railways in London, of one of which he is chairman. We are favorably impressed by the experiments we have witnessed; our misgivings are as to the cost. The railway is the invention of the well known hydraulic engineer, Monsieur Girard, who, as early as 1852, endeavored to replace the ordinary steam traction on railways by hydraulic propulsion, and in 1854 sought to diminish the resistance to the movement of the wagons by removing the wheels, and causing them to slide on broad rails. In order to test the invention, Mons. Girard demanded, and at the end of 1869 obtained, a concession for a short line from Paris to Argenteuil, starting in front of the Palais de l'Industrie, passing by Le Champ de Courses de Longchamps, and crossing the Seine at Suresnes. Unfortunately, the war of 1870-71 intervened, during which the works were destroyed and Mons. Girard was killed. After his death the invention was neglected for some years. A short time ago, however, one of his former colleagues, Mons. Barre, purchased the plans and drawings of Mons. Girard from his family, and having developed the invention, and taken out new patents, formed a company to work them. The invention may be divided into two parts, which are distinct, the first relating to the mode of supporting the carriages and the second to their propulsion. Each carriage is carried by four or six shoes, shown in Figs. 3, 4, and 5; and these shoes slide on a broad, flat rail, 8 in. or 10 in. wide. The rail and shoe are shown in section in Fig. 1. The rail is bolted to longitudinal wooden sleepers, and the shoe is held on the rail by four pieces of metal, A, two on each side, which project slightly below the top of the rail. The bottom of the shoe which is in contact with the rail is grooved or channeled, so as to hold the water and keep a film between each shoe and the rail. The carriage is supported by vertical rods, which fit one into each shoe, a hole being formed for that purpose; and the point of support being very low, and quite close to the rail, great stability is insured. It is proposed to make the rail of the form shown in Fig. 2 in future, as this will avoid the plates, A, and the flanges, B, will help to keep the water on the rail. Figs. 3, 4, and 5 show the shoe in detail. Fig. 3 gives a longitudinal section, Fig. 4 is a plan, and Fig. 5 is a plan of the shoe inverted, showing the grooves in its face. Fig. 3 shows the hollow shoe, into which water at a pressure of ten atmospheres is forced by a pipe from a tank on the tender. The water enters by the pipe, C, and fills the whole of the chamber, D. The water attempts to escape, and in doing so lifts the shoe slightly, thus filling the first groove of the chamber. The pressure again lifts the shoe, and the second chamber is filled; and so on, until ultimately the water escapes at the ends, E, and sides, F. Thus a film of water is kept between the shoe and the rail, and on this film the carriage is said to float. The water runs away into the channels, H H (Fig. 6), and is collected to be used over again. Fig. 3 also shows the means of supporting the carriage on the shoe by means of K, the point of support being very low. The system of grooves on the lower face of the shoe is shown in Fig. 5. So much for the means by which wheels are dispensed with, and the carriage enabled to slide along the line.
The next point is the method of propulsion. Figs. 7 and 8 give an elevation and plan of one of the experimental carriages. Along the under side of each of the carriages a straight turbine, L L, extends the whole length, and water at high pressure impinges on the blades of this turbine from a jet, M, and by this means the carriage is moved along. A parabolic guide, which can be moved in and out of gear by a lever, is placed under the tender, and this on passing strikes the tappet, S, and opens the valve which discharges the water from the jet, M, and this process is repeated every few yards along the whole line. The jets, M, must be placed at such a distance apart that at least one will be able to operate on the shortest train that can be used. In this turbine there are two sets of blades, one above the other, placed with their concave sides in opposite directions, so that one set is used for propelling in one direction and the other in the opposite direction. In Fig. 6 it is seen that the jet, M, for one direction is just high enough to act against the blades, Q, while the other jet is higher, and acts on the blades, P, for propulsion in the opposite direction. The valves, R, which are opened by the tappet, S, are of peculiar construction, and we hope soon to be able to give details of them. Reservoirs (Fig. 6) holding water at high pressure must be placed at intervals, and the pipe, T, carrying high pressure water must run the whole length of the line. Fig. 6 shows a cross section of the rail and carriage, and gives a good idea of the general arrangements. The absence of wheels and of greasing and lubricating arrangements will alone effect a very great saving, as we are informed that on the Lyons Railway, which is 800 kilometers long, the cost of oil and grease exceeds L400,000 per annum. As Sir Edward Watkin recently explained, all the great railway companies have long tried to find a substitute for wheels, and this railway appears to offer a solution of that problem. Mons. Barre thinks that a speed of 200 kilometers (or 120 miles) per hour may be easily and safely attained.
Of course, as there is no heavy locomotive, and as the traction does not depend upon pressure on the rail, the road may be made comparatively light. The force required to move a wagon along the road is very small, Mons. Barre stating, as the result of his experiments, that an effort amounting to less than half a kilogramme is sufficient to move one ton when suspended on a film of water with his improved shoes. It is recommended that the stations be placed at the summit of a double incline, so that on going up one side of the incline the motion of the train may be arrested, and on starting it may be assisted. No brakes are required, as the friction of the shoe against the rail, when the water under pressure is not being forced through, is found to be quite sufficient to bring the train to a standstill in a very short distance. The same water is run into troughs by the side of the line, and can be used over and over again indefinitely, and in the case of long journeys, the water required for the tender could be taken up while the train is running. The principal advantages claimed for the railway are: The absence of vibration and of side rolling motion; the pleasure of traveling is comparable to that of sleighing over a surface of ice, there is no noise, and what is important in town railways, no smoke; no dust is caused by the motion of the train during the journey. It is not easy for the carriages to be thrown from the rails, since any body getting on the rail is easily thrown off by the shoe, and will not be liable to get underneath, as is the case with wheels; the train can be stopped almost instantly, very smoothly, and without shock. Very high speed can be attained; with water at a pressure of 10 kilogrammes, a speed of 140 kilometers per hour can be attained; great facility in climbing up inclines and turning round the curves; as fixed engines are employed to obtain the pressure, there is great economy in the use of coal and construction of boilers, and there is a total absence of the expense of lubrication. It is, however, difficult to see how the railway is to work during a long and severe frost. We hope to give further illustrations at an early date of this remarkable invention.—Industries.
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[Footnote 1: Lecture delivered at the Royal Institution, on Friday, June 14, by Mr. C. V. Boys, F.R.S.—Nature.]
In almost all investigations which the physicist carries out in the laboratory, he has to deal with and to measure with accuracy those subtile and to our senses inappreciable forces to which the so-called laws of nature give rise. Whether he is observing by an electrometer the behavior of electricity at rest or by a galvanometer the action of electricity in motion, whether in the tube of Crookes he is investigating the power of radiant matter, or with the famous experiment of Cavendish he is finding the mass of the earth—in these and in a host of other cases he is bound to measure with certainty and accuracy forces so small that in no ordinary way could their existence be detected, while disturbing causes which might seem to be of no particular consequence must be eliminated if his experiments are to have any value. It is not too much to say that the very existence of the physicist depends upon the power which he possesses of producing at will and by artificial means forces against which he balances those that he wishes to measure.
I had better perhaps at once indicate in a general way the magnitude of the forces with which we have to deal.
The weight of a single grain is not to our senses appreciable, while the weight of a ton is sufficient to crush the life out of any one in a moment. A ton is about 15,000,000 grains. It is quite possible to measure with unfailing accuracy forces which bear the same relation to the weight of a grain that a grain bears to a ton.
To show how the torsion of wires or threads is made use of in measuring forces, I have arranged what I can hardly dignify by the name of an experiment. It is simply a straw hung horizontally by a piece of wire. Resting on the straw is a fragment of sheet iron weighing ten grains. A magnet so weak that it cannot lift the iron yet is able to pull the straw round through an angle so great that the existence of the feeble attraction is evident to every one in the room.
Now it is clear that if, instead of a straw moving over the table simply, we had here an arm in a glass case and a mirror to read the motion of the arm, it would be easy to observe a movement a hundred or a thousand times less than that just produced, and therefore to measure a force a hundred or a thousand times less than that exerted by this feeble magnet.
Again, if instead of wire as thick as an ordinary pin I had used the finest wire that can be obtained, it would have opposed the movement of the straw with a far less force. It is possible to obtain wire ten times finer than this stubborn material, but wire ten times finer is much more than ten times more easily twisted. It is ten thousand times more easily twisted. This is because the torsion varies as the fourth power of the diameter. So we say 10 x 10 = 100, 100 x 100 = 10,000. Therefore, with the finest wire, forces 10,000 times feebler still could be observed.
It is therefore evident how great is the advantage of reducing the size of a torsion wire. Even if it is only halved, the torsion is reduced sixteenfold. To give a better idea of the actual sizes of such wires and fibers as are in use, I shall show upon the screen a series of such photographs taken by Mr. Chapman, on each of which a scale of thousandths of an inch has been printed.
The first photograph (Fig. 1) is an ordinary hair—a sufficiently familiar object, and one that is generally spoken of as if it were rather fine. Much finer than this is the specimen of copper wire now on the screen (Fig. 2), which I recently obtained from Messrs. Nalder Brothers. It is only a little over one-thousandth of an inch in diameter. Ordinary spun glass, a most beautiful material, is about one-thousandth of an inch in diameter, and this would appear to be an ideal torsion thread (Fig. 3). Owing to its fineness, its torsion would be extremely small, and the more so because glass is more easily deformed than metals. Owing to its very great strength, it can carry heavier loads than would be expected of it. I imagine many physicists must have turned to this material in their endeavor to find a really delicate torsion thread. I have so turned only to be disappointed. It has every good quality but one, and that is its imperfect elasticity. For instance, a mirror hung by a piece of spun glass is casting an image of a spot of light on the scale. If I turn the mirror, by means of a fork, twice to the right, and then turn it back again, the light does not come back to its old point of rest, but oscillates about a point on one side, which, however, is slowly changing, so that it is impossible to say what the point of rest really is. Further, if the glass is twisted one way first and then the other way, the point of rest moves in a manner which shows that it is not influenced by the last deflection alone: the glass remembers what was done to it previously. For this reason spun glass is quite unsuitable as a torsion thread; it is impossible to say what the twist is at any time, and therefore what is the force developed.
So great has the difficulty been in finding a fine torsion thread that the attempt has been given up, and in all the most exact instruments silk has been used. The natural cocoon fibers, as shown on the screen (Fig. 4), consist of two irregular lines gummed together, each about one two-thousandth of an inch in diameter. These fibers must be separated from one another and washed. Then each component will, according to the experiment of Gray, carry nearly 60 grains before breaking, and can be safely loaded with 15 grains. Silk is therefore very strong, carrying at the rate of from 10 to 20 tons to the square inch. It is further valuable in that its torsion is far less than that of a fiber of the same size of metal or even of glass, if such could be produced. The torsion of silk, though exceedingly small, is quite sufficient to upset the working of any delicate instrument, because it is never constant. At one time the fiber twists one way and another time in another, and the evil effect can only be mitigated by using large apparatus in which strong forces are developed. Any attempt that may be made to increase the delicacy of apparatus by reducing their dimensions is at once prevented by the relatively great importance of the vagaries of the silk suspension.
The result, then, is this. The smallness, the length of period, and therefore delicacy, of the instruments at the physicist's disposal have until lately been simply limited by the behavior of silk. A more perfect suspension means still more perfect instruments, and therefore advance in knowledge.
It was in this way that some improvements that I was making in an instrument for measuring radiant heat came to a deadlock about two years ago. I would not use silk, and I could not find anything else that would do. Spun glass, even, was far too coarse for my purpose, it was a thousand times too stiff.
There is a material invented by Wollaston long ago, which, however, I did not try because it is so easily broken. It is platinum wire which has been drawn in silver, and finally separated by the action of nitric acid. A specimen about the size of a single line of silk is now on the screen, showing the silver coating at one end (Fig. 5).
As nothing that I knew of could be obtained that would be of use to me, I was driven to the necessity of trying by experiment to find some new material. The result of these experiments was the development of a process of almost ridiculous simplicity which it may be of interest for me to show.
The apparatus consists of a small crossbow, and an arrow made of straw with a needle point. To the tail of the arrow is attached a fine rod of quartz which has been melted and drawn out in the oxyhydrogen jet. I have a piece of the same material in my hand, and now after melting their ends and joining them together, an operation which produces a beautiful and dazzling light, all I have to do is to liberate the string of the bow by pulling the trigger with one foot, and then if all is well a fiber will have been drawn by the arrow, the existence of which can be made evident by fastening to it a piece of stamp paper.
In this way threads can be produced of great length, of almost any degree of fineness, of extraordinary uniformity, and of enormous strength. I do not believe, if any experimentalist had been promised by a good fairy that he might have anything he desired, that he would have ventured to ask for any one thing with so many valuable properties as these fibers possess. I hope in the course of this evening to show that I am not exaggerating their merits.
In the first place, let me say something about the degree of fineness to which they can be drawn. There is now projected upon the screen a quartz fiber one five-thousandth of an inch in diameter (Fig. 6). This is one which I had in constant use in an instrument loaded with about 30 grains. It has a section only one-sixth of that of a single line of silk, and it is just as strong. Not being organic, it is in no way affected by changes of moisture and temperature, and so it is free from the vagaries of silk which give so much trouble. The piece used in the instrument was about 16 inches long. Had it been necessary to employ spun glass, which hitherto was the finest torsion material, then, instead of 16 inches, I should have required a piece 1,000 feet long, and an instrument as high as the Eiffel tower to put it in.
There is no difficulty in obtaining pieces as fine as this yards long if required, or in spinning it very much finer. There is upon the screen a single line made by the small garden spider, and the size of this is perfectly evident (Fig. 7). You now see a quartz fiber far finer than this, or, rather, you see a diffraction phenomenon, for no true image is formed at all; but even this is a conspicuous object in comparison with the tapering ends, which it is absolutely impossible to trace in a microscope. The next two photographs, taken by Mr. Nelson, whose skill and resources are so famous, represent the extreme end of a tail of quartz, and, though the scale is a great deal larger than that used in the other photographs, the end will be visible only to a few. Mr. Nelson has photographed here what it is absolutely impossible to see. What the size of these ends may be, I have no means of telling. Dr. Royston Piggott has estimated some of them at less than one-millionth of an inch, but, whatever they are, they supply for the first time objects of extreme smallness the form of which is certainly known, and, therefore, I cannot help looking upon them as more satisfactory tests for the microscope than diatoms and other things of the real shape of which we know nothing whatever.
Since figures as large as a million cannot be realized properly, it may be worth while to give an illustration of what is meant by a fiber one-millionth of an inch in diameter.
A piece of quartz an inch long and an inch in diameter would, if drawn out to this degree of fineness, be sufficient to go all the way round the world 658 times; or a grain of sand just visible—that is, one-hundredth of an inch long and one hundredth of an inch in diameter—would make one thousand miles of such thread. Further, the pressure inside such a thread due to a surface tension equal to that of water would be 60 atmospheres.
Going back to such threads as can be used in instruments, I have made use of fibers one ten-thousandth of an inch in diameter, and in these the torsion is 10,000 times less than that of spun glass.
As these fibers are made finer their strength increases in proportion to their size, and surpasses that of ordinary bar steel, reaching, to use the language of engineers, as high a figure as 80 tons to the inch. Fibers of ordinary size have a strength of 50 tons to the inch.
While it is evident that these fibers give us the means of producing an exceedingly small torsion, and one that is not affected by weather, it is not yet evident that they may not show the same fatigue that makes spun glass useless. I have, therefore, a duplicate apparatus with a quartz fiber, and you will see that the spot of light comes back to its true place on the screen after the mirror has been twisted round twice.
I shall now for a moment draw your attention to that peculiar property of melted quartz that makes threads such as I have been describing a possibility. A liquid cylinder, as Plateau has so beautifully shown, is an unstable form. It can no more exist than can a pencil stand on its point. It immediately breaks up into a series of spheres. This is well illustrated in that very ancient experiment of shooting threads of resin electrically. When the resin is hot, the liquid cylinders, which are projected in all directions, break up into spheres, as you see now upon the screen. As the resin cools, they begin to develop tails; and when it is cool enough, i.e., sufficiently viscous, the tails thicken and the beads become less, and at last uniform threads are the result. The series of photographs show this well.
There is a far more perfect illustration which we have only to go into the garden to find. There we may see in abundance what is now upon the screen—the webs of those beautiful geometrical spiders. The radial threads are smooth like the one you saw a few minutes ago, but the threads that go round and round are beaded. The spider draws these webs slowly, and at the same time pours upon them a liquid, and still further to obtain the effect of launching a liquid cylinder in space he, or rather she, pulls it out like the string of a bow, and lets it go with a jerk. The liquid cylinder cannot exist, and the result is what you now see upon the screen (Fig. 8). A more perfect illustration of the regular breaking up of a liquid cylinder it would be impossible to find. The beads are, as Plateau showed they ought to be, alternately large and small, and their regularity is marvelous. Sometimes two still smaller beads are developed, as may be seen in the second photograph, thus completely agreeing with the results of Plateau's investigations.
I have heard it maintained that the spider goes round her web and places these beads there afterward. But since a web with about 360,000 beads is completed in an hour—that is at the rate of about 100 a second—this does not seem likely. That what I have said is true, is made more probable by the photograph of a beaded web that I have made myself by simply stroking a quartz fiber with a straw wetted with castor oil (Fig. 9); it is rather larger than a spider line; but I have made beaded threads, using a fine fiber, quite indistinguishable from a real spider web, and they have the further similarity that they are just as good for catching flies.
Now, going back to the melted quartz, it is evident that if it ever became perfectly liquid, it could not exist as a fiber for an instant. It is the extreme viscosity of quartz, at the heat even of an electric arc, that makes these fibers possible. The only difference between quartz in the oxyhydrogen jet and quartz in the arc is that in the first you make threads and in the second are blown bubbles. I have in my hand some microscopic bubbles of quartz showing all the perfection of form and color that we are familiar with in the soap bubble.
An invaluable property of quartz is its power of insulating perfectly, even in an atmosphere saturated with water. The gold leaves now diverging were charged some time before the lecture, and hardly show any change, yet the insulator is a rod of quartz only three-quarters of an inch long, and the air is kept moist by a dish of water. The quartz may even be dipped in the water and replaced with the water upon it without any difference in the insulation being observed.
Not only can fibers be made of extreme fineness, but they are wonderfully uniform in diameter. So uniform are they that they perfectly stand an optical test so severe that irregularities invisible in any microscope would immediately be made apparent. Every one must have noticed when the sun is shining upon a border of flowers and shrubs how the lines which spiders use as railways to travel from place to place glisten with brilliant colors. These colors are only produced when the fibers are sufficiently fine. If you take one of these webs and examine it in the sunlight, you will find that the colors are variegated, and the effect, consequently, is one of great beauty.
A quartz fiber of about the same size shows colors in the same way, but the tint is perfectly uniform on the fiber. If the color of the fiber is examined with a prism, the spectrum is found to consist of alternate bright and dark bands. Upon the screen are photographs taken by Mr. Briscoe, a student in the laboratory at South Kensington, of the spectra of some of these fibers at different angles of incidence. It will be seen that coarse fibers have more bands than fine, and that the number increases with the angle of incidence of the light. There are peculiarities in the march of the bands as the angle increases which I cannot describe now. I may only say that they appear to move not uniformly, but in waves, presenting very much the appearance of a caterpillar walking.
So uniform are the quartz fibers that the spectrum from end to end consists of parallel bands. Occasionally a fiber is found which presents a slight irregularity here and there. A spider line is so irregular that these bands are hardly observable; but, as the photograph on the screen shows, it is possible to trace them running up and down the spectrum when you know what to look for.
To show that these longitudinal bands are due to the irregularities, I have drawn a taper piece of quartz by hand, in which the two edges make with one another an almost imperceptible angle, and the spectrum of this shows the gradual change of diameter by the very steep angle at which the bands run up the spectrum.
Into the theory of the development of these bands I am unable to enter; that is a subject on which your professor of natural philosophy is best able to speak. Perhaps I may venture to express the hope, as the experimental investigation of this subject is now rendered possible, that he may be induced to carry out a research for which he is so eminently fitted.
Though this is a subject which is altogether beyond me, I have been able to use the results in a practical way. When it is required to place into an instrument a fiber of any particular size, all that has to be done is to hold the frame of fibers toward a bright and distant light, and look at them through a low-angled prism. The banded spectra are then visible, and it is the work of a moment to pick out one with the number of bands that has been found to be given by a fiber of the desired size. A coarse fiber may have a dozen or more, while such fibers as I find most useful have only two dark bands. Much finer ones exist, showing the colors of the first order with one dark band; and fibers so fine as to correspond to the white or even the gray of Newton's scale are easily produced.
Passing now from the most scientific test of the uniformity of these fibers, I shall next refer to one more homely. It is simply this: The common garden spider, except when very young, cannot climb up one of the same size as the web on which she displays such activity. She is perfectly helpless, and slips down with a run. After vainly trying to make any headway, she finally puts her hands (or feet) into her mouth and then tries again, with no better success. I may mention that a male of the same species is able to run up one of these with the greatest ease, a feat which may perhaps save the lives of a few of these unprotected creatures when quartz fibers are more common.
It is possible to make any quantity of very fine quartz fiber without a bow and arrow at all, by simply drawing out a rod of quartz over and over again in a strong oxyhydrogen jet. Then, if a stand of any sort has been placed a few feet in front of the jet, it will be found covered with a maze of thread, of which the photograph on the screen represents a sample. This is hardly distinguishable from the web spun by this magnificent spider in corners of greenhouses and such places. By regulating the jet and the manipulation, anything from one of these stranded cables to a single ultro-microscope line may be developed.
And now that I have explained that these fibers have such valuable properties, it will no doubt be expected that I should perform some feat with their aid which, up to the present time, has been considered impossible, and this I intend to do.
Of all experiments, the one which has most excited my admiration is the famous experiment of Cavendish, of which I have a full size model before you. The object of this experiment is to weigh the earth by comparing directly the force with which it attracts things with that due to large masses of lead. As is shown by the model, any attraction which these large balls exert on the small ones will tend to deflect this 6 ft. beam in one direction, and then if the balls are reversed in position, the deflection will be in the other direction. Now, when it is considered how enormously greater the earth is than these balls, it will be evident that the attraction due to them must be in comparison excessively small. To make this evident, the enormous apparatus you see had to be constructed, and then, using a fine torsion wire, a perfectly certain but small effect was produced. The experiment, however, could only be successfully carried out in cellars and underground places, because changes of temperature produced effects greater than those due to gravity.
[Footnote 2: Dr. Lodge has been able, by an elaborate arrangement of screens, to make this attraction just evident to an audience.—C. V. B.]
Now I have in a hole in the wall an instrument no bigger than a galvanometer, of which a model is on the table. The balls of the Cavendish apparatus, weighing several hundredweight each, are replaced by balls weighing 13/4 pounds only. The smaller balls of 13/4 pounds are replaced by little weights of 15 grains each. The 6 foot beam is replaced by one that will swing round freely in a tube three-quarters of an inch in diameter. The beam is, of course, suspended by a quartz fiber. With this microscopic apparatus, not only is the very feeble attraction observable, but I can actually obtain an effect eighteen times as great as that given by the apparatus of Cavendish, and what is more important, the accuracy of observation is enormously increased.
The light from a lamp passes through a telescope lens, and falls on the mirror of the instrument. It is reflected back to the table, and thence by a fixed mirror to the scale on the wall, where it comes to a focus. If the mirror on the table were plane, the whole movement of the light would be only about eight inches, but the mirror is convex, and this magnifies the motion nearly eight times. At the present moment the attracting weights are in one extreme position, and the line of light is quiet. I will now move them to the other position, and you will see the result—the light slowly begins to move, and slowly increases in movement. In forty seconds it will have acquired its highest velocity, and in forty more it will have stopped at 5 feet 81/2 inches from the starting point, after which it will slowly move back again, oscillating about its new position of rest.
It is not possible at this hour to enter into any calculations; I will only say that the motion you have seen is the effect of a force of less than one ten-millionth of the weight of a grain, and that with this apparatus I can detect a force two thousand times smaller still. There would be no difficulty even in showing the attraction between two No. 5 shot.
And now, in conclusion, I would only say that if there is anything that is good in the experiments to which I have this evening directed your attention, experiments conducted largely with sticks, and string, and straw and sealing wax, I may perhaps be pardoned if I express my conviction that in these days we are too apt to depart from the simple ways of our fathers, and instead of following them, to fall down and worship the brazen image which the instrument maker hath set up.
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NATURE, COMPOSITION, AND TREATMENT OF ANIMAL AND VEGETABLE FABRICS.
The inseparable duties of studying the composition of the various animal and vegetable fabrics, as also their nature—when in contact with the various mineral, vegetable, animal, and gaseous bodies applied in the individual industries—should not devolve upon the heads, chemists, or managers of firms alone. It is most important that every intelligent workman, whom we cannot expect to acquire a very extensive knowledge of chemistry and perfect acquaintance of the particular nature and component parts of fabrics, should, at least, be able to thwart the possibility of the majority of accidents brought about in regard to the quality and aspect of materials treated by them.
In the treatment of wool the first operations are of no mean importance, and the whole subsequent operations and final results, almost as a whole, depend on the manner in which the fleece washing had been effected. In presence of suintine, as also fatty matters, as well as the countless kinds of acids deposited on the wool through exudation from the body, etc., the various agents and materials cannot act and deposit as evenly as might be desired, and the complete obliteration of the former, therefore, becomes an absolute necessity.
For vegetable fabrics a great technical and practical knowledge is already requisite in their cultivation itself, and before any operations are necessary at all. One of the greatest points is the ripeness of the fibers. It is almost an impossibility to produce delicate colors on vegetable fabrics which were gathered inopportunely. Numerous experiments have been made on cotton containing smaller or larger quantities of unripe fibers, and after the necessary preceding operations, have been dyed in rose, purple, and blue colors, and the beauty of the shades invariably differed in proportion to the greater or lesser quantities of unripe fibers contained in the samples, and by a careless admixture of unripe and unseasoned fibers the most brilliant colors have been completely spoiled in the presence of the former. These deficiencies of unripe vegetable fibers are so serious that the utmost precautions should be taken, not only by planters to gather the fibers in a ripe state, but the natural aspect of ripe and unripe fibers and their respective differences should be known to the operators of the individual branches in the cotton industry themselves.
The newest vegetable fabrics, as ma (China grass), pina, abaca, or Manila hemp, agave, jute, and that obtained from the palm tree, must be tended with equal care to that of cotton. The ma, or China grass, is obtained from the Boehmeria nivea, as also from the less known Boehmeria puya. The fibers of this stalk, after preparing and bleaching, have the whiteness of snow and the brilliancy of silk. By a special process—the description of which we must for the present leave in abeyance—the China grass can be transformed into a material greatly resembling the finest quality of wool. The greatest advantage afforded in the application of China grass is, moreover, that the tissues produced with this fiber are much more easily washed than silks, and in this operation they lose none of their beauty or their quality.
The abaca is produced from the fibrous parts of the bark of the wild banana tree, found in the Philippines. Its botanical denomination is Musa troglodytarum. The abaca fiber is not spun or wrung, but is jointed end to end. The threads are wound and subsequently beaten for softening, and finally bleached by plunging in lime water for twenty-four hours, and dried in the sun.