Chapter 3

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 ¾ in. for a model of 10 ft. long to 1¼ in. and 1½ 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 Illustré_ 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 £400,000 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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QUARTZ FIBERS.[1]

[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.