a Norwegian (Steinitz, p. 41); and the birds sent forth by Noah are thus recalled to notice.

The foregoing paper was further illustrated by an original sketch of a Nile boat made by a Mahommedan, which strikingly resembled the "Heaven-bound ship" depicted by Clemens as a symbol of the "Christian church." Also by an old sketch from the Roman catacombs, in which Noah's ark is shown as a chest with a man in it, and a lock and key. Also by a modern drawing of a steam-boat by a Chinese painter, which contrasted with a sketch of the 'Great Eastern' steam-ship.

On a new Railway Signal. By Dr. GRAY.

The author said the new railway-signal had been tested very satisfactorily upon the Midland Great Western Railway. The qualities which it possessed, and which were relied on as establishing its value and efficiency, were,-First, the signal could be made from the guard to the driver and back again with certainty and rapidity. Secondly, that the guard and driver should be able to communicate with each other by means of a code of signals. Thirdly, that in certain cases the signal apparatus should be selfacting automatic; for instance, if any accident caused the severance of the train, which would prevent any communication between the guard and the driver by the voluntary action of either, that notice of the fact would be conveyed to them by the apparatus itself. Fourthly, that there should be no special skill required in order to manage or make the signal; what he meant by that was, that it should not be liable to derangement, and that in case some derangement did occur, the ordinary workmen employed on railway works would be able to set the apparatus right or make a new one. Fifthly, that there should be always a constant indication before the parties in charge of the train that the signal was in working order, so that the guard would not start from the station without knowing that the signal was all right and in reliable condition, and would not fail him upon the journey. The sixth requisite was, that the communication between the carriages should be of such a nature that there would be no serious delay in making up the train of carriages, because of the use of the signal.

The author entered at some length into the principles and details of the invention, and exhibited a working model, the size of the actual apparatus, and several experiments were then tried, all of which worked successfully.

The essential principle of the signal was stated to be the producing, in a metal tube of about inch bore, and which was placed along the entire train of carriages, a more or less perfect exhaust, and causing the distribution of that exhaust to act on the signals. A common exhaust-pump, worked by an excentric on the axle of the guard's van, works the pump when the train moves, and instantly exhausts the air from the tube. This action causes a piston-head that plays in a little cylinder at the end of the long tube which is placed in front of the driver, to be pressed up into the cylinder by the external air, and to carry with it and out of view, a red bar or semaphore. This bar remains invisible when all is right, but the guard, by turning a cock on his end of the tube like a gas-cock, destroys the exhaust and lets down the red bar or danger signal in front of the driver's eye. The semaphore is so adjusted, that it is in fact also a weighted lever on a little steam cock to which a whistle is fitted, and when it is let down to indicate danger, it turns on steam by its falling, and so attracts the driver's attention by the whistle. The tube from carriage to carriage has a flexible pendent and a telescope air-tight connexion. This allows freedom of motion, and on the severance of a train the tube is opened, and all the signals given at both ends of the train. Similar signals, the steam whistle alone excepted, are placed in the guard's van, and the driver or any passenger can communicate with him by opening a stopcock. A little treddle placed near the guard's foot enables him to test the apparatus, and ascertain if the connexions are all right before the train moves. The excentric then maintains the exhaust.

The signals were made through a tube 168 feet in length with the greatest rapidity, and the air was exhausted at one end by an air-pump, but by a simple turning of the cock the effect of this exhaustion was destroyed, and a red bar or semaphore was thrown across a little box representing the box beside the driver, and a whistle was also made to sound by the same instrumentality.

On the Construction of the 36-inch Mortars made by order of Her Majesty's Government. By R. MALLET.

He

The author gave a verbal account of the two 36-inch wrought-iron mortars, and of the 36-inch shells constructed from his designs for the British Government. described the peculiarities of their construction, to avoid difficulties of manufacture and of transport in service; and contrasted the powers of demolition as against fortified places, of these large shells, or transferable mines, with the 13-inch shell, the largest heretofore in use, concluding with some remarks on the application of wrought iron to artillery.

On Tangent-Wheels. By GUILDFORD L. MOLESWORTH.

The author first presented some general views in hydraulics, and compared the efficiency of water-wheels, turbines and tangent-wheels. He then described and showed diagrams of a small wheel somewhat similar to the tangent-wheel, for a small workshop.

A description was then given of a tangent-wheel sent by the author to Tasmania for driving a corn-mill of six pairs of stones, with the dressing machinery. The fall was 270 feet, with an available quantity of 24 cubic feet of water per second. The water was confined in a pipe and brought down to act on the periphery of a wheel 3 feet in diameter, which revolved at a velocity of 360 revolutions per minute; the rims of the wheel were turned up truly on the shaft, and the edges of the inlet carefully faced to correspond with them; the buckets were of wrought iron, cast into the rims, curved and ventilated; the conditions to be observed in forming the curve of the buckets were described as requiring the water to enter without shock, remaining in the bucket sufficiently long to expend its vis viva, and then leaving it without diminishing the effect; the formation of these curves being the most important feature in producing an efficient machine.

The toe of the shaft was so arranged as not to be submerged, and the oiling was managed by a convenient apparatus.

The mechanical effect of the tangent-wheel was stated to be from seventy-five to eighty per cent., which was rather higher than that of Fourneyron's turbine.

Some experimenters had affirmed that Fourneyron's turbines had given out as much as eighty-five or ninety per cent., but it was evident that such statements must arise from some mistake; the consumption of power from different causes was stated to be about twenty-five per cent., leaving only seventy-five per cent. available; the probable source of error was supposed to have arisen from the use of incorrect coefficients for efflux in gauging the amount of water passing through the turbine and probably in some instances from neglecting the element of velocity in the body of water gauged. Castel's formula of Q=3·5 LH √H+035 va was given as applicable to the case.

It was also stated, that in practice Whitelaw's turbines gave much less mechanical effect than that usually attributed to them, viz. seventy-five per cent. The causes of loss of power were enumerated, and it was said that many which had been erected on the Continent had given great dissatisfaction, and had been for the most part replaced either by water-wheels, tangent-wheels, or turbines of a different kind. The tangentwheel had, on the contrary, replaced well-constructed over-shot wheels, and had been highly approved of.

The advantages of the tangent-wheel were summed up as follows:-1st. The water deviated less from its course and was less broken up than in turbines. 2ndly. The tangent-wheel was capable of such regulation as to work with varying quantities of water with undiminished effect, one quarter of the maximum quantity of water producing as good a proportional effect as the maximum. 3rdly. It was cheap and simple, and required no expensive foundations. 4thly. The toe of the shaft was not submerged in the tail-water. 5thly. The working parts were easily got at, and the wheel taken out in a few minutes for examination or repair. 6thly. The velocity of the wheel was not dependent on the quantity of water. 7thly. The motion was extremely steady and regular.

The method of placing the wheel with its axis horizontal was stated to have been tried, but without success, owing to the difficulty of freeing it of water.

In conclusion, it was urged that the tangent-wheel was applicable to many falls in which the adoption of the water-wheel was not only unsuitable but impracticable; and that much water-power which was at present wasted, might be utilized by means of it. It was applicable to all kinds of work, and might be used for agricultural purposes with great advantage.

On the Want of Facts respecting the Performance of Vessels at Sea.

By Admiral MOORSOM.

The author had himself arrived at results both in speed and in power for a great variety of types which appeared very near the truth; and if a similar method of investigation were applied to carry out experiments conducted at sea under a vast variety of conditions as to form, size, and circumstances, rules might be established which would serve to determine much of what was now the subject of controversy, and go far to remove the reproach on the greatest maritime nation of the world, which was contained in the following passage of a work by Mr. Scott Russell :-" It is admitted that out of every three steam-vessels that are built, two fell very far short of fulfilling the intention with which they were constructed."

Improvements in the mode of Working Steam-Engines. By T. Moy.

By drawings the author showed how he proposed to work steam-engines. No. 1 was an elevation plan and cross section of a pipe-boiler. The boiler is composed of a continuous tube, which may be arranged as in the drawing or in any other efficient mode, and is always kept full of water. By the circulation of the water, the cylinder is always kept at the same heat as the boiler. The heated water circulates through the boiler, jacket, and valve-box of the cylinder; the upper and hottest end of the tube communicates with the upper part of the jacket, and the lower end of the tube carries the cooled water back to the boiler. An open communication is maintained in any convenient place or places between the jacket and valve-box. The slide-valve (Drawing No. 2) has three cavities in it. The upper and lower cavities are for receiving and delivering the necessary quantity of water from the valve-box to the steam-passage. The middle cavity is for the eduction. Before the water-cavity of the valve arrives with its supply of water at the steam-port, its communication with the valve-box is cut off, and this portion of water turns into steam and works the piston. In the drawing No. 2, the upper water-cavity is shown as having arrived opposite the upper passage and the piston has just commenced the down-stroke, while the used steam under the piston is passing off through the eduction. The throttle-valve and regulator must be on the eduction.

The author mentions a plan for controlling the number of inches of water supplied to the cylinder at each stroke without stopping the engine. The engine always works expansively.

Suppose an engine, the internal capacity of whose cylinder is equal to 3 cubic feet, to be supplied by the valve with 3 cubic inches of water at 500° Fahr. As soon as this is at liberty to enter the cylinder it begins to turn into steam, which will drive the piston until all the water has turned into steam; from this point of the stroke to the end the steam will work expansively, and at the end of the stroke will be just equal to the pressure of the atmosphere. By its then passing through the eduction into a surface condenser (without injection, and without attempting to obtain a vacuum), it can be condensed to water and returned to the boiler.

Suppose this engine to be used in a factory. If it is required to reduce the power of the engine in consequence of some of the work being thrown out of gear, this may be done in two ways-by reducing the temperature of the boiler, or by reducing the quantity of water supplied by the water-cavity of the slide-valve; in the former case the engine will work less expansively and with less pressure; in the latter more expansively and with the same pressure at the first portion of the stroke.

By this mode of working steam-engines, great safety with increased pressure and compactness may be obtained; incrustation of the boiler and priming of the cylinder will be prevented.

On the Philosophy of the Wave-Line System of Ship-building. By T. Moy. The purport of this paper was to explain the mode of forming the wave-line; the rea son why the wave-line is the best form for vessels; and to show how speeds equal to fifty miles an hour and upwards may be attained by using the wave form in its integrity. The mode of forming the wave-line was shown in the drawing exhibited. Treating water as subject to the same laws as solid bodies in motion, it was urged that the best motion for one atom of the column of water in travelling its 20 feet from the cutwater to the extent of the midship section, is that which the piston of a steamengine would receive if connected with a crank of the length of 10 feet, the connecting rod being supposed to be infinite. The wave-curve imparts this motion to each atom, and therefore to the whole column of water; and any attempt to make this line either fuller or sharper will cause a decrease of speed. Also that any angle whatever formed at the stem with the line of motion is improper and highly detrimental to speed. It was proposed that the common term "resistance" is inapplicable, and that the term "duty" is preferable.

The subject was then illustrated by supposing a vessel of 40 feet beam, 100 feet length of bow, and 200 horse power to travel at ten miles an hour; this vessel's duty would be that of giving motion to two columns of water, one on each side of her keel at right angles to her course, at a speed of 176 feet per minute or 2 miles an hour. This vessel was called No. 2. No. 3, with a bow 200 feet long, the same midship section, and 400 horse power, will perform the duty of putting the water in motion at 176 feet per minute or 2 miles an hour, while she performs 20 miles an hour. No. 4, with 250 feet bow and the same midship section and 500 horse power, will put the water in motion at the same speed, 176 feet per minute or 2 miles an hour, while the vessel performs 25 miles an hour; and No. 5, with a bow 500 feet long and the same midship section, performs the same duty of putting the water in motion at the same low speed of 2 miles an hour, while she travels at the speed of 50 miles an hour, and only requires 1000 horse power,-while the Great Eastern,' in consequence of her great beam, would have to give motion to the column of water equal to 63rd miles an hour, in order to attain a speed of 50 miles an hour. A vessel of 8000 tons and 1000 horse power could be built upon the above sharp lines to travel at the rate of 50 miles an hour.

The following is the rule to find the speed of the water at right angles to the line of motion:-Divide the speed in feet per minute by the length of bow and multiply the product by half the length of beam, which gives the speed of the column of water in feet per minute. The following Table was referred to:

On the Laying of Submarine Telegraph Cables. By Sir J. MURRAY.

Mr. B. A. MURRAY made some observations on the advantages of "spinning silk from the cocoon," and exhibited a model of machinery invented and patented by him for effecting the new process; and stated that silk spun in this manner was perfectly even and free from knots, and consequently greatly superior to the article produced by the old system; in addition to which a great saving of labour and machinery was effected; weft being produced in one operation, and organgine in two operations, from the cocoon. One speciality of the patent is the spinning of the skeining reel

and bobbin*.

* Applied to raw silk, the machine in one operation spins, doubles, and throws silk wound to a bobbin from the skein.

Some Facts on the Flow of Water through Circular Pipes.
By J. NEVILLE.

On the Submarine Electric Telegraph Cable. By A. BALESTRINI.

On the Principle of the Transformation of Structures.

By W. J. MACQUORN RANKINE, LL.D., F.R.S. L. and E. This paper consists of an explanation of some of the practical applications of a principle first communicated by the author to the Royal Society in 1856, viz.—if a structure of a given figure be stable under a system of forces represented by given lines, every structure whose figure is a parallel projection of the given figure is stable under a system of forces represented by the corresponding parallel projections of the given lines.

(Two figures are said to be parallel projections of each other when every pair of parallel and equal lines in one figure corresponds to a pair of parallel and equal lines in the other. Thus all circles and ellipses are parallel projections of each other; so also are all spheres and ellipsoids.)

This principle enables the design for a bridge with a sloping extrados and a distorted semi-elliptical arch to be deduced from the design for a bridge with a horizontal extrados and a semicircular arch. In like manner, from the figure of an equilibrated arch for sustaining the pressure of a fluid, which is equal horizontally and vertically, can be deduced the figure of an equilibrated arch for sustaining the pressure of earth, which is less horizontally than vertically in a given ratio; and various analogous problems can be solved with ease by the principle of the transformation of structures, whose solution by a direct process would be very tedious and difficult.

Continuation of Experiments to determine the Resistances of Screw-Propellers when revolving in Water at different Depths and Velocities. By GEORGE RENNIE, F.R.S., &c.

My former experiments exhibited some curious phenomena on the effects produced on the resistances of screw-propellers when revolving in water at high velocities and at different depths. The first idea of driving screw propellers at high velocities and immersed at different depths was stated to be due to Mr. Joseph Apsey, an engineer of Broad Wall, in the parish of Christ Church, Surrey, but from the experiments having been made in a close boiler, objections were made to them at Glasgow as being fallacious; and it was only after similar experiments had been made by me in the open water in the river Thames that they were confirmed. Those results were given in my last paper, published in the Transactions of the British Association' in 1856. Both series of experiments proved that the influence of velocity was much greater than that of depth, but that the joint action of velocity and depth was very remarkable. The present paper contains the results of experiments made on differently formed propellers, for the purpose of ascertaining, first, the effects of screw-propellers when confined in tubes of a conical form; secondly, the effects of form of propellers working alone and not in tubes.

The common two-bladed screw, 13 inches diameter, pitch 20 inches, 600 revolutions per minute, when working in a depth of 12 inches above top of screw, gave a pressure

ft. in.

17 in length.

The same two-bladed screw, when immersed and working in a depth of 12 inches above top of screw, gave a pressure of 144 lbs., or more than double of the pressure when confined by the tube.

Without working in a tube.-Effects produced by a three-bladed screw-propeller of similar diameter, 134 inches and pitch 20 inches, area of circle 1 square foot to the two-bladed screw and moved at the same velocity of 600 revolutions per minute, and immersion of 12 inches above the level of the screw without a tube,-157 lbs.