The very singular and simple hydraulic motor which we illustrate herewith is the invention of a Russian engineer, Mr. Jagn. It is scarcely as yet known in Western Europe, where, however, something will probably be heard of it ere long. Its true field would seem to be Egypt, India, or any country where canals or rivers are used for irrigation, and where it is desired to draw water from them at particular spots in the simplest and cheapest manner. At present in nearly all such cases water is raised by hand or steam power; nevertheless it must be obvious that the current of the canal itself, slow though it may be, is quite sufficient to raise a small portion of the discharge to the very moderate height generally needed to lift it over the banks into the adjoining fields. Why then is it not employed for the purpose? The answer is obvious, when we consider the various hydraulic motors at present in use. Of course, motors worked by water pressure must here be excluded; and we are left with scarcely anything but the undershot wheel, the turbine, and the screw pump.

All these require expensive buildings and erections to set them to work, present but a very small fraction of their surface to the water at any one time, and must be very large and costly if they are to draw even a very moderate amount of power from such a source. There is no possibility of adjusting them readily to suit variations in the speed of the current or in the quantity of water required, nor of moving them from place to place should this be convenient.

PARACHUTE HYDRAULIC MOTOR.

The motor of Mr. Jagn is on a totally different principle. Its essential features consist, as shown, of an endless rope made of hemp or aloe fiber, which takes a turn or two round a pair of drums mounted on a barge or pontoon, and then passes down the channel to return over a pulley hung from a floating punt, at such a depth that the whole of the rope is immersed in the water. Along this rope are suspended at equal intervals a number of parachutes made of sail cloth. The rope passes through the center of each of these, and to it are attached a series of strings, the other ends of which are connected to the outside edge of the parachute. Thus they act like the spokes of an umbrella to prevent the parachute from opening too far under the pressure of the current. The parachutes must be placed so far apart that the current may act fairly on each, and the sum of the pressures forms the force which draws the rope through the water. The moment, however, that any parachute has passed round the return pulley, the current acts upon it in the opposite direction. It then shuts up like an umbrella, and assumes a volume so small that its resistance on the return journey is insignificant.

After passing round the drum at the upper end, it at once opens afresh of its own accord, and once more becomes part of the moving power of the whole system. The parachutes are formed by first cutting out a complete circle of cloth, and then taking from this a sector equal to one-fifth or one-sixth of the total area. Such parachutes are found to keep their form when stretched by the water better than a surface originally spherical, although the latter would be theoretically more correct. The motion of the drum is transmitted by spur, gear, or otherwise as may be required, to give the requisite speed.

It will be seen that the advantages of the system are as follows: First, the facility it offers for obtaining a large working area, which may be increased or diminished at will, according to the requirements of the moment, by lengthening or shortening the rope. Secondly, the ease with which it is erected and set to work. Thirdly, the small part of the river section which it occupies, so as to present no obstacle to navigation. Fourthly, the ease with which it can be mounted on a barge of any kind, and carried wherever it may be needed. Fifthly, it is not stopped, like all other hydraulic motors, by the appearance of ice - it has, in fact, already been worked under ice in the Neva. At the same time, winds and waves have no influence upon it.

The principle of the apparatus is not altogether new. In 1872 there was tried on the Ohio River an arrangement termed the Brooks motor. It was composed of two drums, placed horizontally and parallel to each other. Round these there passed endless chains at equal spaces apart on the length of the drums, and to these chains were fixed wooden blades or arms of a curved form, and so jointed to the frames that they opened when moving in one direction, and closed down on the chain when moving in the other. In this machine the weight of the chains was a serious obstacle to obtaining any large amount of power. The whole apparatus was mounted on a heavy wooden scaffold, which proved an impediment to the flow of the river. Again, the resistance due to the surface of the returning blades and to their stiffness was found to be far from insignificant.

In the present system Mr. Jagn has found, after many experiments, that the best effect was obtained when the parachutes were spaced apart at twice their diameter, and when the rope made an angle of 8 degrees to 10 degrees with the current. It is found that when open and in motion the parachutes never touch the bottom. This was the case with a rope containing 180 parachutes of 4 feet diameter, and working in a depth of only 6 feet. This is easily explained by the fact that the velocity of a current always diminishes as it approaches the bottom. Hence the pressure on the lower part of the parachute will be less than that on the upper part; but the former pressure tends to draw the parachute downward, while the latter tends to raise it to the top of the water. Thus, the latter being the larger, the parachute will always have a tendency to rise. In fact, it is necessary to sink the return pulley sufficiently deep to make sure that the parachutes will not emerge from the surface. For the same reason no intermediate supports are needed over the driving span; if any are needed it is for the return span, on which the parachutes are closed.

Of course, if metal were used instead of hemp, the case would be entirely different, and intermediate supports would have to be used for anything but very moderate lengths.

In practice, Mr. Jagn has employed two ropes wound upon the same pair of drums, which are mounted upon a pontoon. The ropes are spread out from each other, as in Fig. 1, making an angle of about 10 degrees. The low specific gravity of the system enables ropes to be employed of as great a length as 450 yards, each of them carrying 350 parachutes of 17.2 square feet area. As half of these are in action at the same time, the total working area for the two cables is 5,860 square feet. This immense area furnishes a considerable amount of power even in a river of feeble current. Comparing this with a floating water wheel of the type sometimes employed, and supposing this to have only 172 square feet of working area, such a wheel must have a length of 46 feet, a diameter of 23 feet, and seventy-two floats, each 2½ feet wide. The enormous dimensions thus required for a comparatively small working area point sufficiently clearly to the advantage which remains on the side of the parachute motor.

The general arrangement of the system is shown in the engraving. Behind the return pulleys, D D, are attached cords, A A, with some parachutes strung upon them. These present their openings to the current and preserve the tension of the connecting ropes. At the further end of each cord is a board, B, which is kept in a vertical plane, but lying at a slight angle to the direction of the current; and this acts to keep the two moving ropes apart from each other. The two return pulleys are, however, connected by a line, E, which can be shortened or lengthened from the pontoon, and in this way the angle of inclination between the two ropes can be varied if required. A grooved pulley presses upon the trailing span at the moment before it reaches the circumference of the drum. It is mounted on a screwed spindle, which is depressed by a nut, and thus makes the wet rope grip the outside of the drum in a thoroughly efficacious manner.

The author has made a theoretical investigation of the power which may be developed by the system, and has worked out tables by which, when the velocity of the current and the other elements of the problem are known, the power developed by any given number of parachutes can be at once determined. We do not reproduce this investigation, which takes account of the resistance of the returning parachutes and other circumstances, but will content ourselves with quoting the final equation, which is as follows: T = 0.328 S V³. Here T is the work done in H.P., S is the total working area in sq. m., and V is the velocity of the current in m. per sec. Taking V = 1, and S = 1 sq. m., which is by no means an impracticable quantity, we have T = 0.328 H.P. per sq. m. We may check this result by the equation given, in English measures, by Rankine - "Applied Mechanics," p. 398 - for the pressure of a current upon a solid body immersed in it. This equation, F = 1.8 m A v² / 2g, where m is the weight of a unit of volume of the fluid - say 62 lb. - A is the area exposed, and v the relative velocity of the current. Mr. Jagn finds that the maximum of efficiency is obtained when the rope moves at one-third the velocity of the stream.

If this velocity be 3 feet per second, we shall have v = 2. and we then get F = 7 lb. per sq. ft. very nearly. Now 1 sq. meter = 10.76 sq. ft., and a speed of 1 ft. per second (which is that of the rope) is 60 ft. per minute. Hence the H.P. realized in the same case as that taken above will be 7 × 10.76 × 60 / 33,000 = 0.137 H.P. The difference between the two values is very large, but Rankine, of course, depends entirely on the value of the constant 1.8, which is quite empirical, and is for a flat band instead of a hollow parachute. Taking, however, his smaller figure, and an area of 544 square inches, which Mr. Jagn has actually employed, we get a gross power of = 0.137 × 544 = 7.43 H.P. Hence it will be seen that the amount of power which can be realized by the system is far from being inconsiderable.

Lastly, we may point out that the durability of the apparatus will be considerable. There is no wear except at the moment when the rope is passing round the drum, and even then there need be no slipping or grinding. The apparatus worked in the Neva was in very good condition after running for four months day and night. After five months about one-fifth of the parachutes had to be replaced, but after seven months the hemp rope still showed no signs of wear. We think we have said enough to show that for certain purposes, and especially, as we have, already mentioned, for irrigation purposes, the new motor is well worthy of a careful and extended trial. It may be questioned even whether we have not here the germ of an idea which may hereafter enable us to solve one of the most interesting and important of engineering problems, viz., the utilization of the great store of power provided for us twice daily in the ebb and flow of the tide. - The Engineer.