The following are the dimensions of the three cylinders given by Desaguliers : Outer Cylinder. Middle Cylinder. Inner Cylinder.
Length, 30 inches. 29.0 inches 31.2 inches.
Inner diameter, 6.74 6 35 6.03 Thickness, 0.10 0.08 0.13 Outer diameter, 6.94 6.51 6.29 The quantity of mercury used is 362 pounds, which rises up to the height of 16 inches between the inner and outer cylinder.
With regard to the effect of this engine, Dr. Desagu liers informs us, that a man raised a hogshead of water 18 feet high in a minute, but he could not continue this exer tion above ith of an hour. When he wrought, however, so that he could continue six or eight hours a-day, he. raised a hogshead between 10 and 11 feet in a minute, which De saguliers considers as the maximum effect produced by a man with the best water engine. Dr. Robison likewise admits that there can be no doubt of the performance of this engine excelling that of any other pump which raises the water to the same height. He considers it as peculiarly applicable in nice experiments for illustrating the theory of hydraulics, as it would give the finest pistons for mea suring the pressures of water in pipes.
8. Description of Dr. Robison's Improvement on Gosset and De la Deuille's Pump without Friction.
Dr. Robison describes this improved pump as without friction—as capable of being constructed in a variety of forms by any common carpenter, and as of great utility in raising a large quantity of water to a small height, or in draining marshes and marle pits, quarries, &c.
In Plate CCCCLXX, Fig. 12, ABCD is a square trunk, formed of four planks of wood, open at both ends, and having at its upper end a spout B, and a little cistern AB. Near its lower end is a wooden partition, perforated with a hole, in which is a clack valve E. To this wooden parti tion is nailed a long cylindrical bag, ffff, having its upper end fixed to a round board, perforated with a hole containing a valve F. This bag may be made of leather, or of double canvass, a fold of thin leather, or of sheep's skin, being placed between the too folds. The upper end of the bag should be firmly tied with a cord, in a groove turned out of the rim of the board at F. Into the board
at F is fixed the fork of the piston rod FG, and the bag is kept distended by a number of wooden hoops or rings of strong wire ff,ff, and fixed to it at a few inches distance from one another, and kept at the same distance by three or four cords, binding them together, and stretching from the top to the bottom of the bag. The distance of the hoops should be nearly twice the breadth of the rim of the wooden ring to which the upper valve F, and piston rod FG, are attached, '‘ Now let this trunk," says Dr. Robison," be immersed in the water. It is evident that if the bag be stretched from the compressed form which its own weight will give it, by drawing up the piston rod, its capacity will be enlarged, the valve F will be shut by its own weight, the air in the bag will be rarefied, and the atmosphere will press the water into the bag. When the rod is thrust down again, the water will come out at the valve F, and fill part of the trunk. A repetition of the operation will have a similar effect ; the trunk will be filled, and the water will at last be discharged by the spout.
"Here is a pump without friction, and perfectly tight ; for the leather between the folds of canvass renders the bag impervious both to air and water. We know from experiment, that a bag of 6 inches diameter, made of sail cloth No. 3, with a sheepskin between, will bear a column of 15 feet of water, and stand 6 hours work per day for a month, without failure, and that the pump is considerably superior in effect to a common pump of the same dimen sions. We must only observe, that the length of the bag must be three times the intended length of the stroke; so that, when the piston rod is in its highest position, the angles or ridgus of the bag may be pretty acute. If the bag be more stretched than this, the force which must be exerted by the labourer becomes much greater than the weight of the column of water which he is raising. If the pump be laid aslope in these occasional and hasty drawings, it is necessary to make a guide for the piston rod within the trunk, that the bag may play up and down with out rubbing on the sides, which would quickly wear it out.