PUMP. 



207 



Pump, without any play, so that the turned up edges of the 

 v -*-v~'~' leathern rings do not come up between the plunger 

 and the upper metal ring, but are lodged in a little 

 conical taper, which is given to the inner edge of the 

 upper plate, it* hole being wider below than above. 

 It is on this trifling circumstance that the great tight- 

 ness of the collar depends. To prevent the leathers 

 from shrinking by drought, there id usually a little 

 cistern formed round the head of the pump and kept 

 full of water."* 



The operation of this pump is almost exactly the 

 same as that of the forcing pump. When the bottom 

 b of the plunger is in contact with v, it nearly fills the 

 barrel. By drawing it up, a vacuum is made in the 

 barrel. The valve x is shut by the pressure of the at- 

 mosphere above, and the air below CD rushes through 

 the valve v into the barrel, and is followed by the wa- 

 ter, which rises in the suction pipe. The same opera- 

 tion being repeated, the water rises still higher in the 

 suction pipe, till it comes into the barrel. When the 

 plunger ab now descends in the barrel, it will drive the 

 water up into the main pipe through the valve x. 



This pump is said by Dr. Robison to have been in- 

 vented by Sir Samuel Moreland. The advantage con- 

 sists in the facility with which the plunger can be re- 

 paired, and the accuracy with which it may be made 

 to work. See Desaguliers' Experimental Philosophy, 

 vol. i. p. 166. 



6. Description of a Pump without Friction. 



Description This machine consists of a wooden tube ABCD, ei- 

 of a pump ther square or cylindrical, having a valve v at its lower 

 end. The depth of the water in the pit must be at 

 least equal to the distance of its surface NO from the 

 place of delivery K. A small cistern EADF is placed 

 at the top of the wooden tube, and on a level with K. 

 A tube KHG, with a valve at H, is united to the tube 

 at G. A beam of wood LM, and of at least the same 

 length as the tube, is suspended by a chain from a work- 

 ing beam, and is loaded with weights at L exceeding 

 the weight of the column of water displaced. If this 

 beam now descends by its own weight from the posi- 

 tion shown in the figure, the water between M and v 

 must rise all round it in the narrow space between it 

 and the tube ABCD, and when the bottom M comes to 

 v, the water will have risen to K, in the rising pipe 

 GHK. When the plunger LM is drawn up again to 

 the first position, as in the figure, the water in the tube 

 will sink again, but that in the rising pipe will remain 

 in consequence of the valve H having closed. When 

 the plunger descends a second time, the water will 

 again rise in the tube to K, and will now flow out at K, 

 and the quantity discharged will be equal to the part 

 of the plunger LM below the surface of the pit- water, 

 bating the small quantity between the plunger and the 

 tube, which may be made very small by a good work- 

 man. 



Dr. Robison observes, that he has seen a machine 

 consisting of two of these pumps, which was made 

 by an untaught labouring man, which had great power. 

 The plungers were suspended from the end of a long 

 beam, the upper surface of which was fixed into a 

 well with a hand-rail on each side. A man stood on 

 one end till one plunger descended to the bottom of its 

 tube, and he then walked quietly to the other end, the 

 declivity being at first about 25, but gradually grow- 



Dexrtip. 



lion of 

 HukhM 1 

 quiduihrer 

 pump with- 

 out friction. 

 PLATE 



CCCCLXX. 



Fig. 11. 



without 

 friction. 

 PLATE 



OCCCI.XX 



Fig. 10. 



ing less as he advanced. In this way he caused the 1'urap. 

 other plunger to descend, and so on alternately. Dr. > y 

 Robison informs us, that a very feeble old man, whose 

 weight was llo pounds, raised 7 cubic feet of water 

 1 1 4 feet high in a minute, and wrought eight or ten 

 hours every day. A stout young man, he adds, weigh- 

 ing nearly 135 pounds, raised 8j cubic feet to the same 

 weight in the same time, and when he was loaded 

 with 30 pounds, he raised <)\ to the same height, work- 

 ing ten hours a-day without fatigue. See Hobison's 

 Mechanical Philosophy, vol. ii. p. 671. 



7. Description of Haskins' Quicksilver Pump niihout 

 Friction. 



This very ingenious machine was invented by Mr- 

 Haskins and improved by Desaguliers, and has been 

 described in great detail in the Philosophical Transac- 

 tions for 1728, vol. xxxii. p. 5, and also in Dr. Desagu- 

 liers' Experimental Philosophy, vol. ii. p. 491. 



The first experiment which Mr. Haskins made was 

 with an engine which he erected at the house of Dr. 

 Desaguliers about 1720, but in that engine as much 

 mercury was moved every stroke as the water raised, 

 and consequently the expense of the mercury was very 

 great. Dr. Desaguliers however informed him that he 

 might accomplish his object with a very small quanti- 

 ty of mercury, and both Mr. Haskins and a Mr. Wil- 

 liam Vreem found out the construction represented in 

 Fig. 11. 



In this figure vmop is a cylindrical iron tube, about 

 six feet long, and open above. Another cylindrical tube, 

 ab, close at top, and of a smaller bore, is connected 

 with it at its bottom on. From the main pipe A pro- 

 ceeds a third iron cylinder efgh, which can move up 

 and down between the other two cylinders without 

 touching either of them. In the main pipe AB there 

 is a valve at v and another at x, as near as possible to 

 the pipe efgh. Let us suppose that the two con- 

 nected cylinders mnop and ab are suspended by chains 

 Cm, Cp, from the end of a working beam, and let mer- 

 cury be poured in between mnop and ab till it rises to 

 about three-fourths of the height inn. Let us suppose 

 also, that the lower end of the pipe AB is plunged in 

 the cistern of water, and that the valve v is not more 

 than 33 feet above the surface of the water. Let us 

 now suppose that the chains Cp, Cm, descend, and 

 along with them the cylinders ab, mnop, then the air 

 above a will be rarefied, the valve v will fall, and x will 

 rise, and a portion of water will rise in the suction 

 pipe B, and the pressure of the external air acting on 

 the mercury between the tubes efgh and mnop, will 

 make it descend in that space and rise in the space be- 

 tween efgh and the tube a b. As mercury is about 13 

 times heavier than water, it will rise 1 inch in that in- 

 terval for every 13 inches of rise in the water. If the 

 chains and their attached cylinders are now drawn up, 

 the air which formerly came from the pipe B will be pre- 

 vented from returning by the valve *. The valve v 

 will therefore rise, and the air will escape through it 

 at the pipe A. By a repetition of the operation, the 

 water will rise higher and higher in the suction pipe, 

 and the mercury rise higher and higher in the interval 

 between efgh and ab, till at last the water will Bow 

 through x and fill the whole apparatus. When this i* 

 done the cylinders have descended about 30 inches. If 

 they are now drawn up, the water in ef cannot return 



llobison'i Sytlcm of Mechanical Phiiotophy, roL ii. p. 665, 



