On the Principles of Pump-lVork, S99 



the piston moves faster than the water can rise to follow 

 iu Hence we see the great use of contracting; the pipe 

 AD and making the piston play in a large head EKLT, a$ 

 bv this means we lessen the velocity of the piston and in- 

 crease that of the rising water, which can never be in any 

 danger of being wire-drawn. 



77. Since in the case of a piston's working in a pipe 

 ABCD, the diflerence between 34 feet and the length of 

 the pipe is always equal to half the length of the pipe, for 

 the force to be applied to the greatest advantage; therefore 

 22-6 feet is the greatest height of such a pump, because in 

 this case the velocity of the piston by the maximum force, 

 and that of the water in the pipe by the air's pressure, are 

 equal, viz. to 38 feet per second. 



78. But when the maximum force is applied to the lever, 

 the motion of the piston is thereby rendered so slow that 

 there will always be a velocity of the water, from the pres- 

 sure of air, greater than that of the piston at a less height 

 than 30 feet. For admitting the pipe 30 feet high, and the 

 air in its lightest state equal to a pressure of 32 feet of 

 water, then the difference of two feet will generate an uni- 

 form velocity of water of more than 1 1 feet per second, 

 which is many times more than that of the piston. 



79. Hence it follows, that if two pistons be employed, 

 they will not only have water enough, and to spare, but 

 also keep that water in a constant uniform motion by their 

 alternate action ; but to answer this end, the water must 

 rise in but one pipe, and be communicated at the top, by 

 two separate valves, to pistons working in two different 

 barrels placed in one common cistern EFGH. 



80. To such a pump likewise a double lever MM may 

 be applied to the wheel K, so that the pistons maybe moved 

 in a perpendicular direction on each side: at the two ends of 

 this lever the men may stand in the best manner to work 

 the pump ; six, eight, or ten, as occasion requires. And 

 thus we have at last arrived to the idea of a sucking-pump, 

 which, as far as I am able to judge, will have all the ad- 

 vantages that 5uch a machine is any ways capable of. 



LIV. Ni^ticf 



