136 FERGUSON'S LECTURES. 



G, H, upon its axis, according to the strength of the 

 fall of water, and the height to which the water is intend- 

 e< ^ * ^ e ra i se d ky the engine, as the wheel turns 

 go by wa- round, these cranks move the levers c, d, e,f, g, h, up 

 and down, by the iron rods i, k, I, m, n, o ; which alter- 

 nately raise and depress the pistons by the other iron 

 rods p, q, r, s, t, u, w, x, y, in twelve pumps ; nine 

 whereof, as L, M, N, O, P, Q, R, S, T, appear in the 

 plate ; the other three being hid behind the work at V. 

 And as pipes may go from all these pumps, to convey 

 the water (drawn up by them to a small height) into 

 a close cistern, from which the main pipe goes off, 

 the water will be forced into this cistern by the descent 

 of the pistons. And as each pipe going from its res- 

 pective pump into the cistern, has a valve at its end in 

 the cistern, these valves will hinder the return of the 

 water by the pipes ; and therefore, when the cistern is 

 once full, each piston upon its descent will force the wa- 

 ter (conveyed into the cistern by a former stroke) up 

 the main pipe, to the height the engine was intended 

 to raise it which height depends upon the quantity rais- 

 ed, and the power that turns the wheel. When the 

 power upon the wheel is lessened by any defect of the 

 quantity of water turning it, a proportionable number 

 of the pumps may be laid aside, by disengaging their 

 rods from the vibrating levers. 



This figure is a representation of the engine erected 

 at Blenheim for the Duke of Marlborough, by the late in- 

 genious Mr. Aldersea. The water wheel is 71 feet in 

 diameter, according to Mr. Switzer's account in his Hy- 

 draulics. 



When such a machine is placed in a stream that runs 

 upon a small declivity, the motion of the levers and ac- 

 tion of the pumps will be but slow ; since the wheel 

 must go once round for each stroke of the pumps. But 

 when there is a large body of slow running water, a 

 C>g or spur wheel may be placed upon each side of the 



