102 The Drainage of Fens and Low Lands, 



purposes on the Pacific coast, he obtained an efficiency of 

 from 65 to 70 per cent, for lifts up to 10 feet, and only 35 per 

 cent for lifts of 100 feet. 



The statical height of water which these pumps will support 

 without discharging requires a speed which varies in some 

 degree with the form of the blades. Mr. Thompson ^ states, 

 as the result of his experience, that the speed of the periphery 

 per second required to balance the weight of the water up to 

 the point of discharge is equal to eight times the square root 

 of the given height in small pumps, and 9*82 times in large 

 pumps. In a letter which appeared in * The Engineer ' of 

 September 24th, 1886, Mr. C. Brown gives, as the result of 

 experiments made by him with pumps having blades of the 

 form shown in Fig. 6, Plate 6 — the water being held at a 

 height of 45 feet — 



(i) Required a speed per second = s! 2gh, 



(2) ,, = considerably more. 



(3) „ still more. 



(4) >, 0'82 X JVgh, 



In a description of the pump made by Mr. C. Hett, of Brigg, 

 for the s.s. Eldorado, in 'The Engineer' of June i8th, 1886, it 

 is stated that Mr. Hett found a pump of his make with 2 feet 

 disc which gave a full discharge at a height of 16 feet 6 inches 

 when running 190 revolutions a minute, the velocity at the 

 periphery being only about two-thirds of the head due to 

 gravity. 



The following formula of Unwinds for ascertaining the speed 

 and discharge is given in Molesworth's ' Pocket Book ' : — 



S = 8 \^ H in small fans, or 9 • 5 V H in large fans, 



^ "^ 64 '' ^^ 90*25 '' " 



* 'Trans.' Inst. C.E., vol. xxxii. 



