OF HYDRAULIC ENG1 131 



depression, the valve a will rise to let the bucket go LECT. 

 down ; and when it is quite down, the valve a will fall v^-^^v. 

 by its weight, and stop the hole in the bucket. When 

 the bucket is next raised, all the water above it will be 

 lifted up, and begin to run off by the pipe F. And thus, 

 by raising and depressing the bucket alternately, there 

 is still more water raised by it ; which, getting above 

 the pipe F, into the wide top /, will supply the pipe, 

 and make it run with a continued stream. 



So, at every time the bucket is raised, the valve b, 

 rises, and the valve a falls ; and at every lime the bucket 

 is depressed, the valve b falls, and a rises. 



As it is the pressure of the air or atmosphere which 

 causes the water to rise, and follow the piston or bucket 

 G as it is drawn up ; and since a column of water 33 

 feet high is of equal weight with as thick a column of 

 the atmosphere, from the earth to the very top of the 

 air ; therefore, the perpendicular height of the piston 

 or bucket from the surface of the water in the well 

 must always be less than 33 feet ; otherwise the water 

 will never get above the bucket. But, when the height 

 is less, the pressure of the atmosphere will be greater 

 than the weight of the water in the pump, and will 

 therefore raise it above the bucket : and when the water 

 has once got above the bucket, it may be lifted thereby 

 to any height, if the rod D be made long enough, and a 

 sufficient degree of strength be employed, to raise it 

 with the weight of the water above the bucket. 



The force required to work a pump will be as the 

 height to which the water is raised, and as the square 

 of the diameter of the pump-bore, in that part where 

 the piston works. So that, if two pumps be of equal 

 heights, and one of them be twice as wide in the bore 

 as the other, the widest will raise four times as much 

 water as the narrowest : and will therefore require four 

 times as much strength to work it. 



The wideness or narrowness of the pump, in any 

 K 2 



