218 



MACHINERY rS" CONNECTION WITH WATER. 



placed ill an inclined position, with one end in water, and 

 made to revolve, the water resting at the lower side of 

 each turn of the screw is gradually carried from one end 

 to the other, and discharged at the upper extremity. Its 

 simplicity and small liability to get out of order render 

 the Archimedean screw sometimes useful where water is 

 to be raised from an open stream to a short distance, as 

 for irrigation, the motion being easily imparted to it by 

 means of a small water-wheel, driven by the stream. 



PUMPS. 



Great improvement has been made in tTie common 

 Tig. ^42. pump for farms within a few years. 



The best cast-iron pumps, made 

 almost wholly of this metal, ex- 

 ceed in durability and ease of 

 working those formerly con- 

 structed of wood, and excel others 

 in cheapness. Fig. 242 exhibits 

 the working of the common pump, 

 the water first passing through 

 the fixed valve below, and then 

 through the one in the piston ; 

 both opening upward, it cannot 

 flow back without instantly shut- 

 ting them. The water is driven 

 up by the pressure of the at- 

 mosphere, explained in the next 

 chapter. 



Fig. 243 is an iron cistern pump, 

 showing the mode of bolting it to 

 the floor or platform, and rep- 

 resenting, also, its neat and com- 

 pact form, occupying but little 



Common Pump : b, lower or fixed t ^i 



valve, G, piston with valve, a, spacc at ouc Side, or m the comcr 



opening upward; H d, piston- / i -, ^ 1^ . 



rod; F, spout, of a kitchen, over the cistern. 



