199 



exceed in durability and ease of 

 working those formerly con- 

 structed of wood, and excel all 

 others in cheapness. Fig. 168 

 exhibits the working of the com- 

 mon pump, the water first pass- 

 ing through the fixed valve be- 

 low, and then through the one 

 in the piston ; both opening up- 

 ward, it can not flow back with- 

 out mstantly shutting them. 

 The water is driven up by the 

 pressure of the atmosphere, ex- 

 plained m the next chapter. 



The most perfect pump, per- 

 haps, in present use, 

 is the best-construct- 

 ed Chain Pump, a 

 cross-section of one 

 of which is here 

 shown {Fig. 169). 

 The chain is made 



Fig. 



Common Pump : b, loiccr or fixed 

 valve, G, piston with valve, a, 

 opening upward ; D d, piston- 

 rod ; F, spout. 



to revolve rapidly on the angular wheel by 

 means of a winch attached to the upper one, 

 and being furnished with a regular succes- 

 sion of metallic discs which nearly fit the 

 bore in the tube, a, the water is carried up 

 in large quantities. Wlien the motion is 

 discontinued, the water settles down again 

 into the well, and consequently this pump is 

 not Hable to accident by freezing. By 

 sweeping rapidly through the water, it pre- 



