316 Cooper’s Rotative Pistor 
can be thrown with simple power. But with this advantage 
there is a disadvantage, in as much as the stream being ope- 
rated upon directly by the power, gives, in its motion, an ex- 
act representation of the mode of its application; conse- 
quently the stream is as unequal as the force applied, and, at 
every change of the piston, stops. To remedy this defect, 
a vessel filled with air is placed in the vicinity of the piston 
cylinder, and the water, ere its fina! discharge, is forced into 
he f this vessel and then allowed to escape. As 
the pipe, through which the water makes its final escape, 1s 
generally much smaller than the piston cylinder, consequert- 
ly the motion of the piston will produce compression on the 
water at every stroke, while the air, in the air chamber, be- 
comes compressed in like manner. The advantage, then, 
of the air chamber is, that this compressed air operates upon 
the water as a spring, and exerts its power during the suspen- 
