354 



NATURAL THEOLOGY. 



forcing-pumps are carried into the reservoir, and 

 they fill it half full of water, c ; the mouth of the 



pipe, D, which is to convey away the water, reaches 

 into the water in the reservoir. As the w^ater rises, 

 the air is compressed : so that, although the pumps 

 act alternately, the elasticity of the contained air 

 acts uninterruptedly in pressing on the surfare of 

 the water, and raising it by the tube, d, in an 

 equable stream. The elasticity of the contained 

 air fills up the interval between the actions of the 

 pumps, and admits of no interruption to the force 

 with which the water is propelled upwards. 



Surely these are sufficient indications of the ne- 

 cessity of three powers acting in propelling the 

 blood from the heart. The first is a sudden and 



