224 ON DIVERGING STREAMS 



shewed itself also between the valve and a 

 part of its seat. When it was raised half an 

 inch, the same point, //, which in Fig. 3, shews- 

 the greatest vacuum, indicated a pressure of a 

 quarter of an inch of mercury, while the circle 

 of greatest vacuum, had removed farther from 

 the aperture. 



It has been suggested, that the formation of 

 the vacuum may be accounted for from the 

 known tendency of a compressed spring, when 

 liberated, to fly beyond the point at which it 

 will finally settle. But this action of a spring 

 is only one instance of the operation of a general 

 law of nature which is applicable to all bodies. 

 When any body elastic or non-elastic is put in 

 motion, its inertia causes it to continue in motion 

 in the direction in which it has been impelled 

 until its force is expended. The force of a 

 liberated metallic spring is expended in the 

 effort to overcome the tenacity of the substance 

 of which it is composed, while the force of a 

 cannon ball, fired into an earthen bank, is 

 expended on the resistance presented by the 

 earth ; but it is projectile force that is expended 

 in both instances. 



ADDENDA. 



In a short time after the phenomenon of the 



