OF COMPRESSED AIR. 221 



When the circular valve b, in Fig. 1, is 

 placed on the seat, there is stagnant atmospheric 

 air v;rithin the aperture b. On the condensed 

 air being admitted into the pipe a, the stagnant 

 air is put into motion, and before it can overcome 

 the inertia of the valve, is forced between the 

 outer parts of the valve and its seat. The air, 

 while being thus forced is, however, compelled 

 to diverge from a circle, whose diameter is 2|ths 

 to one of a larger diameter, and is consequently 

 dilated and attenuated. The impulse given by 

 the compressed air on its first admission, to 

 the stagnant air in the pipe, causes the stagnant 

 air to commence the process, but the compressed 

 air follows instantaneously, and through the 

 force with which it is impelled by the original 

 moving power, is projected under the valve, and 

 there forced to diverge with a velocity propor- 

 tioned to the amount of the projectile force. 



The projectile force acting through the stream 

 of compressed air, and the peculiarly shaped 

 and confined space through which the air is 

 driven, are then the causes of its dilatation, until 

 its degree of rarity is beyond that of the 

 atmosphere, when atmospheric pressure on the 

 upper side of the valve preponderates. 



This view will, perhaps, be illustrated, by sup- 



