with ivhich Air rushes into a Vacuum. 539 



and under precisely the same conditions as those which had 

 been made into a vacuum as above described. The results 

 are shown in Tables III. and IV. 



On comparing the times of discharge in Table III. and the 

 velocities calculated therefrom with the times and velocities 

 in Table II., a remarkable difference will be observed in them 

 for the same effective pressures. Thus, the velocity of dis- 

 charge from 15 lb. to 14 lb. appears to be double that 

 assigned to the same pressure when the discharge is made 

 into a vacuum ; while in the discharge from 2 lb. to 1 lb. 

 (the lowest pressure in the table) the velocity appears to be 

 more than six times greater, or 4219 feet per second. No 

 less remarkable than this apparent increase in the rate of dis- 

 charge is the complete inversion of the order of the velocities 

 as compared with those when the discharge was made into a 

 vacuum for the same effective pressure. Now, we have 

 knowledge of several causes competent to diminish the velo- 

 city of air of constant temperature flowing into the atmosphere, 

 but none to increase the velocity except the form of the 

 aperture, which in this case remained unchanged. Recog- 

 nizing the fact that when air of 15 lb. effective pressure was 

 discharged into the atmosphere the cylinder actually con- 

 tained two atmospheres of absolute pressure, we are led to the 

 conclusion that the phenomenal increase in the rate of dis- 

 charge observed is caused by the external atmosphere acting 

 as a vacuum, and offers no resistance to the discharge into it 

 of air of 15 lb. pressure, which thereby becomes 30 lb. effec- 

 tive pressure. The velocity of air of 15 lb. effective pressure 

 discharged into the atmosphere based on this conclusion is 

 1021 feet per second, the same as the velocity found for the 

 discharge into a vacuum. For effective pressures below 

 15 lb. the velocities are compounded of the rate of discharge 

 into a vacuum, and the resistance of the atmosphere without 

 any regular ratio, but approximating to the square roots of 

 the pressures. 



That the atmosphere acts as a vacuum to the discharge of 

 air into it of 15 lb. effective pressure, is further evident from 

 the results obtained, and shown in Table IV. 



