WITH WHICH AIR RUSHES INTO A VACUUM. 155 



By a calculation similar to that for the higher pressures, 

 we obtain for the initial velocity with which the atmos- 

 phere rushes into a vacuum through a hole in a thin plate 



V = ^-^ X — ^-r-^ = 677 feet per second, 

 15 16 -^-^ ^ 



or 



V= ~^= 102 1 feet per second for the contracted vein. 

 •62 ^ 



That the differences between the theoretic and experi- 

 mental velocities was not caused by the friction of the 

 stream of air against the circumference of a smaller orifice 

 being greater in proportion to that of the circumference 

 of a larger orifice, was proved by discharging air of 15 lb. 

 pressure through a hole one hundredth of an inch in 

 diameter in another similar thin plate, when the times of 

 discharge through the short range of i lb. of pressure 

 were found to be in the ratio of 4 to i, or inversely 

 as the areas of the orifices. 



Taking into further account the difference between the 

 initial and terminal velocities due to the reduction of 

 pressure from 15 lb. to 14 lb., the results of these experi- 

 ments show that with an absolute pressure of 30 inches of 

 mercury, and at a temperature of 60° Fahrenheit, the 

 atmosphere rushes into a vacuum with a velocity not 

 greater than 1050 feet per second, or less than the velocity 

 of sound. 



Some anomalous rates of discharge which I obtained 

 when air of difierent densities was discharged into the 

 atmosphere, induced me to repeat the experiments with 

 the same apparatus and under precisely the same con- 

 ditions as those which had been made into a vacuum as 



