ivith which Air rushes into a Vacuum, 



537 



of calculation the velocities for the discharge of each 5 lb. of 

 pressure from 135 lb. to 10 lb. have been found. 



The velocity with which air rushes into the vacuum, as seen 

 from the table, is considerably less than that which has hitherto 

 been assigned to it by theory, and is not constant for all 

 pressures, as might have been expected from the known ratio 

 of elasticity and density : the difference in the velocities be- 

 tween each discharge for the higher pressures, as will be seen, 

 is so small as to be exceeded by experimental errors. The 

 amount of this difference will, however, appear more clearly 

 when we are considering the velocity of air discharged into 

 the atmosphere. Meanwhile I may remark that the velocities 

 increase with the pressures by small asymptotic quantities, so 

 that the theoretic velocity of 1332 feet per second would be 

 obtained at a pressure of 40 atmospheres if the law of Boyle 

 and Mariotte held good for so high a density. 



While the rate of each discharge may be considered ap- 

 proximately uniform for the higher pressures, the initial and 

 terminal velocities of each discharge of 5 lb. for the lower 

 pressures would be much different. This is specially notice- 

 able for the velocity (842 feet per second) assigned to atmo- 

 spheric pressure of 15 lb. ; and as it was a matter of much 

 interest that this important constant of nature should be de- 

 termined with all the accuracy attainable, experiments were 

 made to ascertain the velocity of discharge for every pound of 

 pressure from 15 lb. to 2 lb. In these experiments the read- 

 ings were taken from the mercurial gauge, and the vacuum 

 in the chamber was reduced to 0*4 of an inch of mercury. 



The results obtained are shown in the table. 



Table II. — Discharge into a Vacuum 0*4 inch Mercury. 

 Barometer 29*96. Thermometer 60° F. 



Absolute pres- 



Time of 



Velocity, in 

 feet per second. 



Y el o city- 



sure, in pounds 

 per square inch. 



discharge, 

 in seconds. 



coefficient 

 •62. 



15 



16-0 



633 



1021 



14 



17-5 



621 



1001 



13 



190 



614 



990 



12 



210 



606 



977 



11 



23-0 



600 



968 



10 



25-5 



596 



961 



9 



28-5 



593 



956 



8 



32-5 



584 



942 



7 



37-5 



577 



931 



6 



45-0 



563 



908 



5 



55-0 



559 



901 



4 



70-0 



542 



874 



' 3 



1020 



497 



802 



2 



180-0 



421 



679 



