538 Mr. H. Wilde on the Velocity 



By a calculation similar to that for the higher pressures, 

 we obtain for the initial velocity with which the atmosphere 

 rushes into a vacuum through a hole in a thin plate 



V= -r-p- x — — — =633 per second, 



633 — 

 or V = -wrr =1021 feet per second for the contracted vein. 



That the differences between the theoretic and experimental 

 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 1 lb. of pressure were found to be in the ratio of 

 4 to 1 , 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 experiments show 

 that 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 different densities was discharged into the atmosphere, 

 induced me to repeat the experiments with the same apparatus 



Table III. — Discharge into the Atmosphere. 

 Barometer 30*17. Thermometer 59° F. 



Effective pres- 



Time of 



Apparent 



Velocity- 



sure, in pounds 



discharge, 



velocity, 



coefHcient 



per square inch. 



in seconds. 



per second. 



•62. 



15 



8-0 



1266 



2043 



14 



8-25 



1318 



2126 



13 



8-5 



1373 



2214 



12 



9-0 



1413 



2280 



11 



95 



1454 



2345 



10 



100 



1519 



2450 



9 



10-5 



1609 



2595 



8 



11-5 



1652 



, 2664 



7 



125 



1734 



2797 



6 



135 



1876 



3026 



5 



155 



1985 



3202 



4 



175 



2110 



3403 



3 



220 



2300 



3710 



2 



290 



2616 



4219 • 



