WITH WHICH AIR RUSHES INTO A VACUUM. 153 



the discharging orifice and the vena contracta by applying 

 the hydraulic coefficient "62. 



From this Table it will be seen that the time of discharge 

 of 5 lb. from 135 lb. absolute pressure is 7*5 seconds. 

 Now, as 5 lb. pressure is the ~ part of the total pressure, 



we have ^^"^ = 21-22 cubic inches of air from 135 lb. 

 27 "^ 



pressure discharged into the vacuum chamber in 7*5 



seconds : 01% in another form, since 5 lb. and 191 cubic 



inches of air ab atmospheric pressure are equivalents, so 



191 cubic inches condensed at 9 atmospheres — =21*22 



cubic inches of discharge, as in the above calculation. 

 Again, we have for a cubic inch extended into a cylinder 

 0"02 of an inch in diameter (the size of the dis- 

 charging orifice), 265-25 feet x 21-22 = 5628 feet. Hence 



V=^ ?- = 7'io feet per second for the discharge of 



7-5 seconds 1 -^ ^ 



air from 135 lb. to 130 lb. into a vacuum through a hole in a 



750 

 thin plate. Or V = ^^=i2io feet per second when the 



orifice is formed to the contracted vein. By the like 

 method of calculation the velocities for the discharge of 

 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 between 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 



