24 
From this Table it will be seen that the time of discharge 
of 51bs. from 1351bs. absolute pressure is 7‘5 seconds. Now, 
as 51bs. pressure is the 2 V part of the total pressure, we 
573 
have = 21*22 cubic inches of air from 1351bs. pressure 
discharged into the vacuum chamber in 7’5 seconds : or in 
another form, since 51bs. and 191 cubic inches of air at 
atmospheric pressure are equivalents, so 191 cubic inches 
condensed to 9 atmospheres 
m 
9 
= 21*22 cubic inches of dis- 
charge 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 discharging orifice) 265*25 feet 
X 21-22 = 5628 feet. Hence Y = f ^ - =750 feet per 
7.5 seconds 
second for the discharge of air from 1351bs. to 1301bs. into 
750 
a vacuum through a hole in a thin plate. Or Y = = 
1210 feet per second when the orifice is formed to the con- 
tracted vein. By the like method of calculation the veloci- 
ties for the discharge of each 51bs. of pressure from 1351bs. 
to lOlbs. 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 con- 
stant 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 pres- 
sures, as will be seen, is so small as to be exceeded by ex- 
perimental errors. The amount of this difierence 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 
approximately uniform for the higher pressures, the initial 
and terminal velocities of each discharge of 5 lbs. for the 
