29 
for pressures one atmosphere higher, when the discharge 
was made into a vacuum, yet it seemed to me that a table 
showing the apparent velocities due to the effective pres- 
sures would be useful as exhibiting some further points of 
interest, and revealing the fallacy involved in estimating 
the velocities from the effective pressures. On comparing 
the velocities of each discharge from 120 lbs. to 40 lbs. it 
will be seen that the theoretic velocity of 1332 feet per 
second is as nearly attained as the units of pressure and 
time adopted in these experiments would permit. We have 
therefore in the table a measure of the difference of the 
theoretic and experimental velocities with which air rushes 
into a vacuum by the same method of calculation. This 
difference, as will be seen, amounts to exactly one atmo- 
sphere of pressure. 
For each reduction of 5 lbs. from 120 lbs. to 40 lbs., the 
times of discharge are inversely as the pressures ; and as 
the density of the issuing stream of air diminishes in the 
same proportion, the velocity of discharge is the same for 
all the pressures from 120 lbs. to 40 lbs., as shown in the 
table. Hence it appeared to me at the commencement of 
this investigation that the theoretic and experimental velo- 
cities with which air rushes into a vacuum were rigorously 
exact. The anomalous and apparent increase in the veloci- 
ties from 40 lbs. to 10 lbs., however, led me to suspect that 
the atmosphere in some manner affected the results, and 
induced me to make the discharge into a vacuum with the 
results shown in Table I. 
That the phenomenal rate of discharge which I have 
described should not hitherto have manifested itself in some 
form, or be associated with some facts explanatory of it, 
would indeed be surprising considering the varied circum- 
stances in which the discharge of elastic fluids comes into 
play. Hence, it has long been known that a jet of air 
issuing from an aperture in a vessel produces a rarefaction 
