158 MR. H. WILDE ON THE VELOCITY 



resistance of the atmosphere without any regular ratio^ but 

 approximating to the square roots of the pressures. 



That the atmosphere acts as a vacuum to the discharge 

 of air into it of 15 lb. eflFective pressure^ is further evident 

 from the results obtained, and shown in Table IV. 



In this Table it will be observed that the times of each 

 discharge from 120 lb. to 15 lb. effective pressure into the 

 atmosphere are identical with the times of discharge from 

 135 lb. to 30 lb. absolute pressure into a vacuum. Hence 

 we are able to formulate and prove the general proposition 

 that the atmosphere acts as a vacuum, and offers no resist- 

 ance to the discharge of air of all pressures above two 

 absolute atmospheres. 



Although the times of discharge for each reduction of 

 5 lb. of pressure_, as we have seen, are the same as those 

 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 pressure 

 would be useful as exhibiting some further points of 

 interest, and revealing the fallacy involved in estimating the 

 velocities from the eflFective pressures. On comparing the 

 velocities of each discharge from 120 lb. to 40 lb., 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 diflference of the 

 theoretic and experimental velocities with which air rushes 

 into a vacuum by the same method of calculation. This 

 diflference, as will be seen, amounts to exactly one atmos- 

 phere of pressure. 



For each reduction of 5 lb. from 120 lb. to 40 lb. 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 



