146 MR. H. WILDE ON THE VELOCITY 



X. On the Velocity with which Air rushes into a Vacuum, 

 and on some Phenomena attending the Discharge of 

 Atmospheres of Higher into Atmospheres of Lower 

 Density. By Henry Wilde, Esq. 



Eead October 20th, 1885. 



Considering the present condition of our knowledge 

 respecting the mechanical properties of air and other 

 gaseSj some apology might appear to be needed in bringing 

 before this Society the results of an investigation touching 

 some fundamental principles in pneumatics which for 

 more than a century have been considered to rest on 

 foundations as secure as the laws of gravitation of the 

 heavenly bodies. A survey of the history of the dynamics 

 of elastic fluids will, however, show that, great as are the 

 advances which have been made in this branch of science, 

 the laws of the discharge of elastic fluids under the varied 

 conditions of elasticity and volume are still left in much 

 obscurity. The several circumstances which have combined 

 to produce this anomalous state of our knowledge of this 

 subject are : — (i) The application of the laws of discharge 

 of inelastic fluids, without any modification, to those which 

 are elastic; (2) the confusion of the quantity of the 

 discharge of elastic fluids after leaving the vessel, with the 

 velocity of discharge through the aperture in the vessel ; 

 and (3) the want of a sufficient number of experiments, 

 under varied conditions and through sufficient range of 

 pressure, to compare with the deductions derived from 

 theory. 



It has hitherto been assumed, as a leading proposition 

 in pneumatics, that air rushes into a vacuum with the 



