148 MR. H. WILDE ON THE VELOCITY 



through the same tube at equally low pressures in 8' 15" 

 and 8' 11" respectively. Again, while the velocities of 

 discharge of inelastic fluids are as the square roots of the 

 heads, some mathematicians have justly considered that 

 this law does not apply to those which are elastic, and 

 have assumed with good reason (though what appears 

 unlikely at first sight) that the velocity of air discharged 

 into a vacuum is the same for all pressures. But whatever 

 differences of opinion there may be amongst natural 

 philosophers on this point, all are agreed in estimating the 

 quantity of air discharged from a higher into air of a 

 lower density, from the difference between the two 

 densities, as in the similar case of the discharge of inelastic 

 fluids, by the difference or effective head producing the 

 pressure. This mode of determining the amount of the 

 discharge from a higher to a lower density, like that of the 

 velocity of the atmosphere into a vacuum, has not, so far 

 as I know, been made the subject of experiment through 

 any considerable range of pressure. It therefore appeared 

 to n:e that, as each gas has its specific velocity of discharge, 

 such a series of experiments might be useful in confirming 

 and extending our knowledge of the dynamics of elastic 

 fluids. In the course of these experiments I have met 

 with some results which I thought of sufficient importance 

 to bring before the Society. 



The apparatus employed in this investigation consisted 

 of two strong cylinders of cast iron, shown in the 

 engraving. The small cylinder. A, had an internal 

 capacity of 573 cubic inches, while the large cylinder, B, 

 had a capacity of 8459 cubic inches, or about fifteen times 

 the capacity of the cylinder A. To the top of this cylinder 

 was fitted a syringe for condensing the air up to nine 

 atmospheres, and also a Bourdon^s pressure-gauge of an 

 improved construction, graduated through every pound of 



