188 EFFLUX OF AIR MODIFIED BY THE DISCHARGING ORIFICE. 



the same orifices in Table II., the ratio agreeing very 

 closely with those shown in Table I. for similar times of 

 discharge. The approaching equality in the times of dis- 

 charge through the tube orifice A and the orifice in the 

 thin plate for the lower pressures is, no doubt, due to the 

 friction of the issuing stream of air against the sides of 

 the tube orifice. The effect of this friction for the lowest 

 pressure, as will be seen, reduces the rate of discharge 

 from the orifice A below that from the orifice in the thin 

 plate. 



From the results of my previous experiments on the 

 discharge of atmospheres of higher into atmospheres of 

 lower density, the times and coefficients in Table I. and 

 Table III. for the higher pressures may well be considered 

 as having been obtained for discharges into a perfect 

 vacuum, the difference in the coefficients for pressures 

 below 10 lbs. in Table III, being entirely due to fric- 

 tion of the issuing stream of air against the sides of the 

 orifices. 



From the results shown in Tables I. and II. the maxi- 

 mum rate of efflux is obtained from the orifices A, B, and 

 C, and taking the efflux from these orifices as unity, the 

 value of the coefficient for the efflux of air into a vacuum 

 through an orifice in a thin plate is '937. 



These experiments also prove conclusively that the 

 coefficients which have hitherto been applied to the efflux 

 of air below 15 lbs. effective pressure derive nearly the 

 whole of their value from the phenomenal changes of 

 resistance between the discharging and receiving atmo- 

 spheres, and not from the forms of the orifices and lengths 

 of the adjutages, as in the discharge of inelastic fluids. 



Applying the coefficient "937 to the velocity with which 

 the atmosphere of 15 lbs. absolute pressure rushes into a 

 vacuum, before expansion, as deduced in Table II. in my 



