modified by the Form of the Discharging Orifice, 499 



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 dis- 

 charge of atmospheres of higher into atmospheres of lower 

 density, the times and coefficients in Table 1. and Table III. 

 for the higher pressure may well be considered as having been 

 obtained for discharges into a perfect vacuum, the difference 

 in the coefficients for pressures below 10 lb. in Table III. 

 being entirely due to friction of the issuing stream of air 

 against the sides of the orifices. 



From the results shown in Tables I. and II. the maximum 

 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 co- 

 efficients which have hitherto been applied to the efflux of air 

 below 15 lb. effective pressure derive nearly the whole of 

 their value from the phenomenal changes of resistance 

 between the discharging and receiving atmospheres, and not 

 from the forms of the orifice and length of the adjutages, as 

 in the discharge of inelastic fluids. 



Applying the coefficient -937 to the velocity with which the 

 atmosphere of 15 lb. absolute pressure rushes into a vacuum 

 before expansion, as deduced in table ii. in my former 



paper, we have V = 7007 = 677 feet per second, or ap- 

 proximately one half the velocity due to the height of the 

 homogeneous atmosphere. 



The following approximate velocities with which atmo- 

 spheres of several gases of 15 lb. absolute pressure rush into a 

 vacuum through an orifice of the best form, before expansion, 

 have been calculated on the basis of Graham's law of the 

 velocities of efflux for equal pressures being inversely as the 

 square roots of the specific gravities. 



Air .... . 1-000x677= 677 feet per second. 



Oxygen . . . .0-950x677= 643 „ „ 



Nitrogen. . . . 1-015x677= 687 „ ., 



Hydrogen . . . 3*800x677 = 2572 „ '„ 



Saturated steam . 1-445x677= 978 „ 



