496 Mr. H. Wilde on the Efflux of Air as 



An examination of this table will show that the form of 

 the orifice has very little influence on the rate of discharge 

 of elastic fluids compared with what it has on those which 

 are inelastic. 



No difference was observable in these experiments in the 

 rates of discharge through the orifices A, B, and C; notwith- 

 standing that A was a plain cylinder, and B and C were 

 coned to a depth of half their thickness and formed tubes 

 from three to six diameters in length. Moreover, although 

 the results shown in the tables were obtained with the coned 

 sides of the orifices inside the vessel, yet, when the sides 

 were reversed, the rate of discharge through A, B, and C was 

 only diminished by one thirtieth part, and there was no dif- 

 ference in the rate of discharge through D whether the coned 

 side of the orifice was inside or outside the vessel. 



Taking A, B, and C as the orifices producing the maximum 

 rate of discharge, we have '935 as the value of the coefficient 

 of discharge from an orifice in a thin plate for the highest 

 pressure of 135 lb. This value, as will be seen, is the same 

 for all the pressures in the table within errors of observation 

 and experiment, and the mean value of the coefficient for all 

 the pressures is '937. 



Applying this coefficient to the velocity deduced in Table I. 



of my former paper for an orifice in a thin plate, we have for 



the maximum velocity with which air of 135 lb. pressure 



750 

 rushes into a vacuum, before expansion, Y=^^ = 800 feet 



per second. 



Some anomalous rates of efflux from the same orifice, which 

 were obtained when air of less than 15 lb. effective pressure 

 was discharged into the atmosphere, induced me to make a 

 series of experiments on the discharge of air of an initial 

 pressure of 15 lb. through the same orifices as in the last 

 experiments, and the times were recorded for each reduction 

 of 2 lb. of pressure. 



All the discharges were made with the conoidal orifices 

 inside the vessel, but they were also made through C and D 

 with these orifices outside the vessel. The results are shown 

 in the following table (II. ). 



On comparing the times of discharge through the several 

 orifices among themselves, and with those in Table I., a 

 marked difference is observable in them. Thus the ratio of 

 discharge through the tube-orifice A and the orifice in a thin 

 plate is greater than that for the same orifices in Table I., 



