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



Table III. 

 Discharge into a Vacuum 1*5 inch Mercury 



Lb. per 



square inch 



absolute 



Hole in 

 thin plate. 



Plain tube- 

 orifice. 



Conoidal 

 orifice 

 inside. 



Conoidal 

 orifice 

 outside. 



Coefficient 



for 



orifice. 



pressure. 







A 



D 



D 



O 



15 



16-0 



15-0 



16-0 



16-0 



•937 



14 



17-5 



16-5 



18-0 



18-0 



•943 



13 



19-0 



17-5 



20-0 



200 



•921 



12 



21-0 



19-5 



22-5 



220 



•928 



11 



23-0 



21-5 



24-5 



24-0 



•935 



10 



25-5 



24-0 



27-5 



27-0 



•941 



9 



28'5 



27 



31-0 



30-5 



•947 



8 



32-5 



31-0 



35-5 



350 



•954 



7 



37-5 



35-5 



41-0 



40-0 



•947 



6 



45-0 



42-5 



49-5 



48-5 



•944 



5 



550 



52-5 



630 



61-5 



•955 



4 



70-0 



67-0 



81-0 



79-0 



mean 



3 



102-0 



101-0 



125-0 



120-0 



coeffi- 

 cient 



2 



180-0 



192-0 



241-0 



2240 



•941 



A comparison of the times of discharge through D with the 

 conoidal orifice in both positions will show that they approach 

 nearly to a ratio of equality. The phenomenal change in the 

 rate of discharge from the same orifice was consequently due 

 to the diminished resistance of the external atmosphere, the 

 conoidal form of the orifice increasing the amount of rare- 

 faction above that obtained with a plain tube-orifice. This 

 conclusion is further evident on comparing the times of 

 discharge from D in reversed position ;from a pressure of 

 3 lb. to 1 lb. ; for as the rarefaction in the vacuum-chamber 

 was only reduced to 1*5 inch of mercury, the phenomenal 

 change in the rate of discharge again presents itself, making 

 a difference of 17 seconds in the times of discharge between 

 the reversed position of the orifice for the lowest pressure. 



Comparing the times of discharge through the tube-orifice 

 A and the orifice O in the thin plate, it will be seen that 

 there is much less difference between them than for 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 discharge through 



