388 
PROFESSOR GRAHAM ON THE MOTION OF GASES. 
1 cubic inch of air into a vacuum in 22 seconds, the time of passage of a constant 
volume of air into a vacuum was 853 seconds at 60°, 899 seconds at 1 16°, and 924'5 
seconds at 152°. The theoretical times, or those corresponding to the rarefaction by 
heat at these temperatures, are 853,945 and 1004 seconds. Here the observed times 
at 1 16° and 152°, are 46 and 79’5 seconds shorter respectively than the times obtained 
by calculation ; and the difference in transpirability observed at the high and low 
temperatures only amounts to about one-half of what it should be. 
With capillary M, of which the resistance is seven times greater than the last 
capillary, the observed times of air at 59° (15° centig.), and at 203° (95° centig.), were 
1106‘5 and 1286‘4 seconds. The time at the higher temperature is 1400 seconds 
by calculation, and the observed time is therefore 113*6 seconds deficient. The dif- 
ference at the high and low temperatures amounts to nearly two-thirds of the differ- 
ence which theory requires. The deviation is therefore less than with the preceding 
capillary. 
Air compressed in the globular digester with pressure gauge, of which the capacity 
was reduced to about 10 cubic inches by the introduction of mercury, was transpired 
by a small capillary V, 3 inches in length, into the atmosphere, from a pressure be- 
ginning at 17 inches above that of the barometer. Thermometer 50°, barometer 
29*546 to 29*590. 
The resistance of this capillary is excessive. Under a pressure of 17 inches of 
mercury, 1 cubic inch of air is transpired in 2329 seconds, or the volume transpired 
is 0*0258 cubic inch per minute. 
Table XV. — Transpiration of air under pressure (into air) at different temperatures. 
Pressure by gauge barometer. 
Time in seconds. 
Ratio at 203°, 
Time at 50° = i. 
Thermometer 50° Fahr. 
Thermometer 203° Fahr. 
17 inches. 
0 
« 
0 
16 
1370 
2329 
1-7000 
15 
1445 
2442 
1-6900 
14 
1541 
2601 
1-6880 
From 17 to 14 inches 
4356 
7372 
1-6924 1 
Now the volume of air at 3*2° being =1, at 50° it is 1*0366, and at 203°, 1*3480. 
But it must be remembered that the volume actually transpired in the experiment 
was greater at 203° than that at 50®, in proportion as the volume of air is expanded at 
the higher of these two temperatures, that is as 1*3480 to 1*0366 (volume at 32°= 1). 
It is therefore necessary to reduce the observed times of the table at 203° in that pro- 
portion. The time from 17 inches to 16 is thus reduced from 2329 to 1792*5 seconds, 
which last is the true time of the passage of the same volume at 203° as passed at 
50°. The law requires that the times of equal volumes should be inversely as the 
densities of air at these temperatures, or as 1*0366 to 1*3480. Thus calculated from 
