PROFESSOR GRAHAM ON THE MOTION OF GASES. 
387 
hydrogen at 203°, 0-4357 and 0-4392, numbers which might have been obtained at 
atmospheric temperatures. 
Carbonic acid, however, appears to present a sensible deviation from this uni- 
formity of rate. In a series of observations made upon this gas at 60°, 203°, 299° 
and 347°, its transpiration time referred to air at the same temperatures was 0-8291, 
0-8551, 0-8/77 and 0-8907 ; and referred to oxygen, 0-7448, 0-7541, 0-7741 and 0-7855. 
The transpiration time of carbonic acid at 347° varied in other experiments from 
|)-7729 to 0 - 7905 , the time of oxygen being 1. The protoxide of nitrogen gave the 
pumber 0-7969 at the same high temperature. 
The time of oxygen appears also to become relatively slower at high tempei-atures, 
Although much less considerably than carbonic acid. It gave the numbers 0-8877 
and 0-8860 for air at 347°, instead of 0-8984, the number at low temperatures. As 
we may assume from its uniform relation to hydrogen that the nitrogen remains 
constant, it follows that the oxygen has become relatively slower in transpiration at 
the high temperature. 
If oxygen deviates from a supposed normal rate at high temperatures, it cannot 
necessarily coincide with that rate at any lower temperature, which is accidental, 
such as that of the atmosphere. But this influence of heat upon the transpiration 
time of oxygen is, I believe, still sensible at the low temperature in question. 
By increasing the time of oxygen, this influence of heat may be the cause of that 
slight deviation, so uniform in its amount, of the observed times of air and nitrogen 
from their theoretical times, which was always remarked. I am disposed then to 
look upon the slight inconstancy of transpiration rate observed in some gases at dif- 
ferent temperatures, as a fact of the same class as the deviations from their theoretical 
specific gravities observed in a greater or less degree in the same substances, and to 
those other points in which all the gaseous bodies we have to operate upon depart in 
some measure from the mechanical idea of a perfect gas. 
The normal effect of temperature upon transpiration, as observed in air, varies I 
find with the resistance of the capillary in a much higher degree than any other pro- 
perty of transpiration ; the retardation from the same change of temperature being 
much greater in a capillary of great than small resistance. The resistance of a capil- 
lary such as M, which exhibits so exactly the law of densities, is insufficient to bring 
out the full effeet of temperature. With the fine tubes of the compound capil- 
lary, on the other hand, the limit to the retarding influence of heat seems to be 
reached. The retardation then appears to be simply in proportion to the expansion; 
and rarefaction by heat, therefore, to have the same effect upon transpiration as ex 
pansion from diminished pressure. 
In illustration of this inequality of action upon heated air, I may refer to results 
obtained by two capillary tubes of small and of intermediate resistance, before stating 
the normal results of capillaries of extreme resistance. 
With the copper capillary tube described in my former paper, and which admitted 
