390 
PROFESSOR GRAHAM ON THE MOTION OF GASES. 
culated. In one experiment which was made upon oxygen at 49° and 203°, the in- 
crease upon the time at the higher temperature corresponded within 0‘7 per cent, of 
the increase upon the time of air, and evidently followed the same ratio. I may add 
that the transpiration times of air and oxygen, as determined by a single observation 
in each case, were 0"9058 to 1 for the compound capillary Q, and 0'9020 to 1 for the 
single capillary V of extreme resistance. 
In conclusion I may sum up the general results hitherto obtained in this 
inquiry. 
1. The velocities with which different gases pass through capillary tubes bear a 
constant relation to each other, and appear to constitute a peculiar and fundamental 
property of the gaseous form of matter, which I have termed transpirability. The 
constancy of these relations, or of the transpiration times, has been observed for 
several of the gases for tube resistances varying in amount from 1 to 1000. These 
relations, there is reason to believe, are more simple in their expression than the 
densities of the gases. The following relations are particularly remarkable. 
The velocity of hydrogen is exactly double that of nitrogen and carbonic oxide. 
The velocities of nitrogen and oxygen are inversely as the specific gravities of these 
gases. 
The velocity of binoxide of nitrogen is the same as that of nitrogen and carbonic 
oxide. 
The velocities of carbonic acid and protoxide of nitrogen are equal, and directly 
proportional to their specific gravities, when compared with oxygen. 
The velocity of protocarburetted hydrogen is 0-8, that of hydrogen being 1. 
The velocity of chlorine appears to be that of oxygen ; of bromine vapour and 
sulphuric acid vapour the same as that of oxygen. 
Ether vapour appears to have the same velocity as hydrogen gas. 
Olefiant gas, ammonia and cyanogen to have equal or nearly equal velocities, which 
approach closely to double the velocity of oxygen. 
Hydrosulphuric acid gas and bisulphide of carbon vapour appear to have equal 
or nearly equal velocities. 
The compounds of methyl appear to have a less velocity than the corresponding 
compounds of ethyl, but to be connected by a certain constant relation. 
2. The resistance of a capillary tube of uniform bore to the passage of any gas is 
directly proportional to the length of the tube. 
3. The velocity of passage of equal volumes of air of the same temperature but of 
different densities or elasticities, is directly proportional to the density. 
4. Rarefaction by heat has a similar and precisely equal effect in diminishing 
the velocity of the transpiration of equal volumes of air, as the loss of density and 
elasticity by diminished pressure has. 
5. A greater resistance in the capillary is required to bring out the third result, or 
the law of densities, than appears necessary for the first and second results ; and a 
