PROFESSOR THOMAS GRAHAM's SCIENTIFIC WORK. 197 



fouiul to be disproportionately retarded to a greater extent even tliau 

 tlieir effusion rates by the admixture with theui of heavier gases. Fur- 

 ther, by employing mixtures of gas and vapor, Mr. Graham extended 

 his inquiry so as to include a determination of the transpiration times 

 of several vapors; the results being calculated on the assumption 

 that the observed transpiration time of the mixture was the mean of 

 the transpiration times of the permanent gas and of the coercible vapor 

 experimented on. In this way the transpiration time of ether vapor, 

 sp. gr. 2.0SG, was shown to be identical with that of hydrogen gas, sp. 

 gr. 0.0C9 ; and the transpiration time of carbonic sulphide vajior, sp. gr. 

 2.645, identical with that of sulphureted hydrogen gas, sp. gr. 1.191. 



With respect to gas transpiration in general, the rates of transpira- 

 tion of different gases were found to be independent of the nature of 

 the material of the capillary ; apjiarently from the capillary, of what 

 material soever,, becoming lined with a film of gas, with which alone the 

 current of gas conld come in contact ; so that the friction was purely 

 intestine, and suggestive of a sort of viscosity in the gas itself. The 

 rate of passage was further shown to be iuversel3" as the length of the 

 capillary ; and directly, in some high but nndetermined ratio, as its di- 

 ameter. Lastly, the rate of "effusion" of a given volume of any par- 

 ticular gas being independent of pressure and temperature, the rate of 

 transpiration of a given volume of any particular gas was observed to 

 vary directly with its variation of density, whether the result of altera- 

 tion of pressure or of temperature ; 100 cubic inches of dense air, for 

 example, transpiring more rapidly than 100 cubic inches of tenuous air, 

 in proportion to the excess of density. 



Speaking of the importance and fundamental nature of the physical 

 l^roperties manifested by bodies in the gaseous state, and of the extent 

 of his own inquiries on gas-transpiration, Mr. Graham observed : " It 

 was under this impression that I devoted an amount of time and atten- 

 tion to that class of constants (transpiration-velocities) which might 

 otherwise appear disproportionate to their value and the importance 

 of the subject. As the results, too, wei»e entirely nov^el, and wholly un- 

 provided for in the received view of the gaseous constitution, of which 

 indeed they prove the incompleteness, it was the more necessary to 

 verify each fact with the greatest care." 



* VII. 



iJlJfmUm of ga.ws. — In 1801, Dalton, in an essay " On the constitu- 

 tion of mixed gases, and particularly of the atmosphere," propounded 

 the now celebrated view that " where two elastic fluids denoted by A 

 and B are mixed together, there is no mutual repulsion among their par- 

 ticles ; that is, the. particles of A do not repel those of B, as they do one 

 another; consequently the pressure or whole weight upon any one par- 

 ticle arises solely from those of its own kind." During the act of ad- 

 mixture, ''the particles of A meeting with no repulsion from those of 



