PROPERTIES OF MATTER IN' THE GASEOUS STATE. 
843 
animal and vegetable world, and the work of destruction in the mineral world, are 
carried on within such spaces. The varying action of the sun must be to cause alter¬ 
nate inspiration and expiration of ah’, promoting continual change of air within the 
interstices of the soil as well as within the tissue of plants. What may be the effects 
of such changes we do not know, but the changes go on; and we may fairly assume 
that in the processes of nature the dimensional properties of gas play no unimportant 
part. 
Nor is this all. It is by aid of the analogy which gas affords us that we must look 
forward to solve the mystery of the luminiferous ether. And although all attempts to 
frame a satisfactory hypothesis as to the molecular constitution of ether have hitherto 
failed, in none of these hypotheses have the tangential and normal stresses arising 
from a varying condition been taken into account; whereas the recognition of the part 
which these stresses play in the properties of gases shows, or at least suggests, the 
possibility that the phenomena of ether which we observe may depend largely upon 
analogous stresses. 
Appendix. 
(Added December, 1870). 
Note 1. 
Since the reading of this paper I have had my attention called to a paper by W. Eeddersen (“ Uber 
Thermodiffusion von Gasen,” Pogg. ‘ Ann.,’ 1873). Eeddeesen made some experiments, and seems to have 
thought that he had discovered some such phenomenon. But the results he obtained were attributed by 
M. J. Violle to the presence of the vapour of water, against which no precautions appear to have been 
taken (‘ Journal de Physique,’ 1875, p. 90). That M. J. Violle was right there can be do doubt, for the 
results obtained are now seen to be much too large for the true results, and are similar to those which I 
obtained before I had succeeded in sufficiently drying the air. 
Note 2. 
Graham applied the term “ transpiration ” to the passage of gases through capillary tubes as distinguished 
from the passage of gases through larger tubes and through apertures in thin plates, and applied the 
term “ effusion ” to the passage of gases through minute apertures in thin plates. 
He did not apply either of these terms to the passage of gases through porous plates, because his 
experiments led him to conclude that the phenomena attending such passage were not the same as the 
phenomena attending either of the former, but were somewhere between the two. 
By the fuller light thrown on to the subject by this investigation it appears that in the limit, when 
the tubes and holes are small enough according to the condition of the gas, the laws of transpiration 
are strictly the same as those of effusion, the theory of the phenomena being the same. Hence the 
continued use of two names appears to be unadvisable. 
The term “ transpiration” has been chosen in preference to “effusion,” because it is found that as the 
passages become coarser, according to the condition of the gas, the law of the passage of gas through 
porous plates is still in strict accordance with the law of the passage through tubes, showing that the 
passages are of the nature of tubes rather than thin plates. 
