22 
DE. G. H. BRYAN ON THE KINETIC THEORY 
excess of the mean. Tlie mean itself' may be increased, but as the present calculations 
are based on tlie hypothesis that the mean translational energy is projDortional to the 
temperature, such an increase would be equivalent to an assumed increase of the 
temperature. 
Now if the molecular distribution in the rqjper regions of the atmosphere were 
dejjendent entirely on encounters between the molecules taking place in those regions, 
the rare occurrence of such encounters would no douht practically prevent their having 
any appreciable effect in bringing about the normal or “ tt ” distribution; and the 
distribution, if it followed any law at all, would be determined by any disturbances 
whose aggregate effect was sufEciently marked to give rise to a “ 8 ” function. 
But it is my contention that the molecules in the upper regions in describing free 
paths frequently descend to the denser portions of the atmosjDhere where they collide 
with other molecules, and their place is supplied by molecules shot up from these 
lower regions. The causes tending to bring about the law of distribution investigated 
in this paper are therefore not of infrequent occurrence, and we are justified in 
assumiiip’ the effects of the “ 77 ” function to be considerable even in the hig-her strata 
of the atmosphei'e. 
Going now to the disturbing causes, the following include the principal ones 
suggested by Dr. Stoney, viz. :— 
(«) Tides in the atmosphere. 
(h) Convection currents. 
(c) Solar radiation. 
(d) Atmospheric storms and the transferences of energy associated with them. 
(c) Electrical disturbances giving rise to “ prominences.” 
Of these causes, tlie effects of tide-generating forces still remain to be dealt with 
in a subsequent investigation. The same applies to convection currents, except so 
far as their general effects, introducing a temperature gradient, have been briefly 
mentioned. The effect of solar radiation is to increase the temperature of the gas on 
which it falls. But I freely admit that given a sufficiently high temperature helium 
\vill escape. Yet in his 1897 paper"^'" Dr. Stoney assumes so low a temperature as 
— 6G° C. or 207” absolute, while with considerably higher temperatures I find helium 
permanent. The question as to how the energy of solar radiation is absorbed by 
molecules and converted into kinetic energy of translation is one of great difficulty, 
and cannot be adequately discussed here, but if the view be accepted that the 
increase of translational kinetic energy takes place entirely at encounters, the effects 
of solar radiation in the upper layers of the atmosphere would seem to be small. Of 
the last two causes, if storms occasionally give rise to exceptionally high temperatures, 
it is clear again that our assunqjtions as to temperature conditions must be modified. 
Lastly, if the escape of gases be attributed to jets or prominences, the problem is 
‘Scientific Transactions of the Royal Dublin Society,’ vol. 6, p. 13. 
