pron 
LXVII. 
OF ATMOSPHERES UPON PLANETS AND SATELLITES. 
By G. JOHNSTONE STONEY, M.A., D.8c., F.R.S. 
[Published in extenso in Transactions, vol. vi., Part 13, November, 1897.] 
[ Asstract. | 
In a Paper “ On the Physical Constitution of the Sun and Stars,” 
in No. 105 (1868) of the Proceedings of the Royal Society, 
Dr. Johnstone Stoney applied the Kinetic Theory of Gas to the 
interpretation of some of the phenomena of atmospheres. In it 
he explained the conditions which, under that theory, limit the 
height to which an atmosphere will range, and showed that the 
lighter constituents of an atmosphere will overlap the others. He 
subsequently extended the investigation in a series of communi- 
cations to the Royal Dublin Society, of which the earliest was 
in 1870; and he has given an account of these extensions in 
the Memoir of which this is an abstract—see Scientific Transactions 
of the Royal Dublin Society, vol. vi. p. 805, “ Of Atmospheres 
upon Planets and Satellites.” 
Dr. Stoney explains the absence of hydrogen and helium from 
the Earth’s atmosphere, and the absence of all known constituents 
of an atmosphere from the Moon, by showing that, in accordance 
with the Kinetic Theory, these gases are so cireumstanced upon 
the Earth and Moon that the velocities which their molecules can 
occasionally reach, suffice to enable the gas gradually to driit 
away; and he further arrives at the conclusion that the same theory 
implies that the vapour of water cannot be a constituent of the 
atmospheres of either Mercury or Mars. 
The conditions which prevail upon Mars are specially discussed. 
Since water cannot be present, nitrogen, argon, and carbon dioxide 
are suggested as the most probable constituents of its atmosphere. 
Of these the most condensible is carbon dioxide, and to it are 
referred the snow-caps which are formed alternately on the north 
