TE SMNOM Mi INE ROAR LLY PO DHE SLS 59 
molecular velocities essentially correct. However, the kinetic 
theory is perhaps not yet beyond its trial stages, though it is 
probable that the essential postulates involved in the doctrine 
of molecular velocities are true whatever the precise interpreta- 
tion of the facts may be. There is an accord between the 
doctrine and the facts in the solar system which strengthens this 
conviction. There is an absence of atmosphere from all satel- 
lites and asteroids, so far as can be determined. The planet 
Mercury has little or no atmosphere. The small planet Mars 
has but a thin atmosphere. The Earth and Venus have consid- 
erable gaseous envelopes, while Jupiter and Saturn appear to 
have vast and deep atmospheres; in short, there is a general 
correspondence between the mass of the atmosphere and the 
gravitative competency of the body. In still further evidence is 
the essential absence of the lightest gases, hydrogen and helium, 
from the earth’s atmosphere.*. The tormer, to be sure, is chem- 
ically active, but the latter is very inert. 
Notwithstanding the apparent strength of the molecular 
argument, other tests, based on quite independent grounds, are 
desirable. The more is this true since a modification of the form 
of the Laplacian hypothesis in which a lower temperature and a 
meteoroidal state are postulated deprives the molecular argu- 
ment of much of its bearing. It is true that this change in the 
hypothesis when carried out consistently in its full application 
permits, if, indeed, it does not require, a revision of some of the 
fundamental doctrines of current geology, such as the former 
molten state of the earth and the long train of doctrines that 
hang upon this. So profound is the influence of this primal con- 
ception of a molten earth upon the dynamical conceptions and 
historical interpretations of the earth’s evolution that every 
source of light bearing upon it has an importance we can 
scarcely realize at present. 
* “On the Cause of the Absence of Hydrogen from the Earth’s Atmosphere and 
of Air and Water from the Moon,” by Dr. Johnstone Stoney, Royal Dublin Society, 
1892. Also “Of Atmospheres upon Planets and Satellites,” by the same, Trans. Roy. 
Dublin Society, Vol. VI, Part 13, Oct. 25, 1897; also ‘A Group of Hypotheses Bear- 
ing on Climatic Changes,” by T.C. Chamberlin, Jour. GEOL., Vol. V, No.7, Oct.- 
Nov., 1897. 
