234 COSMOGONIC HYPOTHESES. 



evolution, and that possibly together they lead in some way to 

 approximate cycles of an extent in time and space so far not 

 contemplated." (p. i6o.) 



LuNN. — " Geophysical Theory Under the Planetesimal Hypo- 

 thesis.'" 



In this paper, if I grasp aright the meaning, the author 

 shows, by adopting plausible laws of compression and density, 

 that it is only small bodies that can be very dense, which is borne 

 out so far as they go by astronomical observations ; thus we have 



Cox. — " Beyond the Atom." 1913. 



" One pound of the emanation would, at its maximum in- 

 tensity, radiate energy at the rate of about 10,000 horse-power. 

 This large emission of energy from the radio-active bodies throws 

 an interesting light on two questions which have long been the 

 subject of controversy, the age of the Earth and the source of the 

 heat of the Sun." (p. 109.) 



Period of fall of Uranium to half -value f). 000 ,000,000 years. 

 (Table, p. 91.) 

 Kelvin (and Green). — "The Prol)lem of a Spherical Gaseous 



Nebula. Trans. R. S. of Pldiii., 1907-1908. 



" It is scarcely possible to conceive that any fluid composed 

 of the chemical elements known to us, could be gaseous in the 

 Sun's atmosphere at depths exceeding 100 kilometres." (p. 268.) 



Kelvin called a gas in which 7, the ratio of the specific heats, 

 is greater than i ^ a gas of species P ; and it is almost certain that 

 all monatomic gases have 7 =r 1 2.. 



" We see that the central temperature of a globe of gas P in 

 equilibrium increases through gradual loss of heat by radiation 

 into space. \Ve then see also that the internal energy of a globe 

 of gas P, continuing in a condition of approximate equilibrium, 

 while heat is being radiated away across its boundary, would go 

 on increasing, and the work done by mutual gravitation of its 

 parts would go on increasing till the gas in the central regions 

 becomes too dense to obey Boyle's Law." . (p. 281.) 



In the above statement no account is taken of any possible 

 liberation of atomic energy, but, even without this, it is evident 

 that the underlying idea of contraction is at fault, and that a de- 

 crease of internal temperature and increase of size could go on 

 together. 



So far as observation goes, the evidence is in favour of the 

 latter view. Although hardly supplying an exact parallel, it is 



* Uncertain ; Stebbins gives Mass 0.55, Density 002 



