COSMOGONIC HYPOTHESES. 235 



well known that tlie gaseous envelopes of comets contract as they 



approach the Sun. 



Newcomb. — "The Stars: A Study of the Universe." 1902. 



" A very remarkable case is that of ^ Orionis. It has a 

 minute companion at a distance of 2.5". VVere it a model of the 

 Sun, a companion at this apparent distance should perform its 

 revolution in 14 years. But, as a matter of fact, the motion is so 

 slow that even now, after 50 years of observation, it cannot be 

 determined with any precision. It is probably less than o.i" in a 

 year. The number expressing the comparison of the density and 

 surface brilliancy of this star with those of the Sun is probably 

 less than 0.000 1. The general conclusion to be drawn is obvious. 

 The stars in general are not models of our Sun." 1 p. 200. ) 

 Newcomb. — " Popular Astronomy." 1882. 



" Then a mathematical computation of the attractive i)ower 

 exerted by such a system of masses (500.000,000 sun-masses) 

 shows that a body falling from an infinite distance to the centre 

 of the system would acquire a velocity of 25 miles a second. ' 

 (p. 501.) 



This calculation does not seem to be correct, but it serves to 

 show how impossible it is for the potential energy of a nebula 

 composed of nebulium, lielium and hydrogen to be changed by 

 gravitation into the radio-active and other atomic energies of 

 heavy atoms. The velocity with which a small mass falling from 

 rest at an infinite distance would strike the Sun is 380 miles a 

 second. This means that a gram falling into the Sun would 

 generate 44,844 calories; this is but i/50,oooth of that evolved' 

 by radium. 

 Perry. — " The Life of a Star." " Nature." 1899, July 13. 



" Assumptions like those of Homar Lane and Ritter may 

 lead to results which are altogether wrong. . . Homar 



Lane, Lord Kelvin. Ritter and all people who have tried to make 

 exact calculations, iiave assumed that the stuff of which a star is 

 composed behaves as a perfect gas in a state of convective equili- 

 brium. . . . I)Ut if we api^ily our results to the Sun we find 

 that at its centre there is a density 33. that is, 50 per cent, greater 

 than the ordinary density of platinum. It seems to me that specu- 

 lation on this basis of perfectly gaSeous stuff ought to cease when 

 the density of gas at the centre of the star approaches o.t or one- 

 tenth of the density of ordinary- water in the laboratory. . . . 

 It seems to me that if a mass of this kind of gas (in which 7, the 

 ratio of its specific heats = i^) gravitates by itself from an in- 

 finite distance, it retains all its energy. But such gas must surely 

 be imagined to be radiating heat, as it is not at zero temperature. 

 Where can it get such heat? I come to the conclusion that there 

 must be atomic energy available somehow in it. . . .1 say 

 that no substance for which 7=: li can behave as a perfect gas." 



Kelvin's remarks on and his endorsement of Professor 

 Perry's conclusions will be found in Nature, 1907, February 14. 



