THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FIFTH SERIES.] 



JULY 1878. 



I. On the Origin of Neb alee. 

 By James Croll, LL.D., F.R.S* 



THE object of the present communication is to examine 

 the bearings of the modern science of energy on the 

 question of the origin of nebulse, and in particular to con- 

 sider the physical cause of the dispersion of matter into stellar 

 space in the nebulous form. In doing so I have studiously 

 avoided the introduction of mere hypotheses and principles not 

 generally admitted by physicists. These remarks may be 

 necessary, as the title of the paper might otherwise lead to the 

 belief that it is on a speculative subject lying outside the 

 province of the physicist. 



The question of the origin of nebulas is simplified by the 

 theory, now generally received, that stars are suns like our 

 own, and that nebulae are in all probability stars in process 

 of formation. The problem will therefore be most readily 

 attacked by considering, first, the origin of our sun, as this 

 orb, being the one most accessible to us, is that with which we 

 are best acquainted. 



By the origin of the sun I do not, of course, mean the origin 

 of the matter constituting the sun — this being an inquiry with 

 which the physicist has nothing whatever to do — but simply 

 its origin as a sun, i. e. as a source of light and heat. Our 

 first question must therefore be, What is the origin of the 

 sun's heat ? From what source did he derive that enormous 

 amount of energy which in the form of heat he has been dis- 



* Communicated by the Author. 

 Phil Mag. S. 5. Vol. 6, No. 34. July 1878. B 



