THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FOURTH SERIES.] 



JUNE 1870. 



LVII1. A Theory of Nebula and Comets, By A. S. Davis, B.A., 

 Mathematical Master, Leeds Grammar School. 



To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 

 \^ILL you allow me to lay before your readers a theory re- 

 garding nebula? and comets which I believe is in a great 

 degree new, and which appears to me to afford a satisfactory ex- 

 planation of the phenomena observed in those remarkable bodies? 



The theory may be stated as follows : — There exist in space 

 large masses of matter in a gaseous, non-luminous, and there- 

 fore invisible state. This matter is necessarily very rare, because 

 there is no solid nucleus to condense it by its attraction. As 

 long as a mass of such matter remains by itself, it continues 

 gaseous, non-luminous, and invisible. It will, however, some- 

 times happen that two masses of gas having a chemical affinity 

 for each other rush together under the influence of their mutual 

 gravitation. When this occurs, chemical combination will take 

 place, with a consequent evolution of light and heat, and a ne- 

 bula will begin to be formed. Chemical action will only take 

 place where the gases become mixed — that is, about their common 

 bounding surfaces ; and the greater part of the matter will remain 

 invisible. The apparent shape, then, of a nebula will by no 

 means indicate the real shape of all the matter composing it, but 

 will rather reveal the form of the common bounding surfaces of 

 the different masses of gas. 



The gases, so long as they remain separate, cannot condense 

 into a liquid or solid state ; but the compound formed by the 



Phil. Mag. S. 4. Vol. 39. No. 263. June 1870. 2 D 



