THE ORGANIC AND THE INORGANIC 315 



of stages, each phase of the series being marked by a 

 progressive decrease of diversity, that is, by some 

 degradation of energy. Two main series of hypotheses 

 accounting for the present condition of the universe 

 seem to have been the result of physical investigation : 

 (i) the origin of discrete solar and planetary bodies 

 by a process of condensation of a gaseous nebular sub- 

 stance ; and (2) the origin of the same systems by 

 aggregations of meteoric dust. Plausible as is the 

 nebular hypothesis on first consideration, it fails when 

 it is subjected to minute analysis. What is a gaseous 

 nebula ? It is a mass of heated vapour contracting 

 by the mutual gravity of its parts as its molecules lose 

 their heat by radiation — so the hypothesis states. 

 But it has been pointed out that we cannot be certain 

 that the gaseous nebulae known to astronomy are hot, 

 or even that they gravitate. The great nebula in Orion, 

 it is stated, is at an enormous distance from us, and 

 making a minimal estimate of this distance the volume 

 of the nebula must still be incredibly great. There are 

 good reasons for believing that the mass of the visible 

 universe cannot be greater than that of a thousand 

 million of suns such as our own. Assuming that all this 

 matter is contained in the great nebula in Orion (and 

 obviously only a small portion of it can be so contained) , 

 we find on calculation that the " gas " so formed would 

 be much less dense than even the trace of gas contained 

 in a high vacuum artificially produced. 1 How, then, can 

 we speak of such a body as this nebula as an extended 

 mass of hot gas, cooling and gravitating as it loses heat ? 

 Even on the other hypotheses, those of the forma- 

 tion of discrete suns and planets by the aggregation of 

 meteoric dust, and the compensatory dispersal of such 



1 Its density would be -g gth that of our atmosphere. 



