CC)SMO(X)NIC HYPOTHESES. 



By Ror.ERT T. A. Innes. 



The best known an 1 still the most widely accepted cosnio- 

 gonic theory is Laplace's nebular hypothesis. This hypothesis 

 was only put forward in a tentative manner by its author, 

 although on several occiisions he recurred to the subject. It is 

 proper to note that altlioug'h it is doubtful if anyone had ever 

 a greater facility for clolhing his ideas in mathematical formulae, 

 Laplace used none in ex: plaining the nebular hypothesis. Many 

 cosmogonies have been based on ideas not essentially different 

 from Laplace's, that is tl'ie condensation of a primitive nebula into 

 rings, which later disrupt into planets, whilst the central and 

 final condensation forms the central body or sun of the system. 

 The fission theory of the formation of satellites and double stars 

 from condensing bodies is closely connected with the nebular 

 hypothesis. 



Other sets of cosmogonies are indicated under the meteoric 

 or planetesimal hypothesis, and capture theory. Kant's cosmo- 

 gony was more general in that he postulated neither nebulous 

 matter nor meteors — merely matter. The nebular hypothesis 

 of Laplace, and its modifications by Faye, Darwin, See, and 

 others, seized on the popular mind, because it was not in too 

 marked discord with the theological teachings of the age, '* the 

 earth was without form, and void.'' Genesis i, 2. 



By the very mode of its existence, the human race can view 

 but a small part of the drama of nature. O 1 the surface of the 

 earth, thanks mainly to the geological record, the mode of the 

 evolution of flora and fauna, and the making of rocks is fairly 

 clear. Rut when we view not the surface of the earth, but bodies 

 outside the earth — the planets, stars and nebulae, oiu- interpre- 

 tation is not so easy. We cannot even say if the sun, and with 

 it the earth, is growing hotter or colder. We imagine the rhythm 

 of the universe is periodic, but until one period is completed — and 

 this the human race cannot live to see — how can we tell, nay, even 

 guess, the nature of its periodicity? The periodicity may ibe 

 complicated, is almost certainly more complicated than that of a 

 butterfly which goes through tjie stages of egg, caterpillar, 

 chrysalis, butterfly, etc., and what person could by the closest 

 inspection of, say, a millionth of any one of the sub-periods, egg, 

 caterpillar, chrysalis or butterfly, foretell the other sub- 

 periods? It is probably thus when we attempt to explain the 

 evolution of the stars. A\'hen Laplace wrote his nebular hypo- 

 thesis, facts were few-, the laws of thermodynamics had not even 

 been formulated, and modern chemistry was in its infancy. 

 Hypotheses without facts are not uncommon ; the Greek genius 

 loved hypotheses, but seemed to disdain facts, and the effects of 

 their examples are buried deep in the fibres of our mentality. 

 The fundamental assumption of the nebular hypothesis is that a 

 nebula can condense, i.e., not only get more dense, but even form 

 ultimately liquids and solids of various atomic weights. This 



