SOLAR AND PLANETARY EVOLUTION/ 



Everything of which we have any knowledge is the re- 

 sult of growth or progress, in one way or another, accord- 

 ing to law. I suppose that no reasonable person, who is ac- 

 quainted with the facts, would pretend that the earth or 

 the universe is any less the result of a regular process of 

 development than a tree. 



The question before us is, How did the world begin ? How 

 Avere the heavens framed ? Any answer that may be made to 

 this question must take into account what, broadly speaking, 

 may be termed the nebular theory. But we need not confine 

 ourselves to the consideration of the theory of Laplace. I 

 speak just now of a nebulous beginning in a general sense, 

 without special reference to any particular hypothesis. 

 What we want to get, first of all, is a clear conception of 

 how the solid earth, the sun, and all the substantial bodies 

 by which we are surrounded, were once nebulous masses, as 

 thin as air. 



Perhaps we can best get at it in this way. Suppose we 

 could take a puff of steam just as it came from the boiler, 

 and remove it, freed from all external influences, into space. 

 What would happen ? At first, perhaps, owing to its great 

 heat, the steam would be invisible. But the intense cold 

 of surrounding space would cause it to radiate its heat, and 

 it would condense until it became visible as a cloud of vapor. 

 The two great constructive forces of the universe, heat and 

 gravitation, would carry on a contest in the little puff of 

 steam ; heat pushing outward, gravitation drawing inward. 

 But gravitation is the more persistent force, and as the heat 



* Synopsis, from stenographer's notes, corrected by the lecturer. Copyright, 

 1889, by The New Ideal Publishing Company. 



The thanks of the Publishers, and of the Brooklyn Ethical Association, are 

 due to Messrs. D. Appleton & Company for the use of the illustrations on pages 

 59, 63, 64, 65, 66, 68 and 69. 



The cuts illustrating Laplace's theory and Faye's hypothesis were kindly fur- 

 nished by Mr. Serviss — the former having been devised by Professor George 

 W. Coakley, for his lecture on "The Nebular Hypothesis of Laplace," read be- 

 fore the American Astronomical Society. 



