222 PROGRESS OF SCIENCE IN THE CENTURY. 



would fit in well with the evolutionary theory, being 

 suggestive of community of origin. 



Corroboration may also be found in Helmholtz's 

 shrinkage theory (previously noted) of the origin 

 and maintenance of solar energy, for it leads us 

 back to a larger and less condensed sun, and thence 

 to one larger still, until finally we approach some- 

 thing like Laplace's primitive nebula. " We can 

 reason back to the time when the sun was sufficiently 

 expanded to fill the whole space occupied by the solar 

 system and was reduced to a great glowing nebula. 

 Though man's life, the life of the race perhaps, is 

 too short to give us direct evidence of any distinct 

 stages of so august a process, still the probability is 

 great that the nebular hypothesis, especially in the 

 more precise form given to it by Roche, does repre- 

 sent broadly, notwithstanding some difficulties, the 

 succession of events through which the sun and plan- 

 ets have passed." * 



" So little is, however, known of the behaviour of a 

 body like Laplace's nebula when condensing and rotat- 

 ing that it is hardly worth while to consider the details 

 of the scheme, and that Laplace himself did not take 

 his hypothesis nearly so seriously as many of its ex- 

 pounders, may be inferred from the fact that he only 

 published it in a popular book, and from his remarkable 

 description of it as " these conjectures on the formation 

 of the stars and of the solar system, conjectures which 

 I present with all the distrust which everything which 

 is not a result of observation or of calculation ought 

 to inspire." f 



Meteoritic Hypothesis. — We have already alluded 

 to the speculation, which is now particularly asso- 



* Sir W. Huggins. Rep. Brit. Ass. for 1891, p. 20. 



t Arthur Berry. Short History of Astronomy, 1898, p. 322. 



