PROOFS, ILLUSTRATIONS, AUTHORITIES, ETC. in 



2. THE LAPLACIAN COSMOGONY. 



There is a great difference between inventing laws of nature to 

 account for classes of phenomena, and merely endeavouring, in con- 

 formity with known laws, to conjecture what collocations, now gone 

 by, may have given birth to individual facts still in existence. The 

 latter is the strictly legitimate operation of inferring from an ob- 

 served effect, the existence, in time past, of a cause similar to that 

 by which we know it to be produced in all cases in which we have 

 actual experience of its origin. This, Cor example, is the scope of 

 the inquiries of geology ; and the}' are no more illogical or visionary 

 than judicial inquiries, which also aim at discovering a past event 



by inference from those effects which still subsist We can 



conclude that a man was murdered, although it is not proved by the 

 testimon}'- of eye-witnesses, that a man who had the intention of 

 murdering him was present on the spot. It is enough if no other 

 known cause could have generated the effects known to have been 



produced The celebrated speculation of Laplace, now verv 



generally received as probable by astronomers, concerning the origin 

 of the earth and planets, participates essentially in the strictly in- 

 ductive character of modern geological theory The known 



laws of matter authorise us to suppose that a body which is con- 

 stantly giving out so large an amount of heat as the sun is, must 

 be progressively cooling, and that by the process of cooling it must 

 contract ; if, therefore, we endeavour, from the present state of that 

 luminary, to infer its state in a time long past, we must necessarily 

 suppose that it extended as far as we can trace those effects which 

 it would naturally leave behind on retiring; and such the planets 

 are. These suppositions being made, it follows from known laws 

 that successive zones of the solar atmosphere would be abandoned ; 

 that these would continue to revolve round the sun with the same 

 velocity as when they formed part of his substance ; and that they 

 would cool down, long before the sun himself, to any given tempe- 

 rature, and consequently to that at which the greater part of the 

 vaporous matter of which they consisted would become liquid or 

 solid. The known law of gravitation would then cause them to 

 agglomerate in masses, which would assume the shape our planets 

 actually exhibit ; would acquire, each round its own axis, a rotatory 

 movement ; and would in that state revolve, as the planets actually 

 do, about the sun, in the same direction with the sun's rotation, but 

 with less velocity, and each of them in the same periodic time which 

 the sun's rotation occupied when his atmosphere extended to that 

 point ; and this also M. Comte has, by the necessary calculations, 

 ascertained to be true, within certain small limits of error. There 

 is thus, in Laplace's theory, nothing hypothetical : it is an example 

 of legitimate reasoning from a present effect to its past cause, ac- 

 cording to the known laws of that cause ; it assumes nothing more 

 than that objects which really exist, obey the laws which are known 



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