28 INDUCTION. 



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 temperature, 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 agglo- 

 merate 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, ascer- 

 tained to be true, within certain small limits of error*. 

 There is thus, in Laplace's theory, nothing hypothe- 

 tical: it is an example of legitimate reasoning from a 

 present effect to its past cause, according to the 

 known laws of that cause ; it assumes nothing more 

 than that objects which really exist, obey the laws 

 which are known to be obeyed by all terrestrial 

 objects resembling them. The theory therefore is, as 

 I have said, of a similar character to the theories of 

 geologists ; inferior to them in certainty, in about the 

 same ratio as those are inferior to facts conclusively 

 established by a judicial inquiry. For, the uncertainty 

 whether the laws of nature which prevail on our earth 

 prevail in the whole solar system, is about equal to the 

 uncertainty whether the laws which prevail in our 



Cours de Philosophic Positive, ii., 378383. 



