HYPOTHESES. 27 



unstratined rocks, while there is the strongest reason 

 to believe that any terrestrial agent capable of ope- 

 rating on so large a scale would not have remained 

 unknown. 



The celebrated speculation of Laplace, now very 

 generally received as probable by astronomers, con- 

 cerning the origin of the earth and planets, partici- 

 pates essentially in the strictly inductive character of 

 modern geological theory. The speculation is, that 

 the atmosphere of the sun originally extended to the 

 present limits of the solar system ; from which, by 

 the process of cooling, it has contracted to its present 

 dimensions ; and since, by the general principles of 

 mechanics, the rotation of the sun and of its accom- 

 panying atmosphere must increase in rapidity as its 

 volume diminishes, the increased centrifugal force 

 generated by the more rapid rotation, overbalancing 

 the action of gravitation, would cause the sun to aban- 

 don successive rings of vaporous matter, which are 

 supposed to have condensed by cooling, and to have 

 become our planets. There is in this theory no 

 unknown substance introduced upon supposition, nor 

 any unknown property or law ascribed to a known 

 substance. The known laws of matter authorize us 

 to suppose that a body which is constantly giving out 

 so large an amount of heat as the sun is, must be 

 progressively cooling, and that by the process of cool- 

 ing 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 its 

 atmosphere extended much farther than at present, 

 and we are entitled to suppose that it extended as far 

 as we can trace those effects which it would naturally 

 leave behind it on retiring ; and such the planets are. 

 These suppositions being made, it follows from known 



