56 TERRESTRIAL ADAPTATIONS. 



volving in its own plane as that does, each part 

 of both the flat surfaces would have the same 

 exposure to the sun, and the same temperature, 

 so far as the sun's effect is concerned. There is 

 no obvious reason why a planet of such a form 

 might not be occupied by animals and vegetables, 

 as well as our present earth ; and on this suppo- 

 sition the climate would be every where the same, 

 and the whole surface might be covered with 

 life, without the necessity of there being any 

 difference in the kind of inhabitants belonging 

 to different parts. 



Again, it is possible to conceive arrangements 

 according to which no part of our planet should 

 have any steady climate. This may probably be 

 the case with a comet. If we suppose such a 

 body, revolving round the sun in a very oblong 

 ellipse, to be of small size and of a very high 

 temperature, and therefore to cool rapidly ; and 

 if we suppose it also to be surrounded by a large 

 atmosphere, composed of various gases ; there 

 would, on the surface of such a body, be no ave- 

 rage climate or seasons for each place. The 

 years, if we give this name to the intervals of 

 time occupied by its successive revolutions, would 

 be entirely unlike one another. The greatest 

 heat of one year might be cool compared with 

 the greatest cold of a preceding one. The great- 

 est heats and colds might succeed each other at 

 intervals perpetually unequal. The atmosphere 



