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volving in an orbit little different from itspresent orbit, and undergoing all those pe-riodical changes, upon which climate, tem-perature, vegetation, and animal life de-pend ?

3. The several planets are spheroidallike the earth ; therefore they have beenfluid: and they agree with the earth in somany other particulars, that physical astro-nomers do not hesitate in ascribing to botha common origin.

Dr. Herschel deduces from his observa-tions on Nebulae , that they consist of rareand luminous matter, gradually condensedin consequence of the attraction of densernuclei which they surround; if we maysuppose the heavenly bodies formed by thesame process, Comets , he thinks, would af-ford an example of an imperfect, Planetsof a complete condensation of such mat-ter.

The author of the Mechanique Celeste,has with becoming caution advanced a simi-lar hypothesis; he supposes that the matterof the solar atmosphere expanded by exces-