LIGHT. 137 



were believed to prove that they have no appreciable atmos- 

 pheres. 



If it be admitted, or considered proved, that the sun and 

 planets have atmospheres- and little doubt now exists on this 

 point then the grounds upon which Wollaston founded his 

 arguments are untenable ; and there appears no reason why 

 the atmosphere of the different planets should not be, with 

 reference to each other, in a state of equilibrium. Ether, or 

 the highly-attenuated matter existing in the interplanetary 

 spaces, being an expansion of some or all of these atmos- 

 pheres, or of the more volatile portions of them, would thus 

 furnish matter for the transmission of the modes of motion 

 which we call light, heat, &c. ; and possibly minute portions 

 of these atmospheres may, by gradual changes, pass from 

 planet to planet, forming a link of material communication 

 between the distant monads of the universe. 



The view given above would approximate the theory of 

 the transmission of light by the undulations of ordinary mat- 

 ter to the other two theories, which equally suppose the non- 

 existence of a vacuum ; for, according to the emissive or 

 corpuscular theory, the vacuum is filled by the matter itself, 

 of light, heat, &c. ; according to the ethereal, it is filled by 

 the all-penetrating ether. Of the existence of matter in the 

 interplanetary spaces we have some evidence in the diminish- 

 ing periods of comets ; and where, from its highly attenuated 

 state, the character of the medium by which the forces are 

 conveyed cannot be tested, the term ether is a most appropri- 

 ate generic name for such medium. 



Newton has some curious passages on the subject matter 

 of light. In the ' Queries to the Optics ' he says : 

 ^ + Are not gross bodies and light convertible into one 

 another, and may not bodies receive much of their activity 

 from the particles of light which enter their composition? 

 * * * The changing of bodies into light and light into 

 bodies is very conformable to the course of nature, which 



