122 CORRELATION OF PHYSICAL FORCES. 



Sir W. Herschel's observations go to prove that the sun 

 and Jupiter have dense atmospheres, while Wollaston's were 

 believed to prove that they have no appreciable atmospheres. 

 The results of recent observations with the spectroscope are in 

 favour of the former conclusion ; the chromosphere being 

 found to extend far beyond the defined disc of the sun. 



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, 

 which term we may apply to the highly-attenuated matter 

 existing in the interplanetary spaces, being an expansion of 

 some or all of these atmospheres, or of the more volatile por- 

 tions 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 

 accretions and subtractions, pass from planet to planet, form- 

 ing a link of material communication between the distant 

 monads of the universe. 



The assumption of the universal presence of matter is 

 common to the theory of the transmission of light by the 

 undulations of ordinary matter and to the other two theories, 

 which equally presuppose 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 diminishing 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 very admissible 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 



