98 



And so we see that all the heavenly bodies shine 

 either from incandescence of their substance, as is the 

 case with asteroids and cosmic clouds; or in consequence 

 of combustion as in the case of suns; or by reflected 

 solar light and combustion of an atmosphere as in the 

 case of planets and cerolites; or by mutual action of two 

 bodies as in the case of double -stars. We must now con- 

 tinue our study of luminous phenomena by some expla- 

 nation of the double-star. 



