,[ 172 ] [Bock III. 



C I! A P. II. 

 OF THE NATURE OF LIGHT. 



Various Opinions on the ASivn cf Light. 'Theory of a vibrating jl/e- 

 dium\ fuppcrted by Dcfcartes, sV. Objections to this Theory. 

 Light conjijis of infinitely minute Particles projected from the luminous 

 Body. Inquiry refpeSling the Identity cf Light and Fire. Experi- 

 ments of Mr. Beyle. Why Light is not always accompanied with 

 Heat. Velocity cf Light. Light always moves in Right Lines. 

 Rarity of Light. Force or Momentum of Light. Mitchell's Expe- 

 riment. Inquiry bo=w far the Sun's Magnitude is diminijhed ly the 

 Emzjfion cf Light. Light fubjeft to the ordinary Laws of Nature. 

 Light attradtd by the Bolognian Phofphori.Tke fame Property 

 ia. Diamonds, and other Precious Stones. 



NUMEROUS opinions have fucceflively been 

 adopted concerning this wonderful fluid. It 

 has been fometirjnes'confkkred as a diftinct fubftance, 

 fqmetimes as a quality, fometimes as a caufe, fre- 

 quently as an effect; by fome regarded as a compound, 

 and by others as a fimple fubftance. Des Cartes and 

 other philofophers of high repute have imagined that 

 the fcnfation which we receive from light is to be at- 

 tributed entirely to the vibrations of a fubtile medium, 

 or fluid, which is diffufed throughout the tiniverfe^ 

 and which is put into action by the impulfe of the fun. 

 In this view they confider light as analogous to found, 

 which is known to depend entirely on the pulfations 

 of the air upon the auditory nerves; and in fupport of 

 this opinion, it has been even lately urged'*, ift. TKat 



* Sre Dr. Franklin's woiks; and Pro feller Boudoin's Memoir, 

 Tranji;c>lcni cf American Ace. dan*;., Ye!, i. 



fomc 



