80 THEORY OP LIGlfT AND COLOURS. 



con fi derations fo much tlie more of their attention, as they arr^ 

 pear to coincide more nearly with Newton's own opinions. 

 For this reafon, after having briefly ftated each particular po- 

 rtion of my theory, I fliall collect, from Newton's various 

 writings, fuch paflages as feem to be the mod favourable to its 

 admifiion ; and, although I mail quote fome papers which may 

 be thought to have been partly retracled at the publication of 

 the optics, yet I fliall borrow nothing from them that can be 

 fuppofed to militate againft his maturer judgment. 



HYPOTHESIS I. 



A luminiferous Ether pervades the Univerfe^ rare and elaftk in a 

 high degree* 



Pajjiiges from Neivtorii 

 Hypottu I. " The hypothecs certainly has a much greater affinity with 



dic'ethef^ * " hia 0Wn " that is ' Dr " Hooke ' s > " hypothecs, than he feems 

 " to be aware of; the vibrations of the ether being as ufeful 

 " and neceflary in this as in his." (Phil. Tranf. Vol. VII* 

 p. 5087. Abr. Vol. I. p. 14-5. Nov. 1672.) 



" To proceed to the hypothecs : firit, it is to be fuppofed 

 " therein, that there is an ethereal medium, much of the fame 

 " conftitution with air, but far rarer, fubtler, and more itrongly 

 " elaftic. It is not to be fuppofed, that this medium is one 

 * e uniform matter, but compounded, partly of the main phlegm 

 " matic body of ether, partly of other various ethereal fpirits, 

 " much after the manner that air is compounded of the phleg- 

 '* matic body of air, intermixed with various vapours and ex* 

 " halations : for the electric and magnetic effluvia, and gravi- 

 " tating principle, feem <o argue fuch variety." (Birch. Hid. 

 of R.S. Vol. III. p. 249. Dec. 1675.) 

 Arguments pro- " * s not ^ ie ^ eat (of the warm room) conveyed through the 

 poled by New- " vacuum by the vibrations of a much fubti+er medium than 



[be etiu P ° rt ° f " air ■ And is not this medium the farae with that medium by 

 " which light is refracted and reflected, and by whofe vibra* 

 " tions light communicates heat to bodies, and is put into fits 

 " of eafy reflection, and eafy tranfmiflion ? And do not the vi* 

 " brations of this medium in hot bodies, contribute to the in* 

 " tenfenefs and duration of their heat? And do not hot bodies 

 " communicate their heat to contiguous cold ones, by the vi- 

 " brations of this medium propagated from them into the cold 



" ones I 



