Permanent Colours of pake Bodies. 189 



*' afbivity from the particles of light which enter 

 " their compofition." 



He obferves that " Bodies and light a6t mu- 

 *' tually upon one another, that is to fay, bodies 

 *' upon light in emitting, refieding, refradting 

 *' and infledling it, and light upon bodies by 

 ** heating them, and putting their parts into a 

 *' vibrating motion wherein heat conlifts."* And 

 that the mutual action between light and inflam- 

 mable bodies is much ftronger» than between 

 lioht and other bodies. 



In clafling feveral kinds of bodies, according 

 to their refradive powers, heinflances " Selenite, 

 '' rock cryftal, ifland cryftal, vulgar glafs, and 

 " glafs of antimony, which are terreftrial ftony 

 *' concretes."! To thefe fubftances which confilt 

 principally of earth, and have the weakeft refrac- 

 tive powers, he thus oppofes the following inflam- 

 mable fubftances ; " The refradion of camphire, 

 *' oil olive, linfeed oil, fpirit of turpentine and 

 " amber, which are fat,;}; fulphureous, un(fluous 

 " bodies, and a diamond^ which prchahly is an 

 " un^uous fuhjlance coagulated, have their refrac- 

 ** tive powers in proportion to one another as 



• Newton. Opt. Qu. ad Calc, 



t lb. L. II. Part. HI. Prop. X. 



X Sir Ifaac Newton, according to the cuftom of his time, 



sfes the word fulphureous, unftaous, &c. to fignify what 



later chymical writer* exprefs by the terms phlogiftlc or 



-inflammable. 



" their 



