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capital, and very extensive use : for the ignorance of some an- 

 cient philosophers in this point, so far obscured the light of 

 reason, that they thought there was a soul indifferently infused 

 into all bodies ; nor did they conceive how motion of election 

 could be caused without sense, or sense exist without a soul. 



That the form of light should not have been duly inquired 

 into, appears a strange oversight, especially as men have be- 

 stowed so much pains upon perspective : for neither has this art, 

 nor others, afforded any valuable discovery in the subject of 

 light. Its radiations, indeed, are treated, but not its origin ; and 

 the ranking of perspective with mathematics has produced this 

 defect, with others of the like nature, because philosophy is thus 

 deserted too soon. Again, the doctrine of light, and the causes 

 thereof, have been almost superstitiously treated in physics, as a 

 subject of a middle nature, betwixt natural and divine ; whence 

 certain Platonists would have light prior to matter itself: for 

 they vainly imagined, that space was first filled with light, and 

 afterwards with body ; but the Scriptures plainly say, that the 

 mass of heaven and earth was dark before the creation of light. 

 And as for what is physically delivered upon this subject, and, 

 according to sense, it presently descends to radiations, so that 

 very little philosophical inquiry is extant about it. And men 

 ought here to lower their contemplations a little, and inquire 

 into the properties common to all lucid bodies, as this relates to 

 the form of light ; how immensely soever the bodies concerned 

 may differ in dignity, as the sun does from rotten wood, or 

 putrefied fish. We should likewise inquire the cause why some 

 things take fire, and when heated throw out light, and others 

 not. Iron, metal, stones, glass, wood, oil, tallow, by fire yield 

 either a flame, or grow red-hot. But water and air, exposed 

 to the most intense heat they are capable of, afford no light, nor 

 so much as shine. That it is not the property of fire alone to 

 give light ; and that water and air are not utter enemies thereto, 

 appears from the dashing of salt-water in a dark night, and a 

 hot season, when the small drops of the water, struck off by 

 the motion of the oars in rowing, seem sparkling and luminous. 

 We have the same appearance in the agitated froth of the sea, 

 called sea-lungs. And, indeed, it should be inquired what 

 affinity flame and ignited bodies have with glow-worms, the 

 Luciola, the Indian fly, which casts a light over a whole room ; 

 the eyes of certain creatures in the dark ; loaf-sugar in scraping 



