180 ADVANCEMENT OP LEARNING. [BOOK IV. 



of light. Its radiations, indeed, are treated, but not ita 

 origin ; and the ranking of perspective with mathematics 

 has produced this detect, 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 

 rraperstitiously 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 after 

 wards 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 contempla 

 tions a little, and inquire into the properties common to all 

 lucid bodies, as this relates to the form of light ; how im 

 mensely 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 spark 

 ling 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 or breaking ; the sweat 

 of a horse hard ridden, &c. Men have understood so little 

 of this matter, that most imagine the sparks, struck betwixt 

 a flint and steel, to be air in attrition. But since the air 

 ignites not with heat, yet apparently conceives light, whence 

 owls, cats, and many other creatures see in the night (for 

 there is no vision without light), there must be a native light 



