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TOPICS OF INQUIRY CONCERNING LIGHT 

 AND THE MATTER OF LIGHT. 



i. Presence Tables. 



WE have first to note which are the substances, of whatever 

 kind, that generate light; as stars, fiery meteors, flame, 

 wood, metals, and other burning bodies, sugar in scraping 

 or breaking it, the glowworm, the dews of salt water when 

 it is agitated or scattered, the eyes of certain animals, some 

 sorts of rotten wood, large quantities of snow; perhaps the 

 air itself may possess a weak light adapted to the vision of 

 the animals which see by night; iron and tin, when put into 

 aqua fortis to be dissolved, boil, and without any fire pro 

 duce intense heat, but whether or not they give out any 

 light demands inquiry; the oil of lamps sparkles in very 

 cold weather; a kind of faint light is sometimes observed 

 in a clear night around a horse that is sweating ; around 

 the hair of certain persons, there is seen, though rarely, 

 also a faint light, like a lambent flamule, as occurred to 

 Lucius Martius in Spain ; there was lately found an apron 

 of a certain woman which was said to shine, yet only when 

 rubbed ; but it had been dyed in green, of which dye alum 

 is an ingredient, and it rustled somewhat when shining. 

 Whether alum shines or not when scraped or broken is 

 matter of inquiry; but, I suppose, it requires more violent 

 breaking, because it is firmer than sugar. In like manner, 

 some stockings shine whilst you are pulling them off, 

 whether from sweat or the dye of alum. 



ii. Absence Tables. 



We must also observe which are the substances that give 

 no light, yet have much similitude to such as do produce 

 it. Boiling water does not give light; air though unusually 

 heated does not give light ; mirrors and diamonds, which 

 so strikingly reflect light, give no light of their own. 



In this kind of instances we have also to consider dili 

 gently the instances migratory, namely, when light, as if 



