92 History of Luminescence 



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 Martins 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 sup- 

 pose, 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. ^ 



In discussing the " Colours of Light " (section 4) , Bacon wrote: 

 " No green flames are observed: what most inclines to greenness, is 

 that of the glow-worm." 



Regarding " Cognations [resemblances] and Hostilities [antago- 

 nisms] of Light " (Section 12) Bacon wrote: 



Light, as far as regards its production, has most of all cognation with 

 three things, heat, tenuity, and motion. . . . The flame of spirit of wine 

 or of an ignis fatuus, has a much feebler heat than red-hot iron, but a 

 stronger light. Glow-worms and the dews of salt water, and many of the 

 things which we mentioned throw out light, yet are not hot to the 

 touch. . . . 



But hostilities of light, or privations, if any like the term better, occur 

 not. However, as is exceedingly probable, the torpor of bodies, in their 

 parts, is very inimical to light. For almost nothing gives light that is not 

 in its own nature remarkably mobile, or excited by heat, or motion, or 

 vital spirit. 



In the Advancement of Learning (1605) , limiinescences were 

 again mentioned, in connection with a discussion of light and the 

 human soul and sensation. Bacon wrote: ^ 



And men ought 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 



' Topics of inquiry concerning light and the matter of light. In Basil Montague, 

 Esq., The works of Francis Bacon 15: 82-87, London, 1834. 



* Book IV, Chap. 3, p. 131. Edition of J. E. Creighton, London and New York, The 

 Colonial Press. 1900. 



