Fluorescence 393 



phureus salt of a contrary nature " (oil of tartar per deliquium) , 

 an alkali, was added; also that a concentrated infusion of the wood 

 did not exhibit the phenomena too well. 



Although Kircher is often regarded as the discoverer of fluores- 

 cence in solution, Boyle really established two main chemical facts 

 regarding fluorescence of organic compounds— that the phenomenon 

 is most apparent in dilute solutions and is greatly affected by acids 

 and alkalies. The latter change results from the fact that an organic 

 compoimd is usually fluorescent when present as a salt, rather than 

 as either the free organic acid or base. These transformations can 

 be brought about by addition of acid or alkali. 



Boyle also observed that other materials exhibited different colors 

 by reflected and transmitted light, for example gold foil, which is 

 the color of gold by reflected and green by transmitted light. He 

 also called attention to the colors of thin films, soap bubbles and 

 glass, but of course these phenomena have nothing to do with 

 fluorescence. 



L. Nuguet (1705) claimed that he could detect the yellow but 

 not the blue color of an extract of " lignum nephriticum " and that 

 such behavior was of no special interest anyway, since the phe- 

 nomenon can be observed with " certain little pots of glass in which 

 jam is kept," 



Newton's observations were published in the famous " Letter con- 

 taining his New Theory about Light and Colors " in the Philo- 

 sophical Transactions (No. 80) for 1672. He wrote: ^ 



The odd Phaenomena of an infusion of Lignum Nephriticum, Leaf 

 Gold, Fragments of coloured glass, and some other transparently coloured 

 bodies, appearing in one position of one colour, and of another in 

 another, are on these grounds no longer riddles. For, those are sub- 

 stances apt to reflect one sort of light and transmit another; as may be 

 seen in a dark room, by illuminating them with similar or uncom- 

 pounded light. For, then they appear of that colour only, with which 

 they are illuminated, but yet in one position more vivid and luminous 

 than in another, according as they are disposed more or less to reflect 

 or transmit the incident colour. 



The subject was again alluded to in the first edition of the Opticks 

 (1705, Book I, part 2, proposition 11), where he used Lignum 

 Nephriticum infusion, among other tests, to make sure a beam of 

 white light reconstituted by a second prism from the many colors 

 produced on passing through a first prism, was really the same as 

 the original white light. Had Newton used the word " emit " 



M. Newton, Phil. Trans. 6: 3084, 1672. 



