394 Intelligence and Miscellaneous Articles. 



salts of quinine. This blue, however, as is well known in the case 

 of quinine, is not of a single tint or refrangibility, but yields a con- 

 tinuous spectrum in which the more refrangible rays predominate. 



My attention was first drawn to the subject by observing that a 

 specimen of mixed asphalt, which is here largely used in the prepa- 

 ration of pavements, yielded a light-yellow solution with alcohol 

 which fluoresced blue, and an orange solution with turpentine which 

 fluoresced green. It at once occurred to me that the green colour 

 was simply due to the absorptive action of the coloured solution, 

 and not to the development of green rays. Examined with the 

 spectroscope, the seemingly green fluorescence showed no increase 

 in the green or yellow part of the spectrum as compared with the 

 blue fluorescence, but only an absorption of the red and violet ends. 

 When, however, a piece of fluorescing canary glass or solid nitrate 

 of uranium was examined, the green light was (as is well known) 

 largely augmented. I also found that when, by filtration through 

 animal charcoal, the solution in turpentine was reduced in colour, 

 the green tint of the fluorescence disappeared in a corresponding 

 degree. This alone, however, would have proved nothing, as a 

 green fluorescing matter might have been absorbed by the charcoal ; 

 but in connexion with the spectroscopic result it was of interest. 



I next took up for examination the tincture of turmeric. This is 

 set down in standard works, such as those of Du Moncel and Bec- 

 querel, as fluorescing red. This solution, when concentrated, has a 

 rich orange-red colour ; and the jacket of a Geissler tube being filled 

 with it, all the light reaching the eye from the electric discharge 

 within is of a deep orange or red colour. If, however, the solution 

 is simply diluted until its colour is reduced to a rich yellow, the 

 fluorescence appears green. The same result follows from filtration 

 through bone-black, with a marked increase in the amount of fluo- 

 rescence visible as the light-absorbing colouring-matter is removed. 

 By continuing the decoloration until the liquid is colourless or of a 

 very light tint, its fluorescence is distinctly blue. 



The results with the spectroscope when it was applied to this 

 substance were the same as with the solution of asphalt. Such also 

 is the case with tincture of chlorophyl, which, when fresh and 

 green, gives apparently a green light, and when old and brown a 

 grey colour. 



Finally, I took up the nitrate of uranium, about which such con- 

 tradictory statements have been published. This salt in its solid 

 state gives a brilliant green fluorescence whose spectrum is figured 

 by Becquerel and abounds in green rays ; but in solution it gives a 

 very feeble fluorescence, far inferior to that of turmeric, and of no 

 more green tint than would be due to its yellow colour. So in fact 

 says also the spectroscope. 



From these results it would seem that the molecules of fluorescent 

 bodies in solution are not capable of restricting their vibrations to 

 limited ranges, but move at rates corresponding with all refrangibi- 

 lities, having simply an excess of the higher ones, though the same 

 substances in the solid state may act quite differently, as in the case 



