M. E. Hagenbach J s Experiments on Fluorescence. Gl 



the substance studied exhibited in certain places a peculiar 

 absorption in addition to that corresponding to the fluorescence. 

 It is so, for example, with the aqueous solution of turnsol, 

 solution of purpurine in soda, and nitrate of uranium either 

 solid or dissolved. 



Spectra of the Light emitted by Fluorescence, or Fluorescence- 

 Spectra. — I have given particular attention to the study and 

 description of fluorescence-spectra, which are presented under 

 the most varied forms. I shall here notice only those which 

 appear to me of special interest. 



The different kinds of light already known to be emitted by 

 fluorescence present tbe greatest variety in their colours, accord- 

 ing as they are red, orange, yellow, green, blue, or violet ; but 

 it is only by spectral analysis that an exact idea can be obtained 

 of their composition. 



It is moreover established that there are very great differences 

 in the breadth of the fluorescence- spectrum. That of chlo- 

 rophyl has the least breadth ; it is so narrow that we might 

 almost suppose that the light thus emitted is a homogeneous 

 red. Those of thiomelic acid, fluor spar, and others, on the 

 contrary, exhibit a very great breadth ; the fluorescence-spectra 

 of these substances include rays belonging to the different 

 portions of the spectrum from the red to the violet. 



An interesting point to note is, that in a great number of 

 cases the fluorescence-spectrum offers a very unequal distri- 

 bution of luminous intensity : we have in them a series of 

 brighter bands, maxima. of luminous intensity, separated from 

 one another by other bands more or less obscure; it is right, 

 however, to remark that these bands are not sharply defined, 

 but pass gradually into one another; and the dark bands are 

 not absolutely black, but more or less shaded zones. I have 

 observed, for example, eight maxima in the fluorescence-spec- 

 trum of nitrate of uranium, six maxima in that of photene or 

 anthracene and in that of petroleum, five maxima with uranium 

 glass and the extract of lampblack, three very distinct with 

 solution of guaiacum, three less decided with fluoresceine, two 

 equally well-marked maxima with alcoholic solution of turnsol, 

 solution of orchil, and fresh solution of chlorophyl in ether, two 

 maxima also, but less clear, with oxide of brasiline, sulphate of 

 quinine, sesculine, and tincture of curcuma, and only one maxi- 

 mum (consequently no intermission in the intensity of the light) 

 with solution of morinc alum, naphthaline-rose, thiomelic acid, 

 and fluor spar. 



The difference in luminous intensity between the maxima and 

 minima in the fluorescence-spectra varies a great deal : the 

 maxima in the case of nitrate of uranium form very neat bands 



