164 Fluorescence and Absorption. By H. 0. Sorby. 
bands rapidly disappeared, on account of the unaltered yellow 
chlorophyll being decomposed by sunlight far more rapidly than 
the product of the action of acids on blue chlorophyll.* 
Though a knowledge of this connection between fluorescence 
and absorption may thus often serve to indicate whether any 
coloured fluorescent solution is or is not a mixture, yet I must say 
that I do not think it furnishes conclusive evidence ; since I have 
found a few cases in which what appears to be a single substance 
gives a spectrum with two or more bright bands of fluorescence. 
The most decided case is that of the green colouring matter found 
in the annelid Bonellia viridis, described by me in a paper in the 
current number of the ' Quarterly Journal of Microscopical Science ' 
(April, 1875). This substance, which I have called honelleine, is 
green and has strong fluorescence, and the spectrum of the hght 
of fluorescence of a solution in alcohol shows two bright bands, — 
one red and the other green, — whose centres are at wave-lengths 
643 and 588, and their limits towards the blue end at 632 and 582, 
corresponding to two well-marked absorption bands, having their 
centres at 636 and 584, the latter being much less intense than the 
former. One might therefore suppose that it was a mixture, but 
on adding an acid the spectrum is materially changed, by the 
removal of some bands and the development of others, so that there 
is only one well-marked absorption band at wave-length 614, and 
a single red band of fluorescence, having the limit towards the blue 
end at 612, as though it were a single substance. Independent of 
the two bands of fluorescence, there is nothing to lead us to suppose 
that this colouring matter is a mixture. 
Similar facts are met with in the case of the product of the 
action of acids on blue chlorophyll, but the limit of the band of 
fluorescence in the green is a considerable distance towards the red 
end from the connected absorption band, which agrees with the 
general law, when, as in this case, the fluorescence related to the 
band in the green is comparatively weak. The yellow substance 
obtained from some Aphides, which I have named ajphidiluteine, 
gives fluorescence with three bright bands, as described in my 
paper in the ^ Quarterly Journal of Microscopical Science,' xi., 1871, 
p. 352. 
My conclusions therefore are, that though, on the average, the 
law adopted by Lubarsch is approximately correct, yet there are 
important differences in individual cases, depending on the relative 
intensity of the absorption and fluorescence, and in some instances 
it is necessary to modify the law very materially, so that it may 
express the connection between the fluorescence and more than one 
dominant absorption band. 
* ' Proccetlirigs of the Royal Society,' vol. xxi., p. 453. 
