5OF: BARON VON WREDE ON THE ABSORPTION OF LIGHT. 
lation were compared with the distance between two consecutive mi- 
nima instead of with the differences between the representing lengths 
of undulation, which would presuppose that the refrangibility ofa colour 
would be proportional to its length of undulation, this can be consi- 
dered as proving nothing more than that the reasoning and the expe- 
riment coincide in showing that the’ absorptions in the green colour lie 
closer to one another than in the red. 
I must finally remark that, although I have considered the retarda- 
tions only as arising from reflection between the particles, I also easily 
conceive the possibility that this idea may be incorrect, and that all the 
retardations may arise from causes as yet quite unknown to us. But | 
think I have shown by what I have stated that the phenomena of ab- 
sorption may be reduced to a simple mathematical principle; and that 
these phenomena, as belonging properly to the absorbing bodies, point 
to certain determined magnitudes, which can be given in an absolute 
measure, and the closer examination of which, whatsoever their cause 
may be, must always be highly interesting. 
