208 Transactions of the Royal Microscopical Society. 
7. Conclusion. 
Having only recently adopted the above-described wave-length 
system, I have not yet been able to apply it sufficiently to feel 
confident that the kind of general laws now briefly indicated 
are of universal application. Before any such conclusion would 
be justifiable, far more examples must be carefully studied, with 
apparatus specially designed for the investigation of the mutual 
relations of the absorption bands, and this inquiry must be accom- 
panied with appropriate chemical and physical experiments. This 
is what I propose to do, as soon as circumstances permit, since 
I feel that what is now known is little more than sufficient to indi- 
cate the line of research that ought to be followed, and to show 
that the wave-length method is incomparably better than any 
other. We can scarcely believe that spectra are not subject to 
definite laws ; and, though it may prove difficult to ascertain all 
these laws in terms of the most important physical character of the 
light of different parts of the spectrum, yet we may be certain that 
no such general relationships could be detected by discussing the 
measurements given by an arbitrary scale, the value of the divisions 
of which in different parts depends upon the irregular dispersion of 
the prisms, and have no simple and direct connection with any 
physical peculiarity of the light itself. 
Note . — The figures of spectra given in this paper being drawn 
in relation to wave-lengths, as if seen in an interference spectrum, 
the red end will appear to be abnormally expanded and the blue 
end contracted to anyone accustomed only to spectra seen in prism 
spectroscopes. 
