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CAPTAIN ABNEY AND LIEUTENANT-COLONEL EE STING 
an absorption at 740, and a characteristic band one edge of which is at 892, and the 
other at 920. If we find a body containing the 740 absorption and a band with, the most 
refrangible edge commencing at 892, or with the least refrangible edge terminating at 
920, we may be pretty sure that we have an ethyl radical present. So with any of the 
aromatic group; the crucial line is at 867. If that line be connected with a band we may 
feel certain that some derivative of benzine is present. The benzyl group show this 
remarkably well, since we see that phenyl is present, as is also methyl. It will be 
advantageous if the spectra of ammonia, benzine, aniline, and dimethyl aniline be com¬ 
pared, when the remarkable coincidences will at once become apparent, as also the 
different weighting of the molecule. The spectrum of nitro-benzine is also worth com¬ 
paring with benzine and nitric acid. We should have liked to have said more 
regarding the detection of the different radicals, but it might seem presumptuous on 
our part to lay clowm any general law on the results of the comparatively few com¬ 
pounds which we have examined. In our own minds there lingers no doubt as to the 
easy detection of any radical which we have examined, but it will require more energy 
and ability than we possess to thoroughly classify all the different modifications which 
may arise. 
We may say, however, it seems highly probable by this delicate mode of analysis 
that the hypothetical position of any hydrogen which is replaced may be identified, a 
point which is of prime importance in organic chemistry. 
The detection of the presence of chlorine or bromine or iodine in a compound is at 
present undecided, and it may well be that we may have to look for its effects in a 
different part of the spectrum. The only trace we can find at present is in ethyl 
bromide, in which the radical band, about 900, is curtailed in one wing. The 
difference between amyl iodide and amyl bromide is not sufficiently marked to be of any 
value. We quit this part of our subject in the hope that chemists will be able to help 
us to decipher more than has as yet been done. 
Solar coincidences. 
We have already stated that in order to determine the wave-lengths of the 
absorptions in the different spectra, we have taken photographs of the solar spectrum 
on the same plate with that of a few of the principal substances. Unfortunately, 
when at first we took up the iodides we had no opportunity of thus obtaining 
a direct comparison between the Fraunhofer lines and ethyl iodide; but as a 
matter immediately affecting our results this has nothing to do, since all the sub¬ 
stances mapped are mapped in reference to ethyl iodide. When our maps were at 
the point of completion, and in fact when all the measurements but two or three 
had been made, it struck us that we might find some analogy between the solar spec¬ 
trum of this region and our linear absorptions, since these are presumably due 
to hydrogen. At that time we noted several of what appeared to be coincidences 
