892 
CAPTAIN ABNEY AND LIEUTENANT-COLONEL BESTING 
Substances examined. 
We append a list of substances the absorption spectra of which we have mapped on 
an empiric scale reduced to wave-lengths subsequent to the reading of the paper, but it 
must not be inferred that these are all that we have examined. There are various 
aqueous solutions which we have not dealt with in this paper, preferring to eliminate 
as far as possible any matter which did not seem to bear directly on the objects we had 
in view. We have, in addition to the map, made a tabular statement of each spectrum, 
inserting approximate wave-lengths, which we trust will be of use to future observers. 
Different hinds of absorption . 
It may be useful to state the different kinds of absorption with which we have met. 
1st. General absorption from the least refrangible end. 
2nd. Special absorptions 
’ Lines 
< 
_ Bands 
f fuzzy, or 
L sharp. 
rboth edges sharply defined. 
< one edge sharply defined. 
I both edges not sharply defined. 
Regarding the general absorption we have nothing very noteworthy to remark, 
beyond the fact that as a rule in the hydrocarbons of the same series those of heavier 
molecular constitution seem to have less than those of lighter. 
In regard to the special absorptions we may say that it is very often easy to distin¬ 
guish the position of lines at the edges of bands, though they are not sufficiently 
marked to be represented on the map. This is more noteworthy, when we have a 
change from a very dense absorption to a feebler one. The impression left on the 
mind is that in reality these particular bands are made up of lines of different 
intensities, but of this we cannot speak with authority. 
As to the possibility of any of these special absorptions being due to the carbon 
vapour, &c., of the arc, it will, we think, be sufficient to state that, as we do not find 
any trace of them in photographs taken without a liquid in front of the slit, we are 
quite satisfied that they can be due only to the substances with which we have 
experimented. 
Nature of the absorptions. 
As regards the nature of the absorptions caused by the different substances expe¬ 
rimented on, we started with no preconceived idea—we simply mapped what we 
measured. In our earlier photographs, which were of substances containing oxygen, 
we found the absorptions to be mostly in bands and irregularly-placed and ill-defined 
lines, the want of definition we now know being caused by maladjustment of the focus 
and a want of rigidity in our laboratory floor. It was not until we had removed our 
