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CAPTAIN- ABNEY AND LIEUTENANT-COLONEL BESTING 
In conclusion, we have to say that we are indebted to Dr. Frankland, Dr. Arm¬ 
strong, Dr. Russell, and Dr. Guthrie for several organic substances ; but to 
Dr. Hodgkinson are our thanks especially due for the ready manner in which he lent 
us many choice specimens of his own preparation, and for the kind advice he was at 
all times ready to offer us (and which we freely accepted) as to the kind of compound 
to examine which would most aid us at any particular stage of our research. It is 
almost superfluous to mention that our work has been largely aided in the preparation 
of photographic material by Sergeant Jackson, R.E., and we take this opportunity of 
thanking him for the least interesting portion of the work which he so willingly 
carried out for us. The labour may be appreciated when it is considered that many 
hundreds of photographs have been taken, some 300 of which have been measured and 
compared. A research of this kind is always arduous, but it has been lightened by 
the cordial cooperation of those whom we have named. Our thanks are also due to 
Mr. Dick for the careful way in which he has drawn our maps. 
Appendix. 
The following appendix contains a tabular statement" of all the lines and bands 
measured in the different compounds mapped ; where not otherwise expressly stated, 
6 inches was the length of the column of liquid used. 
The intensities of the lines have been taken as 1 , f, and ^ : the first-named 
intensity signifying total transparency in the photographs. When an intensity is 
shown as ^ ^ J j it means that there is a gradually increasing intensity of absorption 
between the first-named edge of a band and the centre of it, and that it decreases at 
an equal rate on the other side of the centre to the second-named edge of the 
band. When a band is shown as of one intensity (say J), it means that the whole of 
that band has an equal intensity throughout. When it is shown as (say) 0 to 1 it 
means that the intensity increases from 0 at the first edge of the band and terminates 
abruptly at the second edge. These explanations, it is believed, will suffice to make 
the appendix clear. The sources from whence the substances analysed were obtained 
are shown in the tables. 
* The approximate wave-lengths have been added since the paper was x’ead, March, 1881. 
