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Capt. W. de W. Abney. On the [Feb. 10, 



February 10, 1881. 



THE PRESIDENT in the Chair. 



The Presents received were laid on the table, and thanks ordered for 

 them. 



The Right Hon. Mountstuart Elphinstone Grant Duff was admitted 

 into the Society. 



The following Papers were read : — 



I. "On the Influence of the Molecular Grouping in Organic 

 Bodies on their Absorption in the Infra-red Region of the 

 Spectrum." By Captain W. de W. Abney, R.E., F.R.S., and 

 Lieutenant-Colonel Festixg, R.E. Received February 5, 

 1881. 



(Abstract.) 



The authors describe the apparatus used by them in their research 

 and their plan of mapping the absorption spectra, the results being- 

 given in wave-lengths. The source of light for obtaining a continuous 

 spectrum was the incandescent positive pole of an electric light, the 

 electricity being generated by an M. Gramme machine. The light 

 was passed through tubes containing the fluid, and the absorption 

 spectra photographed in the infra-red region. 



The absorptions they met with they class as follows :— 



1st. General absorption at the least refrangible end of the spectrum. 



J Fuzzy. 

 1 Sharp. 



rBoth edges sharply defined. 

 <^ One edge sharply defined. 

 LBoth edges less sharply defined. 



The authors next discuss the causes of the different absorptions met 

 with in various fluids. From experiment they show that a large 

 number of lines which are formed in hydrocarbons containing no 

 oxygen are common to substances containing hydrogen and no carbon, 

 and that in carbon tetrachloride and carbon disulphide, no lines or 

 bands are to be met with. By this eliminating process they deduce 

 the fact that the presence of lines is due to the hydrogen in the bodies. 



Lines . . 

 Bands . . 



