due to (he Scattering of Light by Electrons, 733 



A.ain, the geometrical asymmetry which is necessary for 

 rotation will depend on the distances of: these electrons from 

 the carbon atom. Thus, to predict the rotation produced by 

 a molecule containing one un symmetrical carbon atom and 

 represented by OR] R 2 R 3 R 4 , we require to know the pro- 

 perties of the linkages 0R l5 CR 2 , CR 3 , 0R 4 ; i. e., we require 

 to know the frequency of the coupling electron in the linkage 

 CB and its distance from C. 



Unfortunately our knowledge on these points is extremely 

 meagre. We might expect to get some knowledge of the 

 frequencies by mapping the absorption spectra of various 

 hydrocarbons-. Thus, if the coupling ( VH had a frequency n l5 

 we might expect to find in the absorption spectrum of a 

 compound containing this coupling a band corresponding 

 to this frequency, modified it might be by the proximity of 

 other couplings in the molecule. A study of the spectra of 

 compounds containing the coupling O-OH might, in a 

 similar way, lead to the knowledge of the frequency of the 

 electrons concerned in this coupling. And in this wa} r , by 

 the study of the absorption spectra of a large number of 

 organic compounds, we might hope to determine the fre- 

 quency of the coupling of the carbon atom with the various 

 atoms and radicles to which it is joined in organic compounds. 

 < Jonsiderable progress has been made in the study of such 

 absorption spectra. Thus Hartley (see Kayser's "Spectro- 

 scopy/ vol. iii.), working with ultra-violet light down 

 to the- wave-length 2000, studied the absorption in the ultra- 

 violet down to this limit, and discovered well-defined 

 absorption bands in benzene and other aromatic compounds 

 containing! the benzene ring-. Our knowledge of this subject 

 has been greatly extended by Stark and his collaborators 

 who, by using fluorite lenses and prisms, were able to" work 

 with ultra-violet light down to wave-length 1850, and dis- 

 covered, among other things, bands which they ascribed to the 

 linkages = and = 0. AVe are however not yet, I think, 

 in a position to be able to say what are the fundamental 

 frequencies of the various linkages ; to do so we require 

 observations over a wider range of frequencies extending to 

 wave-lengths considerably smaller than those hitherto studied, 

 for in thi-, the Schummn region, nearly all gases have great 

 absorption, and some of it may well be selective. The 

 experiments hitherto made indicate that the frequencies 

 corresponding to the linkages O-H and C-OH will be very 

 far in the ultra-violet, and consequently larger than the 

 normal value. Now, on the view we have taken, a high 

 frequency corresponds to a large effective mass, so that in 



