﻿194: Mr. N. McCleland on the Absorption Spectra of 



mean that it is due to vibrations of the electrons o£ free 

 oxygen valencies alone, though these may contribute the 

 greater part of the effective absorbing power. Further, the 

 introduction of fresh vibration centres is bound to affect the 

 induction constants of those already present by altering the 

 relative positions of the orbits. These difficulties do not 

 greatly disturb the qualitative results, but introduce an 

 uncertainty into the values of the constants which can only 

 be overcome by accumulation of experimental results, espe- 

 cially in regions of the spectrum which have recently been 

 made available by Schumann. 



There are two kinds of motion possible for the electrons, 

 namely, in the plane of the orbit, and perpendicular to it. 

 There are also two kinds of absorption : the one is observed 

 in comparatively dilute solutions, very thin films or short 

 columns of vapour, the other 2 through considerable thick- 

 nesses of pure substance. It is likely that these two kinds 

 correspond to the two kinds of vibration. There are reasons 

 for thinking that the first kind, which alone is dealt with here, 

 depends on the vibrations in the plane. 



In the numerical part of the paper, since the data cover 

 only a small part of the spectrum it is impossible to obtain 

 sufficient equations to give all the unknowns. We are there- 

 fore obliged to make some assumptions as will appear. 



Rotation and Units. 



I represents coefficient of self-induction, or apparent mass, 

 m and sometimes/, g, </> of mutual induction, r the friction 

 of damping, c the stability. E# lp *is the disturbing periodic 

 force of the light. 



The unit of time is so chosen that when the wave-length 



is in fi/jb, p= - X 100. 



I is assumed to be the same for all electrons and is taken 

 as 1. 



m and c vary for different atoms, the former also depending 

 to some extent on the constitution of the molecule. 



For example, the mutual induction between two atoms is 

 increased when there is a mass of unsaturation outside them, 

 e, g. the mutual induction between the N= in MeN = N — Me 

 is less than that in the case of C 6 H 5 — N = N — C 6 H 5 . This is 

 readily explained as due to the repulsion of the unsaturated 

 electrons in the phenyl groups forcing those of the nitrogens 

 closer together. 



