﻿Organic Substances and the Electron Theory. 195 



Bands are spoken of as on the near or remote side of one 

 another with reference to the red end of the spectrum. 



The data refer as far as possible to alcoholic solutions, 

 these being most abundant. 



I. One vibration centre only. 



This is the case developed by Drude 1 . 

 The fundamental equation of motion may be put in the 

 form 



Ix + rx + cx^e^ (i.) 



If we assume x=Xe ipt for steady motion, we find 



X(fy> 2 -^-6<) = -E . . . (ii.) 



giving X. The development of this is well known ; in par- 

 ticular it appears that the frequency of free vibration, 

 corresponding to that of the ray most strongly absorbed, and 

 so to the head of the band, is given by 



_Zp 2 -hc = ; (iii.) 



and also that the sharpness of the band depends on the 



9 



r c 



smallness of ~j- • 



The only substances belonging to this type that have been 

 examined are the aliphatic iodides 24 . The I vibration 

 centre gives rise to a band at about X 252. 



In what follows, the cases where there are several vibration 

 centres will be treated as follows : — 



First, the "frequency' 5 equation (corresponding to (iii-)) 

 will be investigated to find the positions of the heads of the 

 bands, then in a few cases the iC characteristic " equation 

 (corresponding to (ii.)) will be examined to determine their 

 nature. 



II. Two vibration centres. 

 The equations of motion are 



l{x + m{y + r v c + c v v = Ee 1 ?* | .. . 



mh' + Ijij + r 2 y + c, y = E &\ J 

 assuming the relation 



2 



