8 Prof. E. C. C. Baly on 



true molecular frequency when the absorbing or radiating 

 power of molecules is examined at ordinary temperatures. 

 Two important points must be discussed : first, the forma- 

 tion of the subsidiary frequencies; and, second, the course 

 of events when a molecule absorbs energy at one of these 

 subsidiary frequencies. As regards the latter point, it 

 seems to have been assumed that the molecule as a whole 

 absorbs one energy quantum at that subsidiary frequency. 

 This assumption is very unsatisfactory, for the width of 

 an absorption-band group is often very great ; and hence 

 it becomes necessary at once to postulate the acceptance 

 of a molecular quantum which may vary between very 

 wide limits indeed on account of the great difference in 

 frequency between the extreme subsidiary frequencies in 

 a given absorption-band group. The variation necessary 

 in the size of the molecular assumption is impossibly great. 

 The conception of a molecular quantum given above defines 

 it at once as a quantum measured at one of the exact 

 multiples of the true molecular frequency, and on this 

 conception it is impossible for a molecule as a whole to 

 accept any quantity of energy which is greater or less 

 than one molecular quantum. 



These subsidiary frequencies have been attributed by 

 Bjerrum to the rotation of the molecules and by Kriiger * 

 to their precessional motions ; but, as hns been shown in 

 the preceding paper of this series, both these theories 

 break down. In the first place, neither theory takes 

 account of the fact that the subsidiary frequencies are 

 due to the atomic frequencies: and, in the second place, 

 it is necessary for the purposes of these theories to postulate 

 impossibly large variations in the values of the molecular 

 rotation or molecular precession. 



On the other hand, the conception now put forward of 

 elementary atomic quanta of energy, whereby definite 

 atomic frequencies are established, would seem capable of 

 affording a very simple and straightforward explanation. 

 Moreover, this conception leads to the establishment of 

 exact frequencies without any possibility of variation. 

 The case may again be considered of the molecule formed 

 by the combination of the two elementary atoms for 

 which the elementary quanta are 9 x 6*56 x 10~ 17 and 

 1*5 X 6*56 x 10~ 16 erg, and which therefore exhibit the cha- 

 racteristic frequencies 9 X 10 10 and 1*5 x 10 11 respectively. 

 Ex liypothesi the elementary quantum is associated with 

 the shift of one stationary orbit to another, and, of course, 



* Ann. der Physik, 1. p. 346, li. p. 450 (1916). 



