10 Prof. E. C. C. Baly on 



frequencies. In order for it to gain a molecular quantum 

 at one of its true molecular frequencies, it will now only 

 be necessary for it to absorb the molecular quantum less 

 the atomic quantum already absorbed. It lias already been 

 shown how on the present conception summation of atomic 

 quanta can take place to form molecular quanta ; so it 

 would follow that, after the absorption of a given number 

 of elementary quanta beyond that associated with the 

 radiant equilibrium, the molecule will be able to absorb 

 the balance necessary to form one molecular quantum. 

 In other words, the molecules will be endowed with the 

 frequencies M — «A. 



Emphasis may be laid on the fact that under normal 

 conditions when the molecule is in radiant equilibrium 

 with its surroundings the subsidiary frequencies M + wA 

 are actually observed, and, further, that in these series of 

 subsidiary frequencies tiie maximum observed value of n 

 is one less than the critical value — that is to say, the 

 subsidiary frequencies associated with two consecutive 

 values of the molecular frequency do not overlap. Ob- 

 viously, if the molecule is screened from all external 

 radiation with frequency equal to its atomic frequencies — 

 that is to say, it is cooled to low temperatures — the whole 

 of the above deductions as to subsidiary frequencies fail, 

 and the subsidiary frequencies must therefore vanish. This 

 also has been observed, since at very low temperatures only 

 the central molecular frequencies remain. 



In the foregoing the simplest case only was dealt with 

 of a binary molecule formed by the combination of atoms 

 of two different elements. Exactly the same conditions 

 will, of course, obtain in more complex molecules, but added 

 to these will be new conditions resulting from the existence 

 of groups of atoms within the molecule. For instance, even 

 in the apparently simple case of the water molecule the con- 

 ditions will be more complex, owing to the undoubted fact 

 that in this molecule the hydroxy 1 (OH) group exists as an 

 integral portion of the molecule. Whilst, of course, the true 

 molecular frequency will be the convergence frequency of 

 all the atomic frequencies, it is the subsidiary frequencies 

 that will exhibit a greater complexity. This complexity, 

 however, is only one of degree, and its explanation follows 

 exactly the same principles as were laid down for the 

 simplest possible binary molecule. The specific case of 

 the water molecule may be discussed in which there are 

 three atomic frequencies: 1'0635 x 10 11 , 2'1159 X 10 11 , and 

 2*4531 xlO 11 . Whilst the true molecular frequency of the 



