the Rotation- Energy of Molecules. 



79 



Bjerrum found, too. that the water-vapour bands between 

 10 and 20 //, determined by Rubens and Aschkinass* (Table II. 

 eol. 3) form such an arithmetical progression, and he assumed, 

 therefore, that these bands also are caused directly by the 

 molecules' rotation. 



Fig. 4. 



1600 



1700 



But on referring to the curve in fig. 2, or to the values 

 calculated from this curve in Table II. (cols. 1 and 2), we find 

 at once that a simple arithmetical progression is out of the 

 question. The positions of the determined maxima seem to 

 be very irregularly distributed. A. Bucken f, however, has 

 attempted to arrange these calculated values in two arith- 

 metical progressions, of which the one is a continuation of 

 the above-mentioned series with a constant frequency- 

 difference A = l'73xl0 12 , and the other a series with the 

 difference 0*75 x 10 12 . According to Eucken these two series 

 may be explained by the lack of symmetry of the molecules, 

 which, he says, may result in the rotation-energy's being 

 divided between two chief moments of inertia. 



* Rubens u. Aschkinass, Wied. Ann. lxiv. p. 584 (1898). 

 t A. Eucken, Verh. d, D.p/ujs. Ges. xv. p. 1159 (1913). 



