PHYSICS IN 1913 617 



in general, the physical properties of the elements at low 

 temperatures are inadequately accounted for by present theories. 



The quantum theory has recently received a rather more 

 direct confirmation than is afforded by the work on the radiation 

 formula or the specific heats. Bjerrum put forward a new 

 conception of the mechanism of the absorption of radiations 

 in the infra red region. The charged atoms in the molecule, 

 which are the resonators accounting for the absorption, are 

 supposed not only to execute linear vibrations of frequency v u 

 but also to rotate with a frequency of rotation v.,. If they 

 vibrate in a direction normal to the axis of rotation there are 

 resultant vibrations of frequency v x -^-v^ v x — v 2 ; if along the axis 

 of rotation, the movements are independent. There will thus 

 result the four frequencies v u v 2} v v + v 2 , v x — v % . This will give 

 three periods in the short infra red and one in the long infra 

 red. Supposing the rotation frequencies continuously dis- 

 tributed according to the Maxwell probability law, this would 

 give three near absorption bands in the shorter infra red for 

 a gas, and Burmeister found experimentally that the absorption 

 in this part of the spectrum always occurred in broad double 

 bands, the midway absorption line predicted by the theory 

 being too narrow to detect. Now on the quantum theory the 

 rotation frequencies are not continuously distributed, but in- 

 crease in jumps ; according to this the double absorption bands 

 should not be smooth, but show a serrated edge, the series 

 of maxima corresponding to a series of separate absorption 

 frequencies. E. von Bahr has, by increasing the resolving 

 power of the infra red spectroscope used, actually found a 

 series of jagged irregularities in the absorption bands, of the 

 kind predicted by the theory indicated. This furnishes striking 

 evidence for the physical existence of quanta of energy, at any 

 rate in some cases. Eucken has further pointed out that the 

 measurements of the infra red absorption spectrum of water 

 vapour present exactly the irregularities required by Bjerrum's 

 theory if the rotational energy is distributed in quanta. The 

 band in the longer infra red has likewise been experimentally 

 found. 



In the matter of the specific heats at low temperature 

 Dewar's latest results are of considerable interest. He has 

 measured the mean atomic heat over a range of 6o° C. for 

 fifty-five elements at 50° absolute (the temperature fall being 



