RECENT ADVANCES IN SCIENCE 385 



up the position that molecules as well as atoms of gases are 

 quite incapable of rotation. In place of rotation Kriiger sub- 

 stitutes precessional vibrations, the molecule being essentially 

 gyroscopic. These vibrations are totally distinct from the 

 " normal " vibration of two atoms along the line joining their 

 centres. Kriiger 's treatment deals with diatomic molecules of 

 the Rutherford-Bohr type, that is, a molecule consisting of two 

 atomic nuclei with two or more electrons rotating round the 

 line joining the atoms. As a result of collisions with other 

 molecules, Kriiger considers that these electrons may suffer 

 displacements and give rise to vibrations perpendicular to their 

 line of motion, with the result that the atoms themselves move 

 round in small orbits, i.e. the molecule possesses motion of the 

 precessional type. Kriiger points out that such motion is 

 entirely kinetic and involves two degrees of freedom, the cor- 

 responding energy term being RT, which is identical with that 

 postulated by Bjerrum on the basis of rotation. As far as 

 diatomic molecules are concerned, therefore, Kriiger 's view is as 

 capable of taking account of the molecular heats as is the view 

 of Bjerrum. Kriiger 's treatment possesses, however, the very 

 considerable advantage that it does not postulate atomic 

 rotations, whether the molecule be monatomic or not. Further, 

 Kriiger has shown that the precessional vibrations which 

 are to be ascribed to a monatomic molecule (argon) correspond 

 to frequencies so large that they need not be considered in con- 

 nection with molecular energy content and molecular heats. 

 In other words, we arrive at the logical conclusion that a mon- 

 atomic gas possesses translational energy alone. 



It may be mentioned that the precessional vibrations here 

 considered may be treated from the quantum standpoint, just 

 as the " normal " vibrations of the atoms may be treated. That 

 is, the energy content, in virtue of precessional vibrations, 

 decreases with falling temperature, and converges to zero as the 

 temperature reaches zero absolute. Kriiger has also shown 

 that the vibration frequencies involved in precessional motion 

 lie in the further infra-red region, at about 30 fi in the case of 

 hydrogen, and that the so-called rotation spectrum (Bjerrum, 

 Nernst Festschrift, 191 2) is really due to precessional vibrations. 

 Bjerrum, it may be remarked, ascribes the principal lines in the 

 short infra-red spectrum (X less than 10 fi) to the " normal " 

 vibrations of the atoms along their line of junction. This con- 



