of Hydrogen and some other Gases. 307 



molecule, it may change with temperature, or by the change 

 of states, etc. ; and hence the observed susceptibility ^ may 

 change in a similar way, as actually observed. The con- 

 tinuous change of the susceptibility-atomic weight curve 

 from the paramagnetic elements to diamagnetic above 

 referred to is also explained on the same basis. 



According to the above theory, the molecules of a para- 

 magnetic substance must therefore possess a definite magnetic 

 moment, while those of a diamagnetic substance have only 

 a small magnetic moment or none. In Bohr's model of a 

 hydrogen molecule, v is decidedly greater than ^*, and 

 therefore % or X P + Xd * s positive i n contradiction to the 

 observed fact. 



In a recent paper, Professors Honda and Okubo f proposed 

 a new theory of magnetization of the gases. According to 

 the kinetic theory of gases, besides translational motions, 

 • the molecules of a gas are continuously making rotational 

 motions about their centres of mass ; and in their theory, 

 these molecules are treated as gyroscopes. Since the axis of 

 rotation of the molecules does not in general coincide with 

 the magnetic axis, the magnetic moment of the molecules is 

 supposed to be resolved in the direction of the axis of 

 rotation and that perpendicular to it. Under the action of 

 a magnetic field, the paramagnetic polarization results from 

 the former component and the diamagnetic polarization 

 from the latter, and therefore a resultant polarization is the 

 sum of these two. The resultant may be positive or negative, 

 according as 



paramagnetic polarization ^ diamagnetic polarization. 



The theory proves that the sign of the magnetization of a 

 gas depends on the shape of the molecules, and not in the 

 least on their magnetic moment. In fact, a gas whose 

 molecules have a definite magnetic moment comparable with 

 those of iron may be diamagnetic, provided the axis of 

 rotation is perpendicular to the magnetic axis. This kind 

 of diamagnetism is not dealt with in any of the previous 

 theories. In order to test these theories it is necessary to 

 have the correct values of susceptibility of different gases, 

 which are at present scarcely known. 



One of the chief difficulties which we encounter in the 

 determination of the magnetic susceptibility of gases, lies in 

 the preparation of pure gases, i. e. those which are perfectly 



* J. Kunz, Phys. Rev. xii. p. 59 (1918). 



t K. Honda and J. Okubo, Sci. Rep. vii. p. 141 (1918) ; Phys. Rev. 

 viii. p. "6 (1919). 



X2 



