( ,S5() ) 



Inlliieiice oi" a licld of 40 Kilooauss. 



650.5 



651.3 



0.09 

 (some- 

 what 

 vague) 



0.09 

 (some- 

 what 

 vague) 



is widened; the width amounts to 0.35 mi, the 

 baud on the violet side is darker than the one lying 

 towards tlic red ; (possibly a quadruplet is formed, 

 which, however, is uncertain) ; a displacement, 

 however, was not observed. 



increases in width and fades away ; the width 

 amounts to 0.40 f//t ; a shift towards violet seems 

 to take j)lace, but could not be ascertained. 



§ 30. Seventh series. 



We now investigated. 



Uranyl potassium sulphate [_U0^ K^ ('^'^4)2 4~ "^ H^(J\ 



A ihombic plate containing both axes, 0.7 m.m. thick, was examined 

 i|i a held of about 40 kgs. with unpolarized light at — 193°. The 

 well-known bands appeared to be much more numerous and narrower 

 than for uranyl nitrate (c.f. §11), among others 487.8, 488.2,488.8 

 and 490.5 in the blue. These bands seemed to fade somewhat iji 

 the tield, but the phenomenon w^as uncertain here, and in any case 

 the widening did not amount to more than 0.02 mi. For the many 

 bands in the violet no action of the field could be perceived. 



Physics. — "The value 0/ the self-induction according to the electron- 

 theory." By Prof. J. D. van der Waai.s Jr. (Communicated by 

 Prof. J. D. VAN DER Waals\ 



Many physiciists refer to the existence of self-induciioji in order 

 to make the existence of kinetic energy of electrons more intelligible. 

 To a certain extent there is no objection to this, provided we keep 

 in \'\c\\, 1^^ that the kinetic energy consists for a large part 

 electrical energy whereas for the calculation of the self-induction 

 oidy the magnetical energy is taken into account, and 2'"' that from 

 a theoretical point of view it is the self-induction which is to be 

 explained from the kinetic energy of the electrons, and not vice- 

 versa. It is this second point which occasions me to make tlie 

 following remarks. 



Let us imagine a piece of metal which contains a great number 



