( 2'? ) 



Physics. — „ On an asymmetry in the change of the spectral lines 

 of iron^ radiating in a magnetic field'\ By Dr. P. Zeeman. 

 (Will be published in the Proceedings of the next meeting). 



Physics. — The RkLh-effect in electrolytes. By Dr. E. van Ever- 

 DINGEN Jr. (Communication N°. 41 from the Physical Labo- 

 ratory at Leiden, by Prof. H. Kamerlingh Onnes). 



1. The researches on the HALL-effect and the increase of resist- 

 ance in the magnetic field for bismuth, communicated to the 

 Academy in the Meetings of 30 May 1896, 21 April and 26 June 

 1897 ^), and afterwards treated more at large in my dissertation, 

 induced me to put the question, whether these phenomena may 

 justify a choice among various theories about the nature of the 

 electric current and the resistance of metals. A first step towards 

 answering this question was the deduction of a formula for the 

 HALL-efFect in electrolytes, with the aid of simplifying suppositions. 

 Indeed it is generally assumed that in electrolytes the electric current 

 consists in a convection of charges by the ions; the velocities of 

 this motion are known in many cases, hence all the data for the 

 calculation are present. This research, already begun in Chapter 

 VIII of my dissertation, being concluded for the present, I wish 

 here briefly to communicate the results. 



2. Several phj'sicists have tried to observe the HALL-effect in 

 liquids. They succeeded indeed in observing differences of potential, 

 caused by a magnetic field in solutions of sulphate of zinc and 

 copper which were traversed by currents, and changing their signs 

 on the reversal of the magnetic field or of the current. Whereas 

 however in most metals the HALL-effect is proportional as well to 

 the strength of the current as to the field, and in all metals the 

 difference of potential appears immediately on closing the magnetizing 

 current, in the liquids this difference increases more tiian the current 

 and less than the magnetic field, and after the applying of the field 

 it grows slowly towards a maximum. Chiefly on account of the last 

 named fact RoiTi ^), Florio ^) and Chiavassa *) refused to acknow- 

 ledge the differences of potential observed also by themselves as 



') Commimicntions from the Pliys. linl). at the Univ. of Leiden. N". 26, 37 and lO. 

 a) Atti della E. Ace. dei Lineei 12 p 397, 1882; Journ. de Pliys. 1883. 

 ') II nuovo Cimeato, Ser. 4, Ï. 4, p. lUC, 189fi. 

 *) Elettricista 6, 1897. 



