( 473 ) 



on one side, he gets in first approximation the same result as I had 

 obtained from the beginning. But only in first approximation. 



All this is the cause that I still prefer the simple direct deduc- 

 tion of the pressiire, as I have given it. (Proc. of the meeting Nov. 

 1898) — even though there remain questions whose solution I have 

 tried to find already for some time, but in which I have not yet 

 succeeded. 



Physics. — n^he galvano-magnetic and thermo-maf/netic phenomena 

 in bismuth." (Second communication continued). By Dr. E. 

 VAN EvERDiKGEN Jr. (Communication N°. 48 (continued) 

 from the Physical Laboratory at Leiden, by Prof. H. Kamer- 

 LINGH Onnes). 



6. In § 6 of my first communication on this subject ^) I men- 

 tioned that in my opinion Riecke wrongly ascribes the entire con- 

 duction of heat to the motion of charged particles, and that for the 

 theory we might perhaps derive some profit from such suppositions 

 as I have introduced in the theory of the HALL-eftect in electro- 

 lytes. ^) It certainly is remarkable, that, starting from the supposition, 

 that the current of heat in metals is a pure current of energy, 7iot 

 accompanied by a current of ponderable substance, we for all trans- 

 verse galvano-magnetic and thermo-magnetic phenomena can offer 

 at least a qualitative explanation. For, we have only to represent 

 the matter in the following way: 



In the electric current the positive and negative charged particles, 

 which for the sake of brevity we shall call ions, move with different 

 velocities, while also their numbers may differ. 



In the magnetic field the electro-magnetic force causes transverse 

 displacements and consequently charges which increase until the 

 currents of positive and negative electricity have reached the same 

 value. This equalisation may be due to the arising difference of 

 potential (this is the HxLL-effect) as well as to currents of diffusion 

 of the ions. (If the latter are accompanied by a perceptible difference in 

 the number of ions per unit of volume in different places, the diffe- 

 rence of potential to be observed at the HALL-electrodes might be 



') Proceedings Koyal Acad. Amsterdam June 25tli 1898 p. 72. Comm. Pliys. Lab. 

 Leideu N". 42 p. IS. 



2) rroceedings Koyal Acad. Amsterdam May 2Stli 18ÜS p. 27. Comm. Phys. Lab. 

 Leideu N". 41. 



