( '2 ) 



exceedingly narrow on one end, that we could not expect much 

 effect of the insolation on the corresponding parts of the negative, 

 even if diffraction were to be excluded from before hand. 



I do by no means intend to say that by what precedes the con- 

 clusion might be justified, that X-rays are diffracted and that they 

 have a icave-length of about 0.1 a 0.2 /li /u. Yet, as we have arrived 

 through two or three independent ways at results which agree pretty 

 well, those results — though each of them, the first excepted, may 

 separately be of nearly no value at all — if taken together make 

 me believe, that the conclusion mentioned may possibly be not very 

 far from truth. Moreover they make a fuither investigation in the 

 same direction desirable. A.s to the result mentioned under 1°. I 

 think it may be accepted without any restriction '). 



Physics. — The galvanornaynetic and thermomaynetlc phenomena in 

 bismuth^ by Dr. E. van Everdingen Ju. [Communication 

 No. 42 from the Physical Laboratory at Leiden, by Prof. 

 H. Kamerlingh Onnes). 



In order to explain the galvanomagnetic and therraomagnetic 

 phenomena Riecke ^) assumes that a galvanic current is always 

 accompanied by a current of heat, and a current of heat by a gal- 

 vanic current. The basis of these hypotheses lies in Weber's theory 

 of the conduction of electricity and heat in metals; in tliis theory 

 also the conduction of heat is ascribed to the motion of charged 

 particles alone. 



The velocities of the positive and negative particles are : 

 for a slope of potential of 1 C. Gr. S. unit per cM. u and — o 

 for a slope of temperature of 1° per cM. gp and (?„. 



In the magnetic field // a positive ion with the velocity U is 

 acted upon by a force B U for each unit of electricity. 



KiECKE assumes further that the velocities in the direction of this 

 force of the particles aie zero in the state of equilibrium in the case 

 of the phenomenon of Hall ; the equilibrium is reached by the 

 combined action of a difference of potential and of temperature 

 between the sides of the plate. 



In this way he finds for the coefficient of the galvanomagnetic 



1) With great pleasure I acknowledo-e tlie assistance given by Mr. C. Sctioute in 

 the measurements, necessary for the experiments. 

 -) (iüilt. Niichr. 1898. 



