520 



Physics. — ''Farther experiments with liquid heUurii xV. \AMA.-ejfect 

 and the change of resistance in a inaynetlc jiehi X. Measure- 

 ments on cadmium, graphite, gold, silver, bismuth, lead, tin 

 and nickel, at hydrogen- and helium-temperatures. By Prof. 

 H. Kamerlingh Onnes and K. Hof. (Communication N". 142/'; 

 from the Physical Laboratoiy at Leiden.) 



(Communicated in the meeting of June 27, 1914). 



§> 1. Method. The method was the same as that used in the 

 measurements of this series by H. Kamerlingh Onnes and Beckmann 

 (cf. Comm. N°. 129a and others). The notation is also the same as in 

 the previous papers. As regards the HALL-efFect, we used both the 

 method in which a galvanometer-detlection caused by the effect is 

 read and the compensation-method, in view of the fact, tliat the 

 latter, although in general to be preferred, as it allows the elimination 

 of various disturbances, is very troublesome, wlien small effects 

 have to be measured. The differential-galvanometer used was of the 

 KELViN-pattei-n with a volt-sensibility of 5 X 10~^ ; it was iron shielded 

 and was mounted according to Julius. As to the resistance measure- 

 ments these were partly performed in immediate connection with 

 the determination of the HALL-effect, in which case the resistance 

 of the plate used for this purpose was at the same time measured, 

 partly (by means of the compensation-apparatus) with wires which 

 were wound on thin sheets of mica and could be placed either at 

 right angles to the field or parallel to it, the latter specially w^ith 

 a view to investigating the considerable difference between the trans- 

 verse and the longitudinal effect, which difference develops specially 

 at helium-temperatures. 



^ 2. Bismuth. In accordance with frequent practice (e.g. by 

 Kamerlingh Onnes and Beckmann) we used this substance in the 

 form of pressed plates. The peculiarities in the resistance observed 

 by Streintz with conductors of compressed powder — although 

 occurring also in our plates at higher temperatures — were Tiot 

 observable, when the plates were cooled below 0° C. 



The plates which served for our investigation were pressed in a 

 steel mould and heated to about 200° C. in an electric furnace. 

 When made in this way the granular structure was still clearly 

 observable with a magnifying glass. The plate Bivi was made 

 without special precautions ; with plate Biyn the metallic powder 



