649 
Physics. — “On the Hatt effect, and the change in resistance in 
a magnetic field at low temperatures. ILI. Measurements at 
temperatures between ae C. and —200° C. of the Hat 
effect, and of the change in the resistance of metals and alloys 
in a magnetic gield”. By Beret Beckman. (Communicated by 
Prof. H. KAMERLINGH ONNEs). Communication No. 180a from the 
Physical Laboratory of Leiden. 
(Communicated in the meeting of September 28, 1912). 
§ 1. Introduction. A communication was made by KAMERLINGH 
Onnes and the present writer to the meeting of June 29th 1912, of 
the results of measurements of the Harr-effect and of the increase 
of resistance in a magnetic field made by us at liquid hydrogen tem- 
peratures. In the present paper those results are extended to the tem- 
peratures which are obtainable with liquid ethylene and liquid 
oxygen, with the same experimental material and following the same 
experimental methods. It is of great importance that observations made 
with any particular substance should be distributed as uniformly as 
possible over the region of temperature under investigation. The 
measurements now completed make it possible for the results obtained 
at liquid hydrogen temperatures to be compared with those of former 
experimenters, who, without exception, proceed only to liquid air 
temperatures. 
For a description of methods and material we may refer to the 
above Communication N°. 129a. In order to complete the diagrams of the 
present paper the results for liquid hydrogen temperatures in the 
paper quoted are also indicated without making specific mention of 
the fact on each occasion. The present paper is confined to a discus- 
sicn of the results obtained with bismuth. 
’ 
I. Bismuth. 
§ 2. Change in the resistance of a wire of electrolytic bismuth. The 
resistance of the bismuth wire Btj7 was measured in eight different 
fields at five different temperatures: 7 — 290° K, 170° K, 139°.5 
K, 90° K, 72? K. These results are given in Table I. A is the field 
strength in gauss, aw’; the resistance in ohms in the magnetic field 
at the absolute temperature 7’, wy the resistance without field at that 
temperature, and w, the resistance without field at 0° C. 
Fig. 1 shows the increase of resistance as a function of the field 
at constant temperature (Isotherms), and fig. 2 the increase of resis- 
tance as a function of the temperature under constant field (Isopedals). 
