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Physics. — “On the Hatt effect and the change in the resistance 
in a magnetic field at low temperatures. 1. Measurements on 
the Haut-effect and the change in the resistance of metals and 
alloys in a magnetic pield at the boiling point of hydrogen 
and at lower temperatures’. By H. KAMERLINGH Onnes and 
Benet BECKMAN. Communication N°. 1292 from the Physical 
Laboratory at Leiden. . 
(Communicated in the meeting of June 29, 1912). 
§ 1. Introduction. An investigation of the Harr effect and of the 
change of resistance produced by a magnetic field was carried out 
by van EVERDINGEN at Leiden some time ago down to liquid air tem- 
peratures *), but the fundamental importance of these phenomena in the 
theory of electrical conduction has long made it desirable to extend 
this investigation to the much lower temperatures which have been 
freely available since the successful development of methods of 
obtaining accurate series of observations at liquid hydrogen tempe- 
ratures. The problem, however, has been forced aside by other 
researches which could not be delayed, until the study of it and of 
allied problems for various metals at the lowest possible temperatures 
has been rendered essential to the further development of the theory 
of electrons by the discovery of the fact that the resistance of 
pure mercury disappears at liquid helium temperatures. We have 
therefore been occupied for some time with various aspects of 
the investigation of these problems at hydrogen temperatures, and, 
while we propose to continue this investigation systematically and, 
if possible, to make some measurements on the more important points 
at those temperatures which are obtainable with liquid helium, we give 
in the present paper some results which have already been obtained, 
and which may be considered to be themselves of some importance. 
The investigation has been extended by one of us (B. BECKMAN) 
with the same experimental material to temperatures obtainable with 
liquid ethylene, liquid oxygen, and liquid nitrogen, and these results 
will be discussed in a later paper. 
We wish to record our heartiest thanks to Mrs. A. Buckman for 
her assistance in the course of the measurements. 
1) The results for bismuth (and antimony) given in’ the dissertations of LEBRET 
(Leiden 1895) and vAN EVERDINGEN (Leiden 1897) and in Communications Nos. 19, 
26, 37, 40, 53, 58, 61 have been confirmed by BLAKE, Ann. d. Physik. 28, 449, 
1909 and Lownps, Ann. d. Physik 9, 677, 1902. Lownps investigated rods cut 
in different directions from bismuth crystals, and extended his investigation for one 
direction down to liquid air temperatures. He found that with the crystalline axis 
perpendicular to the field the Hat coefficient is negative at higher temperatures, 
while as the temperature is lowered it vanishes and then becomes positive, 
