1000 
gen temperatures at which FR, (Rk for H= 0) is about 5°/, greater 
than R for H = 10000. 
For both plates the Harreffect increases at lower temperatures, 
… Pook . ne 
while the ratio — is the same. This is very remarkable, for the 
2900K 
plates are completely different with regard to their specific resistance, 
resistance temperature coefficient and absolute magnitude of the 
Harreffect. For both plates the value of the Hatteffect is small 
compared with that obtained by A. v. ErriNGHauseN and W. Nernst’), 530, 
and also by H. Zann’), and the electrical conductivity is also small. 
According to the researches of A. Marrairsen’), F. Exner*),W. Haken’), J. 
F. Kroner’) and others, various modifications of tellurium occur; accord- 
ing to Kroner it exhibits dynamical allotropy. The two moditica- 
tions have very different conductivities. The specifie gravity of the 
plate Te,77 was 6.138; this is perhaps connected with the cireum- 
stance that it cooled slowly after casting, and that it was subjected 
to local heating when fusing in the electrodes. For a preparation 
very quickly cooled Kroner gives a specific gravity as low as 5.8. 
The modification with the lowest specific gravity seems to have the 
smallest electrical conductivity. 
§ 21. The Hatrefect in Bismuth crystals. In Table XIII, Comm. 
N°’. 1294, we gave results of measurements of the Harreffect in 
bismuth crystals for the case in which the erystalline axis is per- 
pendicular to the field, and the main current runs in the direction 
of the axis. To these we are now in a position to add results for 
the case in which the field is parallel, and the main current perpen- 
dicular, to the axis. For these measurements we used one of the 
erystal prisms which had been used by Vay EverpincEn (Suppl. No. 2) 
in his measurements, choosing the most regular of the three (2, 3 
and 5 1. ¢.) which bad been found suitable for this purpose (cf. p. 82 1. ¢.). 
In the following Table are given fk, H and RH in eg.s. 
At ordinary temperature and in weak fields AH is negative, as 
was first discovered by Van EVERDINGEN and subsequently confirmed 
by J. BECQUEREL ‘). 
1) A. von Errrn@HAUsEN und W. NerNsr. Sitz. Ber. Akad. d. Wiss. Wien. 94, 
. 560, 1886. 
2) H. ZAHN. Ann. d. Phys. 23, p. 146, 1907. 
5) A. MATTHIESEN und M. von Boss. Pogg. Ann. 115, 385, 1862. 
4) F. Exner. Sitz. Ber. Akad. d. Wiss. Wien. 73, 285, 1876. 
5) W. HAKEN. Inaug. diss. Berlin 1910. 
6) J. F. Kroner. Inaug. diss. Utrecht 1912. 
7) J. Becgueren, C. R. 154, p. 1795. June 24, 1912. 
— 
~ 
