148 
Physics. — “The effect of temperature and transverse magnetisation 
on the resistance of graphite.’ By Davw E. Roserts. (Com- 
municated by Prof. H. HE. J. G. pv Bors). 
The investigations of GRUNMACH and Werpert’), PATTERSON?) and 
others on the effect of transverse magnetisation on electrical resistance 
show that paramagnetic and diamagnetic metals exhibit an increase 
of resistance when magnetised, while the three ferromagnetic metals, 
at least in sufficiently strong transverse fields, show a decrease. 
Although as yet no simple relation may be given between the order 
of magnitude of this effect and the corresponding magnetic suscep- 
ibility, it may be noticed that the effect increases in the ratio of 
one to a hundred as we pass from paramagnetic tantalium to dia- 
magnetic cadmium and suddenly again a thousandfold as we pass on 
to bismuth. This element, as is well known, possesses rather a high 
diamagnetic specifie susceptibility (— 1,40.10—-6). Soon after Morris 
Owen *) found Ceylon graphite to show the highest value yet observed, 
Dr. W. J. pr Haas was led, by analogy, to anticipate that graphite 
might exhibit a variation of resistance of an even higher order when 
magnetised and suggested to me to search for the effect. The 
preliminary experiments *) performed with powdered graphite pressed 
into a thin plate, with irregularly shaped pieces and with ordinary 
pencils amply satisfied expectation and justified an extended investi- 
gation of the phenomenon. 
Well defined crystals of graphite are exceedingly rare and could 
not be procured ; the ordinary material occurs in lamellar agglome- 
rations, cleavable with great ease along surfaces parallel to the base 
of the hexagonal system. From a chemical point of view the structure 
is possibly very complicated; graphite is generally considered, above 
372°, the most stable of the three allotropic carbon modifications. 
The conductivity for heat of this substance has lately been studied 
by KoenicsBERGER and Wuiss®). The resistivity as formerly determined 
by several observers ®) is as follows: 
1) L. Grunmacr and F. Weipert, Ann. der Phys. 22 p. 141, 1907. 
2) J. Parrerson, Phil. Mag. (6) 3 p. 643, 1902. 
3) Morris Owen, Versi. Afd. Natuurk. 20 p. 673, 1911. Ann. der Physik. 37 
p. 657, 1912, 
4) When magnetised transversely in a field of 20 kilogauss, the compressed 
powdered Ceylon graphite gave an increase in resistance of 52 °/); an irregularly 
shaped piece gave 219°/); HB and 5B pencils by A. W. Fazer gave only 30/0 
increase, 
5) J. Korntnasperger and J. Werss, Ann. der Physik. 35 p. 27, 1911. Verh. d. 
Deutsch. physik. Ges. 14 p. 9, 1912. 
6) See Handb. der Anorg. Chemie 3 (2 Abtl.) p. 54, 1909, 
