149 
Graphite from Ceylon at O° | 12.10-* ohm per cm° 
- »» Siberia Aas Vr Ort Hee ohne Atte hg 
% »~ Greenland „15° LOA are Ny leg, 
The best of my samples gave a resistivity as small as 0,5.10-4, 
i.e. roughly about half that of mercury (0,96.10-+ at 18°): this z- 
creased with rise of temperature by about 0,001 per degree. The 
resistivity of amorphous carbon has always been found to be much 
larger and is well-known to decrease with rise of temperature; the 
coefficient diminishes, however, as the transformation into the graphitic 
modification proceeds'), although it has never been observed to 
change its sign. 
With regard to the effect of magnetisation Parrmrson l.c. found 
the resistance of a glow-lamp filament to increase by 0,027 percent 
in a transverse field of 25 kilogauss. According to Cray *) the resis- 
tivity of such a filament decreases by 24°/, on heating from — 255° 
to O°. Laws *) has investigated the effect for transverse magnetisation 
of glow-lamp filaments, pencils and graphite without finding it to 
be of a high order. He found, at ordinary temperatures, the increase 
of resistance of the graphite in a field of 11 kilogauss to be about 
1°/, of the resistance when outside the field, while at the temperature 
of liquid air the effect was increased threefold. Within this small 
range the increase of resistance was found proportional to the square 
of the field and between the temperatures 18° and —186° inversely 
proportional to the absolute temperature. As will be seen these results 
are not in agreement with those found in the present research. 
EXPERIMENTAL ARRANGEMENT. z 
The specimens most used in this investigation were prepared from 
the same Ceylon graphite as that used by Owen in his researches 
on its thermo-magnetic properties; a chemical analysis has not yet 
been made. Short rectangular pieces (7—10 mm. long, 1—2 mm. 
wide and 0,1—0,5 mm. thick) were obtained by careful cleavage 
and those -selected for investigation which appeared of most pro- 
nounced and uniform crystalline structure. For the determination of 
the effect of transverse magnetisation they were, in general, supported 
in the magnetic field so that the cleavage planes were perpendicular 
to the field i.e. the erystallie axis was parallel to the lines of force. 
On supporting the pieces freely in a magnetic field it was observed 
1) See Handb der Physik 4 p. 380, 1905. G. Wr…epemanN, Elektrizität, 1 p. 539, 
1882. 
2) J. Cray. Dissert., Leiden 1908. 
3) S. GC. Laws, Phil. Mag. (6) 19, p. 694, 1910; his graphite was obtained from 
the Morean Crucible Co., London. 
