155 
being in position, this reverse current was set up and the resistance 
of the graphite found. The temperature of the graphite was then 
deduced from the temperature curve ( = 0) fig. 2. Owing to the 
difficulty of exactly getting rid of the residual field without setting 
np a field in the opposite direction, and on account of the small 
change of resistance with temperature, this method of determining 
the temperature does not seem to be susceptible of great accuracy. 
The isothermals at low and high temperatures were determined for 
G11 and G15. Except for the difference in the magnitude of the 
changes of resistance concerned similar results were found. The 
results obtained with specimen G15 are shown as isothermal curves 
(fig. 3) from which the so-called isopedie curves (J) = constant) may 
Tsomegmaeueves, GIS 
Tran sve nse, LTA GNETISATION. 
Fig. 3. 
easily be deduced. As will be seen, the increase of resistance is 
much greater at low temperatures. At the temperature of liquid air 
the increase is 93800 °/, for a field of 38,8 kgs, the increase at 18° 
being 1250 °/,. | 
The isothermal curves for the lower temperatures cannot be re- 
presented by an equation of the form (1); at higher temperatures 
this seems to- be the case, although more accurate measurements 
appear desirable. 
41 
Proceedings Royal Acad. Amsterdam. Vol. XV. 
