151 
EXPERIMENTS AT ORDINARY TEMPERATURE [18°]. 
About twenty specimens of Ceylon graphite were investigated, 
which all gave variations of resistance of a nigh order, the increase 
of resistance in a field of 20 kilogauss varying however between 
300 and 500°/, of the resistance in zero field. Considering the 
difficulty, of obtaining specimens of graphite of definite crystalline 
structure and having regard to the impurities occurring in the natural 
substance these variations in the magnitude of the effect are not 
surprizing. About five specimens, which gave a variation of resistance 
of greatest order were investigated more particularly; by analogy 
with the well-known behaviour of more or less pure bismuth‘) the 
assumption appeared justifiable that these were more likely to be 
pure and perhaps of more uniform crystalline structure. Some of the 
specimens were supported free between thin mica or glass plates; 
when imbedded in sodium silicate, collodion or Canada balsam allowed 
afterwards to solidify they did not experience any change in the 
magnitude of their increase of resistance in the magnetic field, thus 
eliminating any doubts that the effects were due to bodily strains 
in the graphite. In the final experiments at different temperatures 
the graphite pieces were supported by fine flexible wires between 
thin mica plates so as to avoid any strain due to possible expansion 
or contraction. The specimens could be mounted with their connections 
so that the total thickness amounted to less than 0.7 mm, thus 
enabling them to be examined in fields up to 50 kilogauss. Some of 
R ip ISOTHERMAL CURVES. 8-/8* 
J TRANSVERSE MAGNETISATION, 
R = Hesitranee at 0 Ho 
Re. 1. 
1) EF. C. Brake, Ann. der Physik 28 p. 449 1909. 
