152 
the isothermal curves obtained for different specimens, at 18°, with 
the cleavage plane normal to the field, are shown in Fig. 1. 
Attempts to identify the curves with such equations as 
On 
R, B, 
failed; it was found however that all the curves obtained at ordinary 
temperatures could, well within experimental errors, be represented 
by the formula 
EE ake Le aan 
Fr ats 
where &,, resistance at O° for = 0, 
R, 53 0 tors, 
lins de ,, O° in transverse field 5. 
A,n Constants. 
Owing to the difficulty of determining the dimensions of the 
specimens it is unfortunately impossible to give their absolute resistivity 
with any exactitude. 
From equation (1) we have, taking logarithms 
log fom! = log A + nlog 5 
Rh, 
which can be represented by a straight line, the coordinates being 
log (R’—R) R, and log 9. 
The values of Jog(R’—R) Rk, and log , corresponding to the 
curves shown in fig. 1, when plotted were found to lie on straight 
lines practically parallel to one another, indicating that is the 
same constant for each of these specimens. In the case of specimen 
G. 15 — the one which gave an increase of the greatest order — 
equation (1) did not hold as well as for the other specimens although 
the mean value of 2 was the same for this as for the others. 
. TAB LE ae 
NRG, nd 
Isothermals at 18° 
Specimen Ro | RR, = RIRo + An 
G. 4 0.0430 ohm. | 1.01 ++ 0.0171 191.145 
G.10 | 0.0792 , | 1.01 +-0.0205 w1.745 
G.11 | 0.0162 , | 1.004+ 0.0162 1.745 
G. 12 | 0.0430 , | 1.014 +0.0188 1.745 
G.15 | 0.0316 „ | 1.02 + 0.0214 mi.14 
