1912-13.] Electrical Resistance and Magnetization of Nickel. 203 
Hence 
p dN _ dxy _ 
Q(M.~ dC~ S ’ 
a ratio given immediately by the experimental readings. 
But initially, since C is small, the balanced Wheatston e-bridge ratio 
holds to a sufficient approximation, namely, 
P/Q = M/N ; 
and hence finally we have the very simple relation 
dN/N = -*ZM/M, 
where everything on the right-hand side is known. If now n is the resist- 
ance of the nickel which forms part of the conductor whose resistance is N, 
the change dn is the same as dN, and the change in unit resistance is to 
be calculated from the expression 
dn_N dN_ = _ N dM 
n n N n M 
In the present experiments the resistance of N was 0*0478 and that of the 
nickel strip 0*0378, giving the ratio N In equal to the reciprocal of 0*791. 
As the experiments were carried out, the deflections were obtained by 
reversing the steady current through the system. The following two sets 
of numbers, taken just as they were jotted down in the laboratory book, 
will show how the observations were made and so far reduced : — 
Experiment of June 6, 1906. Calibration Experiment. 
Shunt. 
Readings. 
00 . 
. 131 131-9 
83-5 84 
50 . 
. 101 101-3 
114-1 114-5 
00 . 
. 131*2® 
83-8/ 
Deflection 
= 30-1 30-2 
30*4 30-6 
= •955 
The first reading 131 is obtained with positive current without the 
shunt resistance in connection. The shunt 50 is then introduced, and the 
reading changes to 101. The shunt is thrown out, and the reading 
becomes 131 2. It is put in again, and the galvanometer reads 101*3 
(passing up the second column). Finally, with the shunt thrown out, the 
reading is 131*9. The current is then reversed and an exactly similar set 
of readings are taken. These appear in the fourth and fifth columns, the 
fifth being read up as in the case of the third. The fourth row of figures 
gives the deflections, each of which is the difference of the “ shunt ” reading 
and the mean of the “ non-shunt ” readings which precede and follow. The 
sum of these four deflections is taken and divided by the reducing factor 
