146 MR. H. TOMLINSON" ON THE INFLUENCE OE STRESS 
the third and fourth values* of -, which may perhaps be assumed to represent approxi¬ 
mately the average alteration of resistance for a given moderate magnetizing force, we 
find that with this wire the increase per unit of resistance produced by an absolute 
electromagnetic unit of magnetizing force would be 2335 X 10 -8 . 
It is desirable to draw attention also to the fact that with both iron and nickel there 
is no change of resistance of the nature of a decrease produced by magnetization, but 
that starting with a current from one Grove’s cell through a total external resistance 
of about 15 ohmst and with a magnetizing force not greater than 26 times the earth’s 
horizontal magnetic force at the place, we find a continuous increase of resistance as 
the magnetizing force is increased. 
The Effect of altering the Strength of the B.C. on the Change of 
Resistance produced by any Magnetizing Force. 
The results recorded in the last two experiments are so far at variance with 
Auerbach’s views already alluded to, that it seemed advisable to still further test 
these views by altering the strength of the B.C. whilst that of the M.C. is maintained 
constant. 
Experiment LXIV. 
A piece of the same annealed nickel wire as that used in Experiment LXI. was 
tested with one Grove’s cell and a total external resistance of 15 ohms for the M.C., 
and with from one to three Grove’s cells with no external resistance save that offered 
by the “ bridge ” and its connexions for the B.C. 
Deflection of the needle of the 
tangent galvanometer, showing 
the strength of the B.C. 
Increase of resistance caused 
by the magnetization in terms 
of the divisions of the 
iridio-platinum wire. 
12 
101 
15 
10-3 
m 
10-9 
The numbers given in the second column are the means of several observations, and 
agree very fairly with each other, the difference between them being within the errors 
of observation, and what difference there is would show that we have a slightly 
greater increase of resistance for large values of the B.C. than for small ones. 
* The first two values of - are not included, for the reason pi’eviously mentioned. 
a 
| That is, 10 olims in addition to the resistance of the coil and its connecting wires. 
