154 
MR. H. TOMLINSON ON THE INFLUENCE OF STRESS 
The B.C. was now taken off and the direct action of the magnetizing coil on the 
galvanometer was found to produce a deflection of 8'00 + . Therefore there seemed 
to be an increase of resistance caused by magnetization represented by 2'23 scale 
divisions. The B.C. was again put on, and by taking out and putting in - 1 ohm 
several times it was ascertained that this caused a movement of the image of the 
wire through 74'0 divisions. Moreover, when the M.C. was flowing, putting in or 
taking out '1 ohm caused the same effect, and therefore the M.C. did not affect the 
sensibility of the galvanometer. In this case * 1 represented an alteration of resistance 
amounting to '001 per unit, and therefore the increase of resistance from inagnetiza- 
2 - 23 x - 001 
tion would be -■ -per unit= ’000031 per unit and ‘0031 per cent. 
74 
The B.C. was now reversed and the following observations taken : — 
umber of trial. 
Deflection of galvanometer- 
needle in scale-divisions. 
+ signifies apparent increase. 
— signifies apparent decrease. 
1 
7-50- 
2 
8 -00- 
3 
8 -00- 
4 
775- 
5 
775- 
0 
8-25- 
Mean 
7'88- 
The B.C. was again taken off and the direct action of the coil on the galvanometer 
appeared to be now 9\5 —Here, therefore, there would be an increase of resistance 
equal to that represented by 1 '62 scale divisions, and the amount of increase would be 
'0022 per cent. Again, the resistances of 100 ohms on two sides of the bridge were 
replaced by 10 ohms, so that now the arrangement having become more sensitive, a set 
of observations similar to the above gave an increase of resistance equal to 3'88 divisions 
of the scale, corresponding to an increase of '0029 per cent. From the three sets of 
observations it was concluded that the electrical resistance of bismuth is increased by 
longitudinal magnetization by '0027 per cent, for the amount of magnetizing force here 
employed. The increase per unit of resistance for a unit magnetizing force would be 
21 X10“ 8 . 
* For some reason the direct action of the magnetizing coil on the galvanometer was never quite the 
same for both directions of the M.C. 
