66 
MR, H. TOMLINSON ON THE INFLUENCE OF STRESS 
Experiment XV. 
A piece of carbon rod, 4 inches in length and ‘1386 square centim. in section, was 
compressed by putting a weight of 2 kilogs. on to the pan at the end of the lever. 
Number of trial. 
Alteration of resistance 
as represented by 
the number of divisions of 
the platino-iridium wire 
through which it was 
necessary to move the 
sliding-piece in order to 
balance the effect of 
putting on or taking off 
2 kilogs. 
1 
118'0 
2 
118-5 
3 
iio-o 
4 
115-5 
Mean 
115-4 
From the results of Experiment XY. it was calculated that a compression of 1 grm. 
per square centimetre would cause a decrease of resistance of 6398 X 10 -13 per unit, 
and as the longitudinal elasticity was 267‘2 X10°, the alteration of resistance 
attending an amount of compression which would suffice to halve the length of the 
rod would be 1-710, and of this alteration ’210 would be in the specific resistance of 
the rod. The specific resistance of the specimen at 15° C. was 4214 X 10 -6 . 
We see that the effect of compression is to diminish both the total resistance and 
the specific resistance of the specimen of carbon, and is therefore of an opposite 
nature to that of longitudinal extension. 
The Alteration of Electrical Conductivity produced by Stress applied 
in a direction Transverse to that of the Current. 
It has been seen that, in the case of most metals, stress applied in the same direc¬ 
tion as that of the current increases, both permanently and temporarily, the resistance, 
and it seemed probable that stress when applied in a direction perpendicular to that 
of the current would alter the resistance in the opposite direction. The following 
arrangements were therefore made with the view of testing this point:— 
Strips of metal foil about 10 centims. long, 2 centims. broad, and ’01 centim. thick, 
were arranged in pairs as in fig. 12. D and E are stout brass clamps into which two 
hooked iron rods are screwed, and the strip to be examined is clamped into the brass 
pieces, which are 8 centims. in length, but insulated from them by means of silk. The 
