148 
MR. H. TOMLINSON ON THE INFLUENCE OF STRESS 
Experim ent LX VII. 
A strand of four pieces of the same length and of the same steel as that used in 
the last experiment was tested with one Grove’s cell in the B.C., and seven in the 
M.C., and the alteration of resistance, which, however, could not be accurately 
measured, was certainly not greater than that of the single wire when the same 
battery-power was employed for both the M.C. and the B.C. The change of resistance 
of the compound strand under the above-mentioned conditions was measured at 
•040 per cent, with a probable error of 25 per cent. 
The Effect of Longitudinal Magnetization on the Electrical Resistance 
of a Bar of Steel. 
As my earliest investigations recorded in the previously-mentioned “ Preliminary 
Notice ” had seemed to show that the alteration of the electrical resistance of iron and 
steel which can be produced by magnetization is very much greater, for the same 
amount of magnetizing force, when the metals are in the form of comparatively thick 
rods than in that of wires, the following experiment was made. 
Experiment LXVIII. 
A steel knitting-needle, taken in the ordinary condition, 23 centims. in length and 
•233 centim. in diameter, was provided with two copper terminals, 14 centims. in 
length and '410 centim. in diameter, holes having been bored 1^ centim. in depth at 
one end of each terminal so as to admit the ends of the needle. A similar and 
similarly-furnished needle served as the comparison-piece, and the two were connected 
with each other and with the other parts of the “ bridge ” in the same manner as the 
wires in the last experiments had been. The clamps used, however, were more 
massive and the whole of the steel to be magnetized was well within the coil A, 
whilst the comparison-piece was outside the coil and at right angles to it. The 
amount of magnetism induced was measured as before, but the resistance introduced 
into the circuit of the galvanometer employed for this purpose had to be made very 
considerably greater than was the case with the iron wire, in order that the “ throw ” 
of the needle might be reduced to the proper extent. The B.C. was produced by four 
Grove’s cells, and the M.C. by seven Grove’s cells, each with adjustable external 
resistance. The following are the results obtained :— 
