138 
MR. H. TOMLINSON ON THE INFLUENCE OF STRESS 
The wire passed over a large wooden pulley, P, and to the other end of it was attached 
a scale-pan for holding weights. The light clamps «, b, c, having been well secured to 
the wire, were connected up in the usual manner, as shown in the figure, with the 
galvanometer, battery and resistance-coils, the connecting wires in this case being for a 
distance of 2 feet of rather fine silk-covered copper, in order to avoid the strain which 
would probably have ensued from the comparatively heavy caoutchouc-covered wires 
ordinarily employed. The whole arrangement was then carefully covered over with 
baize, and water allowed to trickle from a small cistern through S, S for about an hour, 
the space B having been previously filled with water. After a sufficient time had 
elapsed to render the parts of the wire of the same temperature, the effects on the 
resistance of magnetism alone or magnetism combined with strain were determined. 
The tangent galvanometer was placed in the circuit of the coil A* for the purpose of 
measuring the current passing through the coil. 
Experiment LIX. 
An annealed iron wire, ‘093 centim. in diameter. B.C. produced by one Leclanche. 
M.C.+ by 10 Grove cells with adjustable resistances in the external part of the 
circuit. 
Number of kilogs. 
or. the wire, scale-pan 
weighing 2 kilogs. 
not included. 
Tangent of deflection 
galvanometer 
= tan a. 
Alteration of resistance 
in terms of the 
platinum-silver wire = d ; 
one division = an alteration 
of '00081 per cent. 
d 
tan a 
0 
123 
48-6 
395 
0 
•249 
65-0 
261 
8 
•249 
40-0 
0 
•105 
40'0 
381 
4 
■105 
270 
6 
•105 
22-0 
Experiment LX. 
Another piece of the same wire was loaded and unloaded several times with a 
weight of 1 2 kilogs., and was afterwards allowed to rest for several days unloaded. 
The changes of resistance were then determined by noting the position of the light on 
the scale, the B.C. being produced by a large Daniell’s cell, the circuit of which, as 
well as that of the galvanometer, was kept closed as soon as the balance had been 
* In the figure the manner in which the compound strand of the coil is arranged in “series” is not 
shown. 
f The current in the circuit of the “Wheatstone’s bridge” will be denoted by B.C. and that in the 
magnetizing circuit by M.C. 
