40 
MR. H. TOMLINSON ON THE INFLUENCE OF STRESS 
rested upon a support of hard wood, D D, each, block being separated from its neigh¬ 
bours by wooden partitions. The block B was double the length of A and C, and into 
this was clamped one end of each of the wires, the other ends being clamped into A 
and C. A caoutchouc-coverecl copper wire connected a binding-screw on A with one 
Fig. 6. 
pole of a large- sized Leclanche and a similar wire, X, connected the same binding- 
screw with a set of resistance-coils (a, fig. 7). In a similar manner C was connected 
with the other pole of the Leclanche, and through Y with another set of resistance- 
coils, /3 ; whilst B, and the sliding-piece H, which traversed a wire, N N, made in the 
first instance of platinum-silver and afterwards of platino-iridium, uniting a and /3, 
were joined to two terminals of a reflecting galvanometer, G. The wire to be strained 
was provided with a movable pulley, S, 2 inches in diameter, to which was attached 
by means of a stout wire the scale-pan used in Part I., or, as in some experiments, a 
large pail weighing 4 kilogs. and capable of containing about 60 kilogs. of water; both 
wires were, before suspension, surrounded with caoutchouc-tubing silk or other insula¬ 
ting material. The aperture, B, could be closed by two wooden shutters, M M, having 
small semicircular holes cut in the centre of the extremities adjacent to each other, so 
as to leave only just sufficient room for the stout wire to swing freely; moreover, still 
further to prevent any errors which might be caused by chance currents of air, the 
top of the air-chamber was well covered with baize after the wires had been adjusted, 
and the table was also surrounded on three sides with a like material. 
