72 
MR. H. TOMLINSON ON THE INFLUENCE OF STRESS 
ends of the wire were soldered, were connected in the same way as before with C, C 
and the other parts of the bridge. The whole arrangement of wires and cylinders was 
placed in a wooden box having holes cut in one of the sides to admit of the connexions 
C, C and D, D passing through, and this box was in turn placed inside a larger one, 
so that the space between the two boxes could be filled with sawdust. 
The mode of proceeding was as follows :—-First, ice broken into small pieces w 7 as 
packed into a layer about 3 inches thick round the larger of the two cylinders, then, 
after an interval of about half-an-hour, both the large cylinder and B were filled with 
pounded ice, the cover put on, and over it placed a large sheet of paper containing 
sawdust. The tube E served to form by means of indiarubber tubing connexion with 
the air-pump, and after a sufficient time had been allowed to make the balance of the 
two wires constant the experiments began. 
This plan seemed to act admirably. A short time after exhausting the air there 
seemed to be an increase of resistance, and on letting' in the air again a decrease. 
After each operation with the air-pump the wires were tested at intervals of 10 
minutes, until it was certain that the full effect on the resistance of the alteration of 
the pressure had been produced. Each experiment lasted more than one hour, and it 
was only possible to make two or three experiments before the ice had to be readjusted 
round the wires ; as evidently after some three hours, though there might be no 
appreciable melting of the ice, the galvanometer showed that one or other of the wires 
was not quite at the temperature of the ice. The following are the results obtained:— 
Experiment XIX. 
Alteration of resistance 
represented by the number 
of divisions through 
| which it was necessary to 
move the sliding- 
I piece in order to restore 
the balance. 
Alteration of pressure 
in millimetres of mercury. 
1235 
700 
13-28 
721 
13-00 
730 
12-40 
718 
13-20 
710 
12-44 
707 
13'4G 
707 
1244 
707 
12-84 
708 
12-64 
708 
11-32 
708 
13-76 
708 
12-74 
707 
12-74 
707 
12-74 
707 
12-74 
710 
