54 
MR, H. TOMLINSON ON THE INFLUENCE OF STRESS 
the length of the rod in metres, n the number of vibrations, A the density, and. E the 
elasticity in kilogrammes per square millimetre. 
In order to determine the alteration of resistance which could be produced by 
longitudinal traction, the rods were well coated for about 2 inches of their lengths 
with copper deposited by electrolysis, and were then arranged as shown in fig. 9. 
The rods passing through two holes in a table were secured at their upper ends by 
two clamps, A A, and at their lower extremities were fastened two other clamps, B B, 
either of which would also serve to carry a scale-pan suspended by an iron wire 
attached to its lower extremity. Two pieces of silk-covered copper wire, about 
6 inches in length and -^th of an inch in diameter, were soldered on to the deposited 
copper at E, and these being also joined together were connected with the galvano¬ 
meter. Two other pairs of similar wire were soldered at D, and one of each pair was 
connected, as usual, with the resistance coils, and the other with one pole of the 
battery. The resistances of the silk-covered copper wires at E, which were small 
compared with those of the rods themselves, were calculated by determining the 
resistance of some 6 feet of the wire, and assuming that the resistances of the short 
pieces at E and the actually determined resistance of the longer piece were 
proportional to their lengths. The whole table was surrounded on all sides except 
one with baize, and the mode of proceeding the same as usual. Experiment shows 
that with the loads employed the alteration of resistance is nearly proportional to 
the load. 
