AND STRAIN ON THE ACTION OF PHYSICAL FORCES. 
67 
clamp C connects the metal to be tested with a similar strip, and both strips with 
one terminal of the galvanometer; whilst the clamps A and B serve, as before, to 
connect the strips with the resistance coils and battery. 
Fig- 12. 
The strip to be examined was strained by means of a stout wooden lever, and the 
table which supported the upper hooked iron rod was surrounded with baize. 
Expei •imei 1 1 X VI. 
A strip of iron foil, 10 centims. in length, 2'1 centims. in width, and of specific 
gravity 7'65, was subjected to a stress of 120 kilogs., and after two or three applications 
and removals of this load, it was found that this stress produced a diminution of 
resistance which required the sliding piece to be shifted through 20 divisions of the 
platino-iridium wire, and that on the removal of the stress the resistance was in¬ 
creased by the same amount. The load was distributed over a sectional area of '098 
square centim., and the diminution of resistance, which would be caused by a stress of 
1 grm. per square centimetre, was calculated to be 123'6X 10 -13 per unit. Inasmuch, 
however, as only one-third of the total resistance measured was effected by the stress, it 
was assumed that if the whole of the piece could have been strained to the same extent 
the diminution would have been 37lXl0“ B ; whereas in the case of iron wire sub¬ 
jected to longitudinal traction the alteration of resistance produced by the same stress 
amounted to 2111 X 10 -13 , or nearly six times as much as that caused by transverse 
traction. Again, if we assume that the value of “ Young’s modulus ” is the same for 
the foil as for the wire, the total alteration of resistance caused by the transverse 
K 2 
