108 
MR. H. TOMLINSON ON THE INFLUENCE OF STRESS 
Experiment XXXVIII. 
A wire of annealed copper, 3 feet in length and '095 centim. in diameter, twisted. 
Number of complete 
revolutions of torsion 
= A. 
Decrease of specific 
gravity per cent. 
= B. 
Ratio of B : A. 
400 
116 
•0029 
600 
1-66 
•0028 
800 
2T3 
•0027 
In Table XVIII. will be found the extent of change in the specific gravity of the 
different metals produced by a given amount of stretching, hammering, and twisting. 
Table XVIII. 
Name of metal. 
Percentage alteration of 
specific gravity attending a 
permanent increase of 
length of 1 per cent, 
produced by stretching. 
Percentage alteration of 
specific gravity attending a 
permanent increase of 
length of 1 per cent, 
produced by hammering. 
+ signifies increase of 
specific gravity. 
Percentage alteration of 
specific gravity attending a 
permanent torsion equal to 
that of 1 complete revolution 
in a length of 1 centim. 
+ signifies increase of 
specific gravity. 
Platinum .... 
-•0620 
German-silver . 
-•0612 
-•0136 
Nickel .... 
-•0510 
Zinc. 
-•0509 
-•0146 
-•01212 
Iron. 
-•0203 
-•0215 
-■00283 
Silver .... 
-•0156 
Aluminium . 
-•0082 
-•0183 
Copper .... 
-•0178 
+ •0065 
-■00252 
Platinum-silver 
+ •0159 
+ •00190 
In the last table a — sign signifies a decrease and a -f- sign an increase of specific 
gravity. 
The specific gravity of all the annealed metals here examined is decreased by 
permanent extension.* 
Hammering also decreased the specific gravity of all the metals subjected to this 
process except copper and platinum-silver; with these metals the specific gravity was 
slightly increased. 
Permanent torsion decreased the specific gravity of copper, zinc, and iron, and 
increased that of platinum-silver. 
Of the three processes, torsion produced the greatest maximum change in the 
specific gravity, thus it will be seen from Experiment XXXVIII. that the specific 
* This appai’ently is not always the case, as Sir W. Thomson mentions in his article on “ Elasticity,” 
‘ Brit. Encyc.,’ p. 1, that a certain specimen of: copper wire annealed in hot sand had its density increased 
more than 1 per cent, by longitudinal extension. 
