
[i s62 6°44] 
LXX. On the Temperature-Variation of the Coefficient of 
Expansion of Pure Nickel. By HE. Puitip Harrison, 
PhD. (Ziirich), 1851 Exhibition Research Scholar of Uni- 
versity College, London; King’s College, Cambridge*. 
le 1869 G. Goret published an account of some experi- 
ments .on “A Momentary Molecular Change in Iron 
Wire,” in which he showed that if a stretched iron wire be 
heated io bright redness and then allowed to cool, at a certain 
temperature there occurs a diminution in the rate of con- 
traction of the metal, which may even become a momentary 
expansion in the case of particular specimens under suitable 
conditions. It was found that three conditions were necessary 
in order to obtain this effect, which is generally known as 
‘*Gore’s Phenomenon.” 
(i.) The wire should be cooling. | 
Gi.) It should be under a sufficient tension. 
(iii.) It should have been heated to a sufficiently high 
temperature. 
In every case observed by Gore, the wires after use were 
tound to be permanently elongated. 
Some years after Gore’s experiments Barrett t showed that 
this anomalous behaviour of iron was not confined to cooling 
specimens alone, but that the effects occur just as definitely, 
though in the reverse order, when the wire is heated. 
A phenomenon similar to that of Gore was noticed by 
‘H. Tomlinson § during a research on the torsional rigidity of 
iron wire at high temperatures. He found that if the spe- 
cimen were heated while under the influence of a very small 
torsional couple at bright redness, there occurred a sudden 
twist in the wire in the opposite sense to the applied couple, 
while an “untwist” took place at the same temperature 
during cooling. ‘The effect is as though there were a sudden 
increase in the elasticity of the iron at a certain temperature 
during heating. For soft iron, this twisting jerk occurs at 
approximately the same temperature whether the metal is 
heated or cooled; but for hard specimens the twist is delayed 
during cooling till a lower temperature is reached. 
These sudden changes have long been regarded as having 
connexion with the loss of magnetic quality which occurs in 
iron at a high temperature, and were considered in this con- 
* Communicated by Prof. J. J. Thomson, F.R.S. 
+ G. Gore, Proc. Roy. Soc. 1869. 
t Barrett, Phil. Mag. ser. 4, vol. xlvi. 
§ Tomlinson, Phil. Mag. vol. xxiv. (1887). 
