
Coeficient of Kxpansion of Pure Nickel. 627 
nexion by a Committee of the British Association in 1890 *. 
With these anomalous changes has also been associated the 
phenomenon of recalescence ; “but it is noticeable, as Tomlinson 
has pointed out, that recalescence only appears in specimens 
for which the “untwist” is delayed in the manner just 
described. Thus in Tomlinson’s view, iron possesses two 
critical points in respect to torsional rigidity, the lower one 
at a dull red heat, at which recalescence occurs (if at all) and 
at which the intensity of the magnetization vanishes ; and 
the other at bright redness, w ith which is associated the 
elasticity change ‘for both rising and falling temperatures in 
the case of soft i iron, and for a rising temperature only in the 
case of harder specimens. 
Tomlinson observed the same effect for an impure nickel 
(containing a large percentage of iron), but he failed to 
observe any such changes in the pure metal. 
Up to the present time the same remark has generally been 
believed to apply to Gore’s phenomenon for nickel. 
he experiments described below were made with the object 
of testing this last point rather more carefully, since a change 
in the coefficient of expansion at or near the magnetic critical 
point was certainly probable, in view of the resemblance of 
nickel to iron as regards peculiarities in their physical 
properties. 
The nickel employed was from a very pure specimen of 
wire, kindly given to the author some years ago by Professor 
Pech. Callendar, F.R.S., and which has been already used in a 
research on the temper ature variation of thermoelectric force 
and resistance, as well as in an investigation (shortly to be 
published) on the magnetic properties of nickel at high 
temperatures. 
The diameter of the specimen was 0:0765 em. 
Present Huperiments. 
The method employed in the present experiments was to 
observe by means of reading-microscopes the expansion of a 
definite portion of the nickel wire. The wire was heated 
electrically by direct passage of a current through it, and its 
temperature was deduced trom its resistance. “The relation 
between temperature and resistance had previously been 
determined by experiments on the same specimen of nickel +. 
* B. A. Report, 1890, by Committee on “ Molecular Phenomena 
associated with the Magnetization of Iron.” 
+ Harrison, Phil. Mag. February 1902. 
202 
