AND STRAIN ON THE ACTION OF PHYSICAL FORCES. 
129 
cooling liad been allowed, that the elasticity of both iron and steel is temporarily 
diminished by raising the temperature to 100° C. 
From Wertheim’s researches* we gather that in the case of iron and steel there is 
the following increase of elasticity between 15° to 20° C. and 100° C. 
Table XXIV. 
Metal. 
Increase per cent, of 
elasticity between 
15° to 20° and 100° C. 
Annealed iron .... ... 
4-90 
Annealed iron wire. 
6-91 
Annealed cast steel. 
279 
Annealed English steel wire . 
23-20 
Steel tempered blue. 
518 
The increase of elasticity of the steel wire seemed so remarkable that it was deter¬ 
mined to retry Wertheim’s experiments by direct observations of extension, using the 
same scale and vernier as have been already described in Part I., and placing the 
wire and the comparison-wire in the same air chamber as had been used in measuring 
the alteration of resistance produced by loading at different temperatures. The length 
of wire between the clamp, which rested on a wooden support on the top of the 
chamber, and tire vernier was 4 feet 4 inches, and of this length 2 inches or rather 
more would be, roughly speaking, at the temperature of the room when the rest of the 
wire w T as heated by steam to 100° C. We must therefore multiply any observed effect 
on the elasticity caused by raising the temperature of the wire to 100° C. by a number 
which is about 4 per cent, of the apparent alteration. The air chamber rested 
(fig. 18) on a piece of wood, A A, 8 inches long, 6 inches broad, and ^ inch thick, and 
this in turn on two stout bricks, B B, which were supported by a wooden table, D D. 
The wire to be examined, X, and the comparison-wire, Y, were, as usual, secured at one 
end of each to the same clamp, C, which rested on a piece of hard wood, E E, placed 
at the top of the chamber. The wires, X and Y, passed through two small holes made 
in E E, and also through a hole in the table, and to their lower ends were attached, in 
the one case, a scale-pan, and in the other a cross-bar of wood, H H, carrying constant 
equal weights. Exactly the same precautions were taken as have been already 
fully described in Part I., and, as in experiments on the alteration of resistance pro¬ 
duced by loading, the air chamber was well covered with baize and paper. 
Under these circumstances it was possible to maintain a very constant temperature 
of 100° C., and even had the temperature varied slightly it wall be seen that no 
appreciable error would have been introduced, as the variation would have altered 
the lengths of X and Y to the same extent. 
* Ann. de Cliimie et de Phys., 3 me serie, 1844, p. 431. 
MDCCCLXXXIII. 
S 
