2S2 



Mr. H. Tomlinson. The Influence of f Jan. 26, 



knowledge concerning elasticity, had examined the elasticity of iron 

 and steel after these metals, tested at the higher temperature of 

 100° C, had again cooled down to the lower one, he would have found 

 that what to him appeared, in the case of these metals* to be a tem- 

 porary increase of elasticity was really a permanent one, and if the 

 wires used had been tested several times, first at the higher and then 

 at the lower temperature, he would have also found, provided sufficient 

 rest after cooling had been allowed, that the elasticity of both iron and 

 steel is temporarily diminished by raising the temperature to 100° C. 



ISTot only is a comparatively large and permanent change produced 

 in the elasticity of iron by merely raising the temperature to 100° C, 

 but in the case of well annealed iron wire there is sometimes an enor- 

 mous change produced in the ductility (in one specimen the ductility 

 was diminished 50 per cent.) by the same process ; and since very 

 appreciable effects have been proved to be brought about in the same 

 manner in the magnetic inductive capacity, the specific resistance, 

 and the thermo-electrical properties of iron and steel, it would appear 

 that researches on these properties might lend valuable aid in investi- 

 gations on the liability of wrought-iron axles to fracture, which is 

 produced by sudden changes of the temperature of the air. 



It was further noted that shortly after the iron or steel has been 

 heated and then cooled, there is less elasticity than when a rest of 

 some hours has been allowed, and in fact we have in the case exactly 

 the same kind of restitution of elasticity as we have seen takes place 

 after a wire has received mechanical extension. With nickel the 

 increase of elasticity produced by rest after cooling is still more 

 remarkable. 



The effects of very slight mechanical strain, and of the strain 

 caused by raising annealed iron or steel to 100° C, and afterwards cool- 

 ing, on the torsional rigidity of these metals were next examined, and 

 it was shown that the torsional rigidity is affected in a precisely similar 

 manner to the longitudinal elasticity, both by raising the temperature 

 to 100° C, and then cooling, and by the strain resulting from slight 

 mechanical traction. On the whole it was seen that as regards either 

 purely mechanical strain, or that caused by tempering, there are for 

 iron and steel three critical points : very slight strain increasing, 

 moderate strain diminishing, and excessive strain again increasing 

 both the torsional and longitudinal elasticity. 



The temporary alteration of susceptibility to change of resistance 

 from change of stress, which is effected in the case of nickel by 

 raising the temperature to 100° C, is as remarkable as the suscepti- 

 bility itself, and the maximum diminution of resistance which could 

 be produced by stress when the metal was at the temperature of the 

 room was actually more than twice that at 100° C. 



* " Ann. de Ckimie et de Phys.," 3me serie, 1844, p. 431. 



