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XXXI. The Effect of Change of Temperature in Twisting or 

 Untwisting Wires which have suffered Permanent Torsion. 

 By Herbert Tomlinson, B.A* 



IN a paper recently communicated to the Physical Society f , 

 Mr. R. H. M. Bosanquet has drawn attention to the 

 remarkable behaviour of a very fine hard-drawn platinum 

 wire, which twisted or untwisted very appreciably when sub- 

 jected to small variations of temperature. As some experi- 

 ments made by myself nearly eight years ago, but of which 

 the results have not been as yet published, seem to bear on 

 the interesting phenomenon in question, I now venture to 

 bring them forward. I had previously been investigating 

 the effects of permanent extension and compression on the 

 longitudinal elasticity of wires in the following manner: — 

 A wire of from 60 to 90 centimetres in length and 1 milli- 

 metre in diameter was suspended vertically, with its upper 

 extremity clamped to a rigid support, and its lower one attached 

 to a little brass block provided with a hook at the bottom, to 

 which weights could be attached. Permanent torsion was im- 

 parted to the wire, which was afterwards subjected to various 

 amounts of longitudinal stress. The permanent twisting of 

 the wire in the direction of a right-handed screw causes the 

 portion ABCD (fig. 1) to be permanently extended along the 

 diagonal AC and compressed along the diagonal BD (fig. 2). 

 Fig.]. 



If now the wire be loaded, the stress will produce tempo- 

 rary twist or untwist according as the elasticity is greater or 

 less in the direction B D than in the direction AC. A full 

 account of these experiments will be found in the ' Philoso- 

 phical Transactions' J, so that it will suffice to state here that 

 all the wires examined showed temporary twist or untwist to 

 be the result of loading. The amount of twist or untwist 



* Communicated by the Physical Society : read June 25, 1887. 

 t Phil. Mag. vol xxiv. No. 147, August 1887, p. 160. 

 X Part I. 1883 : "The Influence of Stress and Strain on the Physical 

 Properties of Matter." 



