256 Mr. H. Tomlinson on raising Iron under Temporary 



unannealed piano-steel rise of temperature caused a very ap- 

 preciable temporary twist, instead of untwist, even with small 

 loads on. 



A remarkable feature about all these experiments was the 

 great difference with different metals in the facility with which 

 the effect of permanent torsion in one direction could be re- 

 versed by permanent torsion in the opposite direction. With 

 copper, for example, one complete revolution in the opposite 

 direction was sufficient to reverse the effect of 200 complete 

 turns of permanent torsion, whilst with iron the difficulty of 

 reversing the effect of previous torsion was considerable. 



I am inclined to believe that the phenomenon observed 

 by Mr. Bosanquet is to be, at any rate partly, attributed 

 to unequal expansion in different directions. I have always 

 found in wires which have been hard-drawn a certain amount, 

 and sometimes a considerable amount of permanent torsion : 

 this, we have seen, will cause temporary twist or untwist 

 to be produced by rise of temperature. The amount of twist 

 or untwist in any case, however, observed by myself was very 

 much less than that observed by Mr. Bosanquet; and it would 

 be of interest to ascertain- how far the comparatively very 

 large variation of torsion with small rise of temperature which 

 occurred with the platinum wire used by him, is to be attri- 

 buted to the comparatively great longitudinal stress on the 



XXXII. Remarkable Effect on raising Iron when under Tem- 

 porary Stress or Permanent Strain to a Bright-red Heat, 

 By Herbert Tomlinson, B.Aj\ 



IT has been shown in the preceding paper that an annealed 

 iron wire which has been permanently twisted is tempo- 

 rarily untwisted when the temperature is raised to 100° C, pro- 

 vided there is not too great a load on the end of the wire ; but 

 that if the load on the end of the wire is sufficiently great, a 

 temporary twist follows on the rise of temperature. Fresh 

 experiments were therefore entered on with the view of ascer- 

 taining whether, with a small load on the end of the wire, the 

 temporary untwist produced by rise of temperature would be 

 changed to twist when the temperature exceeded a certain 

 limit. A few preliminary trials were made by merely heating 

 a portion of the permanently twisted wire with a burner ; and 

 it was found that when the wire reached a bright red heat a 

 most remarkable and sudden change occurred, the wire sharply 



* See above, the effect of increasing the load on the wire. 



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



