﻿[ 36 ] 



III. On Torsional Oscillations of Wires, By Dr. W. Peddie, 

 Physical Laboratory, Edinburgh University* . 



Sketch of Previous Work f. 



HPHE present subject is part of the more general one — the 

 JL deformations of a non-rigid solid. That strain, or part 

 of a strain, which disappears wholly on the removal of the 

 distorting stress, is called temporary strain : that which is 

 observed after the complete removal of the distorting stress, 

 is called permanent strain or set, though it may, and usually 

 does, diminish as the time which has elapsed since the com- 

 plete removal of distorting stress increases. The latter effect, 

 together with the converse effect of the gradual increase oi 

 set under continued constant stress, is called after-action by 

 the Germans. 



In 1835 (Pogg. Ann.) Weber investigated the laws of 

 permanent set of a stretched fibre. In 1837 (B. A. Report ; 

 see also B. A. Reports, 1843, 1844) Hodgkinson, as the result 

 of experiments on cast iron, came to the conclusion that " the 

 maxim of loading bodies within the elastic limit has no foun- 

 dation in nature " ; that is, permanent set is produced by any 

 stress however small. In 1842 {Ann. de Chim. et Phys.) and 

 1848 (Pogg. Ann. Ergbd. ii.) Wertheim observed that per- 

 manent set occurred in a previously undistorted body as the 

 result of any stress however small ; and in 1848 (Camb. & 

 Dubl. Math. Journ.) this limitation to Hodgkinson's statement 

 was independently pointed out, as a deduction from theory, 

 by Prof. James Thomson. On the other hand, a body pre- 

 viously distorted in a given sense may be again distorted to 

 a smaller, or the same, extent in the same sense without the 

 production of new permanent set. 



Between 1858 and 1862 G. Wiedemann made statical 

 experiments on the torsion of rods, in the course of which 

 he verified Wertheim's observation ; and in 1880 (Phil. Mag. 

 vol. ix.) he published the results of more extended experiments 

 of the same kind. One of these results is that, after repeated 

 twistings, alternately in opposite directions, by a given 

 couple, the set of a rod becomes constant ; and, if the rod be 

 again twisted, by increasing couples, in the direction of the 

 last twist, the strain (measured from the position of set) is 



* Communicated by the Author, having been read before the Royal 

 Society of Edinburgh, December 18, 1893. 



t This sketch is a mere outline. Fuller references will be found in 

 the papers quoted. 



