THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOUENAL OF SCIENCE. 



[FIFTH SERIES.] 



JANUARY 1880. 



I. On Torsion. By Gustav Wiedemann*. 



[Plate I.] 



1. O INCE M. Weber, in 1835, studied the laws of the tem- 

 ^ poral course of the permanent elongation remaining 

 after the cessation of a temporary stretching of a thread (the 

 elastic effect) f, and in 1841 advanced as the cause of the elon- 

 gation " the difference of the position of the axis of elasticity 

 of the smallest particles at any instant from that which corre- 

 sponds to, and is determined for each tension at, perfect equi- 

 librium," an opportune observation by R. Kohlrausch (in 

 1847)} has been followed by a more extensive series of inves- 

 tigations upon the relations of imperfect elasticity. These 

 have been carried out essentially in two different directions. 

 In the one set the temporary and the permanent alteration of 

 form are in part observed directly, as well as in their temporal 

 course ; in the other the diminution of the length of swing of 

 oscillating bodies. 



In the experiments of the latter sort (for example, on tor- 

 sional oscillations) the molecules are immediately transferred 

 from the positions assigned to them by the forces acting at 

 any instant to other positions, before the elastic afteraction has 

 ended ; and consequently the phenomena are highly compli- 

 cated. It therefore appeared to me advisable, before studying 



* Translated from Wiedemann's Annalen, 1879, No. 4, vol. vi. 

 pp. 485-520. 



t Pogg. Ann. xxxiv. p. 247 (1835), liv. p. 1 (1841). 

 \ Pogg. Ann. lxxii. p. 393 (1847). 



Phil. Mag. S. 5. Yol. 9. No. 53. Jan. 1880. B 



