M. Gr. Wiedemann on Torsion. 99 



In the subsequent first-observed state of equilibrium the 

 agitation-effect may show itself in various ways. Sometimes 

 it consists merely of a rotation of the molecules about their 

 centre of gravity — as, for instance, on the diminution of the 

 permanent and the increase of the temporary magnetism by 

 the first agitations, heatings, &c. 



Further, the agitations may produce a turning of the mole- 

 cules about their centre of gravity without any directly per- 

 ceptible gliding of them over one another, which may only 

 afterwards have for its consequence an alteration of their dis- 

 placements on one another — as, for example, at the first alte- 

 rations (increase or decrease) of the load of a wire fixed in 

 an invariable position of temporary torsion (§10), by which, 

 after de torsi on, the permanent torsion of the wire is in- 

 creased in precisely the same manner as if the wire had been 

 frequently turned to the extent of its position of temporary 

 torsion. 



Finally, agitation may produce at the same time a rotation 

 of the molecules and their displacement on one another. This 

 appears, e. g., when a permanently twisted wire is shaken or 

 loaded, heated or magnetized, on which its permanent torsion 

 first diminishes (conf. my observations of 1858, and § 9 of this 

 paper). Herein is integrally included the result found by Braun 

 in 1876*, that permanent alterations in the shape of a body 

 in a determined direction are lessened by alterations in a di- 

 rection substantially different from and independent of the 

 former. 



The corresponding effect also results when a temporarily 

 twisted wire, which can freely yield to the pull of the torsion- 

 weights, undergoes changes of load, and thereby has both its 

 temporary and afterwards its permanent torsion increased. 



17. The effects of agitation (or accommodation actions) 

 might be conceived as similar to the diminution of the friction 

 of rough surfaces by rubbing them together. When deforma- 

 tion takes place in any wire, the groups of molecules present 

 are displaced in relation to one another, and their cohesion is 

 more or less impaired, so that they become movable and fol- 

 low further the forces acting from without than before. In 

 the " cracking " of tin when bent in one and afterwards in 

 another direction, the commotion of the entire mass corre- 

 sponding to these purely mechanical shiftings of the groups 



resistance to distortions, within the limits of their elasticity (?), become 

 less the oftener such distortions take place (Pogg. Ann. cliii. p. 406 ; 

 Wien. Ber. lxix. Marz 1874, p. 38 of separate impression). 

 * Pogg. Ann. clix. p. 337. 



H2 



