M. Gr. Wiedemann on Torsion. 9 



8. Influence of the Load. — I have already, in the year 1858*, 

 shown that, just as the breaking-off of a permanently twisted 

 iron wire by torsion through magnetizing is independent of 

 the weights with which the wire is loaded, so also, within 

 certain limits of loading (in oscillation-experiments), the 

 toughness of iron wires has the same independence of their 

 tension "f, and mentioned that this is not the case with silver 

 wires, especially at a higher temperature. A brief statement 

 of similar results respecting the increase of the toughness 

 with the load was published in 1865 by Sir W. Thomson f. 

 Braun also has recently § made experiments in the same di- 

 rection, concerning the action upon bodies of two deform- 

 ing forces in directions independent of one another ||. 



In connexion with those observations, to be communicated 

 later on, I first made some further experiments, on the static 

 conditions of wires which had been subjected to various forces 

 both of tension and torsion. For these experiments the 

 weighted iron rod suspended beneath the rod g of the torsion- 

 apparatus was replaced by a zinc beaker 21 centims. deep and 

 23 in diameter, hanging upon a horizontal bar. The beaker 

 was parted in the middle by a perforated zinc plate, in order 

 to avoid rotatory oscillations of the water with which it was 

 filled. Near its axis a glass tube of 5 millims. diameter, 

 nowhere in contact with the beaker, descended into it to 

 about 2 centims. from the bottom ; the glass tube was con- 

 nected with a vessel full of water by a caoutchouc tube ; and 

 by raising and lowering this vessel the level of the water in the 

 beaker could be varied. To the bottom of the tube was 

 cemented a setting which supported, concentric with the end 

 of the tube, a hemisphere of sheet brass about 2 centims. in dia- 

 meter. This, as well as the lower part of the tube, was bound 

 round with thick flannel ; so that the water flowed through 

 the tube into the beaker with very little velocity, and the 

 weight acted upon the wire, as far as possible, without shock 

 — which in experiments of this kind must be particularly 

 attended to, and cannot be secured by screw arrangements, 

 appending the weights by hand, &c. The mirror attached to 

 the torsion-apparatus remained in fact perfectly stationary 

 while, the wire being not twisted and the point h hanging 

 freely, water was introduced through the tube into or let out 



* Pogg. Ann. ciii. p. 575 (1858). f Ibid, cliii. p. 391 (1874). 



% Phil. Mag. [4] xxx. p. 63 (1865). 



§ Pogg. Ann, clix. p. 337 (1878). 



|| Here "belong indirectly the observations upon the stronger deadening 

 of the vibrations of strings and rods with greater tension and height of 

 tone. Compare A. Helmholtz, Toywmpjindungen, p. 122 ; Warburg, 

 Pogg. Ann. cxxxix. p. 89 (1870) ; Braun, ibid, cxlvii. p. 64 (1872), " Dis- 

 sertation," and cli. p. 260 (1874), 



