MAGNETISM AND TWIST IN IRON AND NICKEL. 



385 



Table III. 



Iron. 



Nickel. 



r = "0415 cm. 

 C — 16 amperes. 

 H=10'5. 

 H' = 77. 



r = "05 cm. 



C = 152 amperes. 



H=285. 



H'= 61. 



T 



10^6 



T 



io*-0 



11° 



100° 



11° 



100° 



48 



243 



439 



634 



828 



1030 



1260 



1450 



304 

 2-65 

 236 

 207 

 1-83 

 1-76 

 1-45 

 106 



2-89 

 2-60 

 217 

 1-93 

 1-83 

 1-64 

 1-52 

 1-33 



41 

 168 

 296 

 423 

 550 

 736 



2-90 

 294 



2-84 

 2-80 

 2-63 

 268 



218 

 239 

 2-42 

 250 

 2-65 

 255 



however, does not admit the sufficiency of this explanation. He entrenches himself 

 behind the argument, that however neatly Maxwell's explanation may seem to explain 

 the twist due to superposed magnetisms, it takes no cognizance of the reciprocal 

 phenomena (see Beiblatter, 1886, vol. x. p. 728). Professor J. J. Thomson has shown 

 (see his book Applications of Dynamics to Physics and Chemistry) that the existence 

 of the twist produced by passing a current along a magnetised wire requires that when a 

 current is passed along a twisted wire, or when a wire conveying a current is twisted, the 

 wire becomes magnetised. This result is deduced simply from the application of 

 recognised dynamical principles, and in no way takes account of any possible explanation 

 of either phenomenon in terms of simpler ones. There is, so to speak, no stepping behind 

 the scenes. It may well be doubted, however, if, after all, the experiments in which a 

 twisted wire conveying a current is found to become magnetised, can be regarded as 

 showing phenomena reciprocal to those in the experiments on the twisting of a magnetised 

 wire under the influence of a current passing along it. For in the latter the twist pro- 

 duced in the wire by the superposed magnetisms is always very small, far within the 

 limits of torsional elasticity; whereas in the former it is necessary to apply comparatively 

 large twists before any pronounced magnetic effect is obtained. In Professor Wiede- 

 mann's own experiments the twists applied are very large indeed for the length of wire 

 used, amounting to 7° per centimetre — that is, more than 200 times any of the twists 

 obtained in the experiments just discussed, and 40 times the largest twist which I have 

 ever obtained in like experiments. I have further found, by direct experiment, that it 

 requires an applied twist of 1° per centimetre to produce any pronounced magnetic 

 polarity in a wire conveying a current of half an ampere ; so that it seems to be quite 



VOL. XXXV. PART 9. 3 S 



