532 Royal Society: — Mr. H. Tomlinson on the Increase 



polarized ray, as T had anticipated. When the light was reflected 

 from a south pole the plane of polarization was rotated to the 

 right of the observer, which is the direction of rotation assumed 

 in my explanation. 



I next covered a portion of the polished face with gold leaf, as 

 Professor Barrett had suggested ; and now the light reflected from 

 this diamagnetic substance was unaffected by the magnetism, as 

 I had also anticipated. I exhibited all these effects to Mr. Stoney, 

 who entirely confirmed my observations. 



The angle of incidence in the experiments described above was 

 about 60°. If the incidence were either perpendicular or grazing, 

 the theory which I have proposed would lead to the conclusion 

 that the angle between the major axis of elliptic polarization and 

 the original plane of polarization would vanish. If, accordingly, 

 the observation can be made at a perpendicular incidence, and if 

 the Nicol's prisms be so placed as to extinguish the light before 

 magnetizing the iron, then on exciting it light ought to reappear, 

 as it does at oblique incidences ; but the field should not become 

 darker on moving the analyzer. 



I attribute great weight to the verification of my theory arising 

 from the fact that the polarization of the reflected ray is found by 

 experiment to be in general elliptic, and also from the fact that there 

 is no appreciable effect when gold, a diamagnetic substance and 

 therefore feeble, is substituted for iron. 



Since communicating my paper, I learn, through Professor Stokes, 

 that when Mr. Kerr's paper was read before Section A of the 

 British Association, both he and Sir W. Thomson spoke of the 

 possibility of connecting Mr. Kerr's result with a powerful double 

 refraction of the same kind as the feeble double refraction shown 

 by transparent substances under the influence of magnetism. It 

 is a connexion of this kind which I have endeavoured to de- 

 monstrate. 



" On the Increase in Kesistance to the Passage of an Electric 

 Current produced on Wires by Stretching." By Herbert Tomlinson, 

 B. A., Demonstrator of Natural Philosophy, King's College, London. 



The object of this inquiry was 



(1) To determine the relation between increased resistance 

 to the passage of an electric current and stretching force. 



(2) To ascertain how much of the increased resistance in each 

 case is produced by mere increase of length and diminution of 

 section of the stretched wire. 



In order to determine the increase of resistance from stretching, 

 the wires were each divided into two parts, about 14 ft. in length ; 

 one end of each part was fastened to a stout hook firmly fixed 

 into a block of wood. These two hooks were about 8 inches 

 apart, and the block of wood in which they were fixed was securely 

 fastened across two uprights placed resting against a w T all of the 

 room, so that the weights, which were attached to the other ends 



