[ 153 ] 



XX. Proceedings of Learned Societies. 



ROYAL SOCIETY. 



[Continued from p. 84.1 



June 17, 1875. — Joseph Dalton Hooker, C.B., President, in 

 the Chair. 

 r FHE following Papers were read: — 



" On the Change produced by Magnetization in the Electrical 

 Resistance of Iron and Steel. — Preliminary Notice." Communi- 

 cated by Professor W. G. Adams, E.B,.S. 



For some time past Mr. Herbert Tomlinson, Demonstrator in the 

 Physical Laboratory of King's College, has been engaged in 

 carrying out a series of experiments on this subject, and also on 

 the effect of change of tension on the electrical resistance of steel 

 and iron wires. 



In measuring the resistances of the short lengths of the wires 

 or rods which were employed, a unit was chosen which was a 

 small fraction of the British-Association unit. 



Experiments were made with rods of soft iron about one eighth 

 of an inch thick, with soft steel, and also with steel of different 

 degrees of hardness. 



With a rod oi: soft iron about 3 feet long there was an increase 

 of resistance of about 1 per cent, on magnetizing with two Grove's 

 cells. The whole resistance of this rod was 32 units. 



The experiments were repeated with the rod placed in ice and 

 also in water at the ordinary temperature (about 15° C), and with 

 nearly the same change in the resistance of the rod. The change 

 in the temperature of the water was found to be about 1° C. during 

 the experiment. 



Another rod of soft iron was employed whose resistance was 50 

 units. The magnetizing current was measured by means of a tan- 

 gent-galvanometer, and the resistance was measured by means of 

 Wheat stone's bridge. There was found to be an increase in the 

 resistance of the rod when it was converted into a magnet by 

 sending the magnetizing current through a wire which was coiled 

 round it in the form of a spiral. 



It was found that the electrical resistance was increased when 

 any addition was made to the strength of the magnetizing current. 

 When the increase in the electrical resistance was divided by the 

 square of the strength of the magnetizing current, a series of 

 numbers was obtained which did not differ much from one 

 another ; the values of these numbers mostly lie between 3 and 4. 



When the magnetizing current is considerably increased, the 

 ratio of the increase in the resistance to the square of the mag- 

 netizing current diminishes rather rapidly. 



A similar series of experiments was made with a thick knitting- 

 needle made of soft steel. The resistance of the needle was 29 

 units. In this case also the resistance was found to increase when 



Phil Mag. S. 5. Vol. 1. No. 2. Feb. 1876. M 



