October 20th, 1896.] Proceedings. xi. 



" On a Mixture whose Electric Resistance depends 

 on the Magnetic Field in which it is placed." By 



Albert Griffiths, M.Sc. 



{Communicated by Professor Schuster, F.R.S.) 



The idea of examining this mixture originated in an 

 attempt to elucidate certain obscurities in the process of 

 electric conduction, such, for instance, as occur in the 

 case of bismuth, whose resistance increases in the magnetic 

 held. The mixture consists of a gelatine jelly containing 

 ferrous sulphate, iron filings, and powdered graphite ; the 

 object aimed at being the production of a conducting solid 

 with magnetic particles scattered throughout its mass. 



The jelly was allowed to set in a glass tube, copper 

 terminals being inserted before the solidification of the jelly. 

 The resistance so prepared was placed between the poles of 

 a large electro-magnet, whose field, with the current used, 

 was about 4,000 C.G.S. units. The tube w T as so arranged 

 that the electric current through it ran at right angles to 

 the lines of magnetic force. 



The experimental resistance was connected up with the 

 Wheatstone Bridge in the ordinary way, and measurements 

 were made both during the activity of the magnet and when 

 the magnet was unexcited. The results were fairly con- 

 cordant, and indicated a fall of the resistance in the magnetic 

 field of about 25 per cent. 



Mr. C. H. Lees and Mr. P. J. Hartog took part in the 

 discussion on the papers. 



