THE 



LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOUKNAL OF SCIENCE. 



SUPPLEMENT to VOL. III. FIFTH SERIES. 



LXY. The Influence of Light upon the Electrical Resistance 

 of Metals. By Dr. R. Bornsteust, Assistant in the Physical 

 Institute, Heidelberg University*, 



THE object of the experiments described in this paper is to 

 prove the more general occurrence of a class of phe- 

 nomena which had hitherto been noticed only within narrow 

 limits, but which, nevertheless, were of such a nature as to 

 excite considerable interest among physicists in general. The 

 experiments are connected with the fact, which has been 

 noticed within the last few years, that the electrical resistance 

 of the metalloids selenium and tellurium diminishes if either 

 of these bodies be exposed to the action of luminous rays ; and 

 they have shown that the same phenomenon occurs in the 

 case of metals — that is to say, in the case of platinum, gold, 

 and silver. No other substances have as yet been examined ; 

 but the similarity in the behaviour of these three metals 

 renders it extremely probable that sensitiveness to light is 

 not, as one was hitherto inclined to think, a property peculiar 

 to selenium and tellurium, but that we are here dealing with 

 a general property of all metals. 



Both these metalloids are ill adapted for proving the phe- 

 nomenon of sensitiveness to light, inasmuch as they occur in 

 different and partially crystalline modifications, which behave 

 differently as regards the passage of electricity, and can be 

 converted, by means of heat, from one modification into the 

 other. Consequently the effect which is ascribed to light 

 may also, in certain circumstances, be produced in selenium 

 and tellurium by the action of heat ; and it is only certain 

 definite modifications of these metalloids which show the 

 reverse behaviour. This, however, is absolutely necessary in 

 order to prove that the observed diminution of resistance is 



* Translated and condensed by E. E. Day, M.A., the Owen's College, 

 Manchester. 



Phil Mag. S. 5. No. 21. Suppl. Vol. 3. 21 



