488 Dr. R. Bernstein on the Influence of Light 



no doubt that this always took place in the interval between 

 any two consecutive inductive impulses ; for the duration of 

 these currents was indefinitely small as compared with the 

 intervals of time which elapsed between them. During the 

 whole time of the experiments the temperature of the room 

 increased from 13°*7 to 14°*3 C, and therefore could not have 

 been the cause of this observed increase in the resistance. 

 Since the same phenomenon was confirmed by a number of 

 further observations on other days, it appears conclusively 

 proved that 



The mere passage of electrical currents increases the resist- 

 ance of the thin layer of gold by more than one per cent., the 

 effect remaining for the space of about one day. 



Experiments by the Damping Method. 



In seeking for a further method which would enable the 

 sensitiveness to light of metallic plates, which were being 

 traversed by an electric current, to be observed in a manner 

 free from any disturbing secondary actions, the object to be 

 aimed at was to employ a current of minimum intensity, 

 without, however, diminishing the accuracy of the measure- 

 ments. It seemed as if this would be satisfactorily effected 

 by employing the "damping" method due to W. Weber*, 

 which consists in joining up the conductor, whose resistance 

 is required, with a galvanometer, and observing the oscil- 

 lations of the galvanometer-needle. In this way the metallic 

 plate under examination was only traversed by the feeble 

 currents induced in the coils of the galvanometer by the 

 swinging magnetic needle ; and, except in the first few ex- 

 periments, the metallic plate itself was included in the circuit 

 only at the moment when the deflections of the needle were 

 being read. The disturbing influence of the current was thus 

 reduced to a minimum: of course it was impossible to get 

 rid of it entirely ; and, moreover, this is not required for 

 qualitative experiments, since, fortunately, it operates in the 

 same way as heating would do, and thus can never be mis- 

 taken for the direct luminous effect. 



In the majority of the experiments carried out by this 

 method the source of light consisted of the flame of a Bunsen 

 burner coloured with salt, the rays being sent as before 

 through the slit, prism, and lens, onto the metallic plate ; on 

 a few subsequent occasions sunlight was employed. 



The experiments were made with gold, platinum, and silver. 

 Gold was employed as before, in the form of strips of gold 



* Weber, Elektrodynamische Maasbestimmunffen, Abh. der hgl. sacks. 

 Ges. d, W, Bd. I. S. 374. 1852. 



