486 Dr. R. Bornstein on the Influence of Light 



then cemented side by side in an upright position on to a 

 larger glass plate, so that the gold leaves were parallel and 

 vertical ; and then the arrangement was placed in the position 

 previously occupied by the observing-telescope in the appa- 

 ratus already employed ; and the gold leaves were included in 

 the circuit by means of their connecting wires, just in the 

 same way as the platinum wires had been. A simple slot in 

 the table which carried the whole of the apparatus allowed 

 the glass plate, carrying the gold leaves, to be rapidly slid 

 along, so that one and then the other was alternately within 

 reach of the rays coining from the prism. All the other 

 arrangements remained exactly as before. The length of 

 each of the gold leaves, between the tinfoil coatings, was 

 24 millims., and its width 9 millims., while its resistance was 

 about 3 mercurial units. 



The results obtained in these experiments corresponded 

 exactly with those previously arrived at with the platinum 

 wires; and we may therefore combine them briefly as fol- 

 lows : — 



Platinum and gold exhibit a diminution of resistance in con- 

 sequence of illumination — the diminution, it is true, being quan- 

 titatively of small amount, but qualitatively quite sufficient clearly 

 to establish the reality of the fact. 



Experiments with Weber s Magneto-Inductor. 



In all the experiments in which the Wheatstone-bridge 

 arrangement was employed the changes of conductivity, due 

 to exposure to light, which could be detected in platinum and 

 gold, were very small, hardly amounting to more than 0*01 

 per cent. It was impossible to tell from these experiments 

 whether there was any secondary action, connected with the 

 method of observation, which interfered with the luminous 

 effect ; for both the metallic bodies which were examined on 

 each occasion were, throughout the experiment, in exactly 

 the same circumstances, the only difference consisting in their 

 illumination. If any unfavourable influence was present, it 

 would be present invariably, and therefore could not be de- 

 tected by any comparative experiments. But, as soon as the 

 earlier experiments had shown that there was in all proba- 

 bility a real diminution of resistance in consequence of illu- 

 mination, it appeared desirable to discover a second method, 

 which would establish the same fact in another way. The 

 first point consisted in separating the metallic bodies under 

 examination ; and henceforward each of them was always ex- 

 perimented upon by itself. One of the gold leaves, already 

 referred to, was first examined, the method of illumination 



