322 Royal Society: — Prof. W. G. Adams on the 



lation (such as the doubts raised by the author as to the original 

 fluidity of the earth) speak for themselves ; and the reader may be 

 expected to take discussions of such questions for what they are 

 worth. 



XXXIX. Proceedings of Learned Societies. 



ROYAL SOCIETY. 



[Continued from p. 249.] 



January 6, 1876. — Joseph Dal ton Hooker, C.B., President, in 

 the Chair. 



'TUIE following papers were read : — 



11 On the Action of Light on Tellurium and Selenium." 

 By Prof. W. G. Adams, F.E.S. 



Two platinum wires were attached to the ends of a small 

 bar of tellurium, about 1 inch in length, by heating the wires to 

 a bright red heat and bringing them suddenly into contact, one with 

 each end of the bar. The platinum wires melted a small portion 

 of the tellurium, and became imbedded in it. The resistance of 

 the bar and wires was about half an ohm. The tellurium was 

 placed in a box, and its resistance balanced; then it was exposed 

 to the light of a paraffin-lamp, just as in the experiments with sele- 

 nium. At first the light seemed to have no effect ; but in con- 

 sequence of the heat from the lamp, the resistance of the tellurium 

 was increased. 



On placing a rectangular vessel of water between the lamp 

 and the tellurium and then exposing as before, there was no change 

 of resistance in the tellurium, showing that if there was any dimi- 

 nution in the resistance due to the action of light it was entirely 

 balanced by the increase in the resistance due to heating by the 

 current and by the residual portion of the radiant heat. 



On replacing the rectangular vessel of water by a beaker of 

 water, so as to focus the light of the lamp on the tellurium, there 

 was found on exposure to be a diminution in the resistance of the 

 tellurium, which gradually increased until the galvanometer-needle 

 was deflected through 30 divisions of the scale. The needle was 

 then brought back to zero by altering one of the slide-resistances 

 in the circuit. The agreement between the amounts of the change 

 of resistance in several successive experiments, with intervals be- 

 tween them, was very close. Thus, in three experiments on October 

 8th, 



The change in the first experiment was 124 millims. of wire, 



„ second „ „ 120 „ „ 



„ _ „ third „ „ 122 „_ „ 



showing a diminution in the resistance of the tellurium amounting 



to about one thousandth part of its whole resistance on exposure 



to the light of the paraffin-lamp. 



On repeating the experiments with the tellurium which had not 



