332 Mr. S. Bidwell on the Generation of 



the immediate movement of the spot of light through 50 scale- 

 divisions indicated a diminution of the current. When the 

 magnesium was extinguished, the current at once increased 

 to its original strength. When a nearly red-hot brass rod 

 was held at a distance of 3 centims. from the silvered surface, 

 the current slowly increased in strength ; and when the hot 

 rod was removed, the current was again slowly diminished. 

 The effects both of light and of heat were verified by many 

 repetitions of the experiments. These results which, so far as 

 regards the effect of light, were unexpected, are of the same 

 character as those described in (1). I have elsewhere* given 

 strong reasons for believing that the combination of sulphur 

 with silver is assisted by the influence of light. If this is so, 

 it is certainly a remarkable fact that increased corrosion of the 

 silver electrode should be accompanied by diminution of the 

 current. 



Two days afterwards the silver-leaf had become much dis- 

 coloured, and was in some parts quite black. When con- 

 nected with the galvanometer the cell gave a current of nearly 

 the same strength as before; but now it was found to be 

 slightly increased by light as well as by heat ; and it is pro- 

 bable that the light as such exerted no influence whatever, 

 the observed effect being really due to the incidental rise of 

 temperature. 



(12) The silver-leaf was scraped off, and the surface of the 

 sulphur mixture having been cleaned from all visible traces 

 of free silver with fine emery-cloth, a piece of thin gold- 

 leaf was pressed upon it. It w r as found very difficult to make 

 it adhere satisfactorily. The cell, when connected with the 

 galvanometer, gave no indication whatever of a current. 

 When the cell described in (2) was also inserted in the circuit, 

 the spot of light was deflected, showing that the first cell was 

 quite able to conduct electricity, and that its failure to origi- 

 nate a current w r as not owing to bad contact between the gold- 

 leaf and the sulphur mixture. 



(13) A cell containing a mixture of sulphur and silver 

 sulphide between plates of silver and iron was found to have 

 an E.M.F. of '023 volt, or about one third of that of the silver- 

 copper cell described in (2). The direction of the current 

 was the same. 



(14) A cell was made by melting sublimed sulphur upon 

 a plate of copper and pressing a plate of iron upon the melted 

 sulphur. On connecting it (when cold) with the galvano- 

 meter, there was no indication of any current. Nevertheless 

 the cell was found to conduct electricity very well wdien a 



* Phil. Mag. August 1885. 



