212 Mr. J. Brown on the Theory of Voltaic Action. 



me that the rate of decrease is quite independent of the 

 intensity of the first illumination. 



Diagram showing the Bate of Decrease of the Light given of by 

 Phosphorescent Paint. 

 Light 100 



75 



50 



25 



10 





5 10 20 40 60 



o Observed illumination. 



— — Curve calculated from the equation #' 86 = 



Minutes after 

 first observation. 



26-1 



' x+ -498' 



XXVIII. Theory of Voltaic Action. 



To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 



IN stating * that the results obtained by me f are due to a 

 difference of potential between the metal and its oxide, 

 chloride, or sulphide, Professors Ayrton and Perry continue 

 to ignore the concluding phase of these experiments, though 

 I have brought it prominently forward in the ' Electrician ' 

 for December 4, from which they give a quotation. I refer 

 to the fact that in the copper-iron ring experiments, though 

 after admission of the hydrogen-sulphide gas the copper side 

 becomes strongly positive to the iron, very soon this difference 



* Phil. Mag. for Jan. 1881, p. 48. 



t Phil. Mag. for Aug. 1878, p. 142, and Feb. 1879, p. 109. 



