Science |3ragre 



35. 



No. 30. August, 1896. Vol. V. 



LIGHT AND ELECTRIFICATION. 



11. 



Continued from vol. Hi., p. 1S5. 



WHEN we come to consider how to imagine the 

 mode by which light discharges an electrified 

 surface, one of the first hypotheses is that it may be by a 

 kind of proof-plane action, the illuminated surface being 

 disintegrated and its charged molecules evaporated away, 

 taking their charges with them. 



The first objection to such a hypothesis is that the dis- 

 integrating action of light ought to be otherwise perceptible 

 either to microscopic inspection or to a delicate balance 

 which should determine the loss of material. 



It has, however, often been suspected that metals may 

 evaporate more or less, and the fact of their smell seems to 

 establish the fact, so it may be well to consider how small 

 a loss of material will serve to explain the observed loss of 

 electrification. 



If we assume that each molecule so evaporated has the 

 ionic charge on one of its atoms reversed, or, more simply, 

 if we assume that each atom carries off a quantity of 

 electricity of the order io -11 electrostatic unit, its maximum 

 possible and customary value, then the amount of electricity 

 associated with the one gramme of evaporated silver is 

 900 contants or 3 x io 12 electrodal units. 



30 



