■NOTE ON TINFOIL ORATING AS A DETECTOR FOR ELECTRIC WAVES. 25 



grating once diminished by an exposure to the action of electric 

 waves can be restored nearly to the original value by tapping the 

 grating. It may be pointed out that Prof. Minchin's experiment* on 

 the action of electromagnetic radiation on films containing metallic 

 powders may stand in close connection with the present subject. 



* Phil. Mag. p. 90. 1894. 



I 



