NOTE ON TINFOIL GRATING AS A DETECTOR FOR ELECTRIC WAVES. 21 



their focal lines should be parallel. My tinfoil grating No. 2 was 

 held in the focal line of the second parabolic cylinder and tested ; 

 thus : — 



Taking away the cylinder, I found : 



Experiment 10. 



In this experiment, my tinfoil grating No. 2 was placed just in 

 front, of a metallic plate, that is to say, near the node of the stationary 

 electric waves produced by the plate, with the following results : — 



Taking away the plate, I found : — 



