NOTE ON TINFOIL GRATING AS A DETECTOR FOR ELECTRIC WAVES. 



23 



The signs in the last column indicate the direction of the tinfoil 

 strips of the gratings with respect to that of the primary oscillations. 

 Thus, the answer may he taken as positive. 



< 6 C.ffl,-"> 



Experiment 12. 



Lastly I performed some experiments to decide the question 

 whether the change of resistance under consideration is a molecular 

 change as in a. selenium cell or simply a mechanical one. For this 

 purpose I prepared very carefully another tinfoil grating with a much 

 wider space between the strips. It was rectangular, 7 cm. in length 

 and 6 cm. in breadth, the total number of fine strips being 51. (See 

 the figure). 



The resistance of the grating thus 

 prepared was 209 ohms. 



Now exposing this grating to the 

 action of electric waves, I did not find the 

 least sign of change in its resistance, 

 except a very small one due perhaps to the 

 heating effect. The experiment was of 

 course tried several times and also on 



different occasions, but never with positive result. Here I wish also 

 to notice that although I tried the experiment with fine German- 

 silver wire and also fine iron wire gratings, I could never find any 

 decided effect due to the action of electric waves on them. 



7 cm 



Conclusions. 



I. It is certain that the change of resistance of the tinfoil 

 rating is due to the action of electric waves. So far as the electric 



