Detector for Electric Waves. 



505 



7 cm 



t 



Now exposing this grating to the action of electric waves, 

 I did not find the least sign of 



change in its resistance except •< 6 em. ■>■ 



a very small one due perhaps 

 to the heating effect. The 

 experiment was of course tried 

 several times and also on dif- 

 ferent occasions, but never 

 with positive result. Here I 

 wish also to notice that al- 

 though I tried the experiment 

 with fine german-silver wire 

 and also fine iron wire grat- 



ings, I could never find any decided effect due to the action 

 of electric waves on them. 



■ Conclusions. 



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

 grating | s due to the action of electric waves. So far as the 

 electric discharges in the primary spark-gap are oscillatory, 

 they have an effect on the grating, but if not oscillatory, 

 none. 



II. Inasmuch as where my rectilinear tinfoil resonator fails 

 the tinfoil grating shows the presence of electric waves, the 

 latter must be regarded as far more efficient than the former 

 as a detector of electric waves. Even a single spark, if 

 oscillatory, is sufficient to produce a large effect on the grating. 

 I would here call attention to the fact that the change in 

 resistance of one and the same grating observed on different 

 days during the course of my research differed in amount. 

 This is certainly due to the conditions of the spark-gap, and 

 consequently the intensity of the primary oscillations, and 

 also somewhat to the time of exposure. 



III. The sensibility of gratings may, up to certain limits, 

 be increased by increasing the fineness and closeness of the 

 strips. For, of my two gratings which are nearly equal in 

 their dimensions but greatly different in the number of strips, 

 the first gave the maximum change of about 6 per cent., 

 while the second gave about 19 per cent. 



IV. The phenomenon under consideration may not be 

 molecular, and so far as my experiments go, seems to be 

 purely mechanical. Slits cut in tinfoil with a knife, however 

 sharp they may be, surely have margins which are zigzag. I 

 imagine that the action of electric waves may consist in giving 

 impulses to several strips of tinfoil so as to let the Leaflets on 



