

Detector for Electric Waves. 501 



large amount of change in resistance the latter gave no per- 

 ceptible resonance-spark. 



Experiment 6. 

 I have now placed my tinfoil grating within a glass bell- 

 jar which was covered with tinfoil strips. I found that even 

 in this case the change of resistance was distinctly perceptible. 

 Thus :— 



Experiment. 



Initial 

 Resistance. 



Final 

 Resistance. 



Decrease 

 of Resistance. 



1. 



2. 

 3. 



129-7 

 129-9 

 1299 



1250 

 125-7 

 125-6 



4-7 

 4-2 

 4-3 



This result may be taken to indicate how imperfect would 

 be the protection of an ordinary metallic gauze against 

 powerful electric oscillations. 



Experiment 7. 

 A circular copper plate 30 centim. in diameter was verti- 

 cally suspended in front of the vibrator. My tinfoil grating 

 placed behind the plate at a distance of about 12 centim. from 

 it showed the following changes in resistance : — 



Experiment. 



Initial 

 Resistance. 



Final 

 Resistance. 



Decrease 

 of Resistance. 



1. 

 2. 

 3. 



129-1 

 129-3 

 129 4 



1210 

 122-3 

 122-0 



8-1 

 70 

 7-4 



Next, the distance between the plate and the grating was 



diminished to 2*5 centim. 



The changes were as follows : — 



Experiment. 



Initial 

 Resistance. 



Final 

 Resistance. 



Decrease 

 of Resistance. 



1. 

 2. 

 3. 



1293 

 1290 

 1295 



1230 

 123-2 

 123-0 



6-3 



5-8 

 6-5 



