THE TINFOIL GRATING DETECTOR FOR ELECTRIC WAVES. 115 



fact that we can annul the change of resistance by completely 

 closing the top of the box with a metallic plate seems especially to 

 favour the above explanation. 



Experiment 3 : The grating was connected with the Wheat- 

 stone's bridge by means of two leading wires, and at the same time 

 placed inside the zinc box, just as in Exp. 2. After balance had 

 been well established and the top of the box closed, the primary 

 oscillations were excited. This time, the balance was at once des- 

 troyed and the resistance of the grating showed an appreciable 

 diminution, in spite of the fact of the grating being wholly enclosed 

 in a metallic box. Taking away one of the leading wires the 

 phenomenon yet remained the same, though the change of resistance 

 seemed somewhat smaller than in the former case. The leading 

 wires thus appeared to catch up electric oscillations and guide them 

 to the grating. Hence in experiments with electric waves it is 

 necessary to keep the grating free from any exposed wires, which 

 might easily take up electric disturbances. Such effects due to 

 leading wires were observed also by Herr Aschkinass during his 

 researches with these gratings. 



§ 7. To what extent the sensibility of the grating reaches will 

 now be quite clear from the results of the above experiments. It is 

 next of great importance to describe some experiments as to the 

 variation of the sensibility. In its primitive state, the grating 

 properly constructed is so sensitive that it can detect even the smallest 

 electric oscillations. But after having been used a few times, its 

 sensibility undergoes a sudden and decided diminution, and then 

 remains nearly constant. At first, when the grating is exposed to 

 electric waves and its resistance consequently diminished, a single 

 tap given to it is almost enough to restore the resistance to its initial 

 or primitive value. But when we have used the grating repeatedly, 



