448 



T. Mizuno on the Tinfoil Grating 



R* 5. 



the resistance of the grating was diminished by from 1 to 

 nearly 2 ohms. 



The experiment was repeated after raising the plate, ADC, 

 parallel to itself and keeping it at some height from the 

 aperture, AC. Similar changes of resistance were also ob- 

 served in this case. This phenomenon may of course be 

 understood by considering the fact that some electric waves, 

 which pass out of the uncovered portions of the parabolic 

 vibrator, will, after going through the room and being reflected 

 from the surrounding walls, ceilings, &c, come back ultimately 

 to the grating in a much enfeebled state. 



Experiment 2. The above experiment was modified by 

 placing on the plate, A D C, a 

 zinc box, abed, 17 centim. by 

 27 centim., without top or bottom 

 and putting the grating inside it. 

 In this case also, a change of 

 resistance was observed, though 

 smaller. It is then certain that 

 although the side effects were 

 got rid of, the top effect still 

 remained, through which traces 

 of waves might affect the re- 

 sistance of the grating. The 



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 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 destroyed 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 



