Tinfoil Grating Detector for Electric Waves. 445 



remained then only the supposition that the inner glass wall of 

 the bulb had become covered with a layer, by contact with 

 the alkali-metal, from which negative electricity escaped when 

 the light fell upon it. In order to remove this source of error 

 also the whole wall of the cell must be maintained at the 

 same potential as the anode of alkali-metal, so that there could 

 be no fall of potential from it to the wall. We attained this 

 result by covering the outside of the bulb with silver by pre- 

 cipitation; with the exception of a small space where the 

 kathode-wire was melted into the bulb and a " window " for 

 the entrance of the light. 



If now the alkali-metal surface and, with it, the glass wall 

 of the bulb was charged with positive electricity, and the 

 kathode-wire was connected to earth, then immediately after 

 ignition of the wire no loss of electricity occurred in light, 

 not even when a beam of sunlight entered through the window 

 in the silver coating. Eot until after some time, when the 

 wire on cooling had again covered itself with a coating of 

 alkali-metal, could the photoelectric discharge be again ob- 

 served with increasing distinctness. 



Thus the experiments with ordinary light on surfaces of 

 alkali-metal in a vacuum lead to the same result as those with 

 ultra-violet light, namely, that the photoelectric action is 

 limited to the kathode. 



We have pleasure in gratefully acknowledging the assistance 

 we have received in this work from the Elizabeth Thompson 

 Science Fund in Boston. 



XLVII. The Tinfoil Grating Detector for Electric Waves. By 

 T. Mizuno, Rigakushi, Professor of Physics, First Higher 

 Schools, Tokio*. 



§ 1. TNa paper f, which not long since I communicated to 

 JL this Journal, I suggested that the change of the 

 resistance of the grating might be due to a mechanical effect 

 exerted upon it by impinging trains of electric waves. In 

 other words, electric waves might give impulses to some of 

 the strips of the grating in such a way as to let leaflets on 

 their margins come in contact with one another, thereby 

 causing a diminution of resistance. In order to confirm this 

 view, further inquiries were carried out soon after the com- 

 munication of the above-mentioned paper. 



* From a separate impression from the Journal of the College of 

 Science, Imperial University, Tokio, Japan, vol. ix. part 2. Communicated 

 by the Author. 



t "Note on Tinfoil Grating as a Detector for Electric Waves," 

 Phil. Mag. vol. xl. p. 497 (1895). 



