■ 



Tinfoil Grating as a Detector for Electric Waves. 497 



one-quarter or three-eighths of an inch, and necessarily, there- 

 fore, of greater effective cross-section. 



It may also readily be seen by inspection that a needle of 

 finite length reduces the effectiveness of all the small-diameter 

 turns along the axis of the coils, thus showing that the waste 

 axial space in ordinary constructions is not of such serious 

 amount relatively, but on the other hand further supporting 

 the other arguments for the employment of a very short 

 needle. 



In the interest of uniformity of convention this opportunity 

 is taken to urge upon those who describe sensitive galvano- 

 meters, and especially instrument-makers in cataloguing, that 

 they invariably present the data : 



d = deflexion in mm. with scale at 1 metre from galvano- 

 meter. 

 c = current in amperes producing that deflexion. 

 g = the galvanometer resistance as connected up when 



d is observed. 

 t — the time of single swing of the needle when c is 

 measured. 

 These permit the computation of the several measures of 

 sensitiveness : 



d _d_ _d__ 10^ 



c c s/g c \/g t<2 



so useful in the comparison of instruments, and so essential 

 to an intelligent selection for specific purposes. 



Rogers Laboratory of Physics, 



Massachusetts Institute of Technology, 



Boston, September, 1895. 



XL VI. Note on Tinfoil Grating as a Detector for Electric 

 Waves. By T. Mizuno, Rigakushi, Professor of Physics, 

 Daiichi Koto Gakko * . 



1. ~]\/| UGH interested by Herr E. Aschkinass's experiments 

 -L-^J- described in his paper read before the Physical 

 Society of Berlin, I have been induced to repeat them. How 

 far my results confirm his and how far they differ from them 

 will be seen from this note, in which I also give a few tests 

 of the sensibility of tinfoil grating as a detector of electric 



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

 Science, Imperial University, Tokio, Japan, vol. ix. part 1. Communi- 

 cated by the Author. 



