498 



T. Mizuno on Tinfoil Grating as a 



waves, and an account of some experiments to determine the 

 nature of its action. 



2. I prepared my gratings by first coating a flat wooden 

 block with tinfoil and then cutting 



on it a number of fine parallel slits 

 with a sharp knife (see the annexed 

 figure) . 



A and B are binding screws 

 which are fixed in the block and 

 facilitate the connexion of the grat- 

 ing with a Wheatstone bridge. 



The particulars of the two grat- 

 ings chiefly used in my experiments 

 were as follows : — 



(1) Rectangular in form, 

 3*5 centim.by 5*1 centim., total 

 number of lines 97, and the re- 

 sistance nearly 130 ohms. 



(2) Also rectangular, 3'5 centim. by 4*4 centim., the 

 number of lines 118, and the resistance nearly 232 ohms. 



3. My primary vibrator was a brass cylinder 3 centim. in 

 diameter and 26 centim. in length, its surface interrupted 

 midway along its length by a spark-gap, and its ends fur- 

 nished with brass spheres 4 centim. in diameter forming the 

 poles. The wave-length of the electric waves produced was 

 ascertained to be about 60 centim. The vibrator was placed 

 in the focal line of a wooden parabolic cylinder coated inside 

 with tinfoil, whose height was 76 centim., depth 21 centim., 

 and focal length 12 centim. My resonator is very simple in 

 construction and has been found very convenient in my 

 other researches on electric waves. It is merely a rectangular 

 strip of tinfoil, 0*8 centim. in breadth and 60 (30 in some 

 cases) centim. in length, with a gap in the middle, which is 

 so fine that resonance-sparks can easily pass across. 



4. I will now describe some experiments (Exp. 1 . . . Exp. 6) 

 with the view of showing to what extent metallic gratings 

 can screen the action of electric waves. 



Experiment 1. 



A wooden board, on which were pasted two parallel tinfoil 

 strips, 33 centim. in length and at a distance of 9*7 centim. 

 from one another, was set up vertically in front of the para- 

 bolic cylinder at a distance of about 30 centim. from the 

 vibrator. The grating No. 1 was brought behind the board, 

 and after exposure for about half a minute to electric waves, 

 its resistance was examined by a Wheatstone bridge. The 

 results obtained were as follows : — 



