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T. Mizuno on the Tinfoil Grating 



§ 2. Having constructed about forty gratings and tested 

 their action, I found to my surprise that while some were 

 extremely sensitive, others were not, being even utterly 

 indifferent to the impulses of electric waves, although they 

 had all been prepared with the same care and apparently with 

 the same success. 



This led me to undertake a closer examination of such 

 gratings, which gave results that throw much light upon 

 their nature. But before these results can be stated, it is 

 necessary to describe in detail my way of preparing the 

 gratings, because upon that their sensibility wholly depends. 



§ 3. The face of a flat wooden block of convenient size, say 

 10 centim. on a side, was pasted over with very fine tinfoil, as 

 described in my former paper. 



Then came cutting lines into the tinfoil, to which particular 

 attention was given. Along the edge of a bamboo ruler a 

 sharp knife, held always inclined away from the ruler, was 

 drawn lightly across the surface of the tinfoil. In this way 

 many fine parallel slits were cut in the tinfoil, 

 so as to make one continuous, regular, zigzag 

 line, as shown in fig. 1. 



A few of the gratings, thus carefully pre- 

 pared, were found to be sensitive. But 

 experience has taught me that success in 

 preparing good detectors depends, to a large 

 extent, upon the nature of the wood block on 

 which the tinfoil is pasted in the first place, 

 and next upon the degree of adhesion of the 

 foil to the wood. A soft wood is preferable 

 to a hard one, and the paste used should not 

 be thick enough to make the foil adhere too firmly. 



§ 4. The majority of the slits of the sensitive gratings, when 

 examined under a microscope, presented such an appearance 

 as that shown in fig. 2. A B and C D represent 

 two strips of foil with the very narrow slit or gap 

 a b between them that has been formed by the 

 knife. The shaded portion indicates the slope of 

 the tinfoil found at one edge of each strip. 



For the sake of clearness, there is shown in 

 fig. 3 an end view, that is, a section of the two 

 strips perpendicular to their lengths. The shaded 

 portions indicate the tinfoil strips, A B and D in 

 fig. 2, of which the edge of one strip, C D, extends 

 some distrance into the gap, a b, and forms the 

 slope mentioned above. Along this slope the tin- 

 foil presents many folds or wrinkles, which seems 



Fig. 2. 

 -Ar-T 



