404 



Prof. Henry A. Rowland on C 



rratings 







Minima where Intensity is 0. 

 Wave-lengths. 



Maxima where Intensity is 1. 

 Wave-lengths. 



1st spec... 

 2nd „ ... 

 3rd „ ... 

 4th „ ... 



5th „ ... 



•0000526 

 •0000500 

 •0000462 

 •0000416 



&c. 



•0000268 

 •0000266 

 •0000263 

 •0000259 



&c. 



•0001000 

 •0000833 

 •0000651 

 •0000499 



1 &c. 



1 



•00003544 

 •00003463 

 •00003333 

 •00003169 

 &c. 



•00002137 

 •00002119 

 •00002089 

 •00002050 

 &c. 



The central light will contain the following wave-lengths as 

 a maximum : — 



•0001072, -00003575, -0000214, &c. 



Of course it would be impossible to find a diamond to rule 

 a rectangular groove as above, and the calculations can only 

 be looked upon as a specimen of innumerable light distribu- 

 tions according to the shape of groove. 



Every change in position of the diamond gives a different 

 light distribution, and hundreds of changes may be made 

 every day and yet the same distribution will never return, 

 although one may try for years. 



Example 2. — Triangular Groove. 



Let the space a be cut into a triangular groove, the 

 equations of the sides being x=—cy and x=c'(y — a), the 

 two cuttings coming together at the point y = u. Hence we 

 have — cu = c ( (u — a), and ds = d?/~\/l + c 2 , or dy*/l+< 

 Hence the intensity is proportional to 



70 f 1 + c 2 . 9 iru(u, — c\) . 1 + c' 2 



/2 



(/JL — C\) 



2Sm I ~ + (fl+c'\y 



sin 



7r(a— u)(/jl + (/\) 

 I 



V(l4-o 2 )(l+o /2 ) dn 7r^ / ,-cXJ c . n 7r(a-^)( / , + ^ ) 

 (fi— cy)(fju-\-c'\) I I 



cosjlip + c'\)(a— w)— n(fi— ck)] I 



This expression is not symmetrical with respect to the normal 

 to the grating, unless the groove is symmetrical, in which case 



c — d and u= K . 



