ELLIPTIC INTERFERENCE WITH REFLECTING 

 GRATING. 



By C. BARUS. 



(Read April 21, 1911.) 



I. First Method. — There are two or three typical cases in the 

 use of reflecting gratings for the production of interferences in the 

 spectrum, each of which shows pecuharly interesting features. The 

 first of these is given in Fig. i and corresponds closely to the method 

 described for transmission gratings in a preceding paper. If L is 

 the source of light and M a glass plate grating, it was shown that 



Fig. I. Diagram, showing positions of mirror, M, and grating, G. 



plane mirrors in the positions Ci and G,,, each reflecting a spectrum 

 from M^ produce elliptical interference whenever the rays returned 

 after passing -1/ by transmission and reflection, respectively, are made 

 to overlap in the spectrum, under suitable conditions. 



The present method is the converse of this, since the gratings 

 and the opaque mirrors change places. Parallel rays from L strike 

 the plate of glass M and the component rays reach identical reflecting 



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