C. Burns — Interference of Reversed Spectra. 423 



Rowland concave reflecting grating G' with the strong lens at 

 T, the grating receiving a beam of parallel rays of light for 

 each color from the collimator and first grating G. In this case, 

 with sufficiently high dispersion, a large strong field was 

 obtained, in which even the very fine lines of the solar spec- 

 trum were quite sharp. Rotating the grating G' around a 

 parallel horizontal axis, like AA, made little difference, rela- 

 tively speaking ; but rotation around the axis e normal to its 



Figs. 7, 8, 10, 11. 



4= 



e 



&q.7 



/■ — N, 



( $> ) 



V___^ 



f*) e 



cA 



zz 



plane, carried out by actuating a and o in opposite directions, 

 made fundamental differences in the appearance of the phe- 

 nomenon and eventually suggested a new interferometer for 

 homogeneous light. 



The adjustments are the same as in case of fig. 5 (G being 

 the transparent grating) except that G' is now a concave grat- 

 ing, and T a strong eyepiece. The distances G ' T and GT 

 were of the order of one and two meters. The first experiments 

 with the new and powerful apparatus (plane transparent grat- 

 ing G, grating space 351 xlO~ B cm., and the concave reflecting 

 grating G', grating space 173 XlO" 6 cm., fig. 8) were made 

 with the object of verifying, if possible, the reaction of parallel 

 ether wave trains on each other across a very narrow ether gap. 

 The sodium arc lamp was used as a source of light. The results 

 as a whole were negative, or at least conflicting. When the 



