18 KENT AND TAYLOR. 



Conclusion. 



Summarizing the above results, we may state that the evidence is 

 entirely against the existence of a discontinuity of emission in the 

 source. The grid is due to a secondary action of the echelon which 

 enters when the line under investigation is not sufficiently monochro- 

 matic. This means that the previous work of one of us ^ must be 

 considered as of small value and also that ^n explanation of the 

 apparent complexity of structure obtained by Nutting ^ can be 

 found in secondar}^ action. 



The results obtained emphasize the fact that when an echelon is 

 used to measure small wavelength differences, great care must be taken 

 to obtain the lines so narrow that their width is less than i Ao, else 

 secondary action may enter to cut off an edge of a line and thus give 

 a false intensity-maximum position. 



We must record our appreciation of the help rendered by various 

 student assistants, especially Alessrs. Greenleaf and Risga. We are 

 also indebted to Dr. Lucy Wilson for her skilful aid during part of this 

 research and to our assistants. Miss Pearson for mathematical work 

 in connection with the calculation of the constants of the echelons, 

 and Mr. Gilman for making the sketches accompanying this article. 



We wish also to thank sincerely the Rumford Committee of the 

 American Academy for numerous grants which made possible the 

 purchase of the main pieces of apparatus used in this investigation. 



6 Proc. Am. Acad., Vol. XLVIII, No. 5. Aug. 1912. 



7 Astrophys. Jour., XXIII, pp. 64 and 220. 1906. 



Physical Laboratory, Boston University, 

 May, 1921. 



