THE GRID STRUCTURE IN ECHELON SPECTRUM LINES. 

 Norton A. Kent and Lucien B. Taylor. 



Received July 7, 1921. Presented October 19, 1921. 



Some years ago Nutting ^ noted a peculiar, complex structure, 

 termed by him the "fluting" or "grid," which appeared in many 

 echelon spectrum lines, and consisted of several fine components of 

 different and often changing intensity. Later one of us ^ independ- 

 ently noted this structure. Nutting crossed the 12" Lummer plate 

 of the Bureau of Standards with his echelon and was apparently 

 forced to the conclusion that the structure was real — that is, that it 

 indicated an actual discontinuity of emission in the source. 



Proceeding on the assumption of reality, the writers attempted a 

 solution of the problem using LiX 6104 which, although known to be a 

 spectroscopic doublet, offered peculiar advantages in that the grid 

 was extremely brilliant, well-marked and persistent. 



Apparatus. 



The apparatus used consisted of: — 



Two echelons: No. 1, made by Porter, 30 plates, each 14.76 mm. 

 thick, step 1 mm., aperture 31.0 by 33.0 mm.; No. 2, made by Petit- 

 didier, 30 plates, each 23.29 mm. thick, step 1 mm., aperture 31.0 by 

 35.5 mm. 



The Bureau of Standards 12" Lummer plate kindly loaned by Dr. 

 Stratton. 



A Hilger Lummer plate — length 131 mm., width 14.5 mm., depth 

 4.827 mm. 



A Hilger constant deviation prism spectroscope combined with an 

 echelon as in Figure la; also a separate Hilger spectroscope with 

 another echelon spectroscope as in Figure lb. The achromatic lenses 

 of both echelon spectroscopes are of about 50 cm. focal length and 5 cm. 



1 Astrophys. Jour. 23, pp. 64 and 220. 1906. 



2 Kent, Proc. Am. Acad. XLVIII, No. 5. Aug. 1912. 



