404 



PROCEEDINGS OF THE AMERICAN ACADEMY 



TABLE OF WAVE-LENGTHS AND INTENSITIES : — Gro0p "6.' 



Plate I. At the head aiipears Angstrom's chart of the group, 

 enhirged four times. A map quite similar to this plate was pre- 

 pared and upon it was sketched, each day, the appearance of the 

 group as seen with the particular grating employed. The position of 

 any new line was estimated from its relation to those adjoining, and 

 the eyepiece scale was not used. The date, grating, power of eye- 

 piece, number of lines seen, and order of spectrum, whenever noted, 

 are given in the margin. The two sketches given on Dec. 17, 1879, 

 wei-e made with the help of a large collimating telescope of 6.7 centim. 

 aperture, and 1.62 centim. focal length, but it appeared to possess 

 little, if any, advantage over the shorter collimator. On Jan. 2, 1880, 

 the chart was made from one flint glass and one bisulphide of carbon 

 prism, each prism having a refracting angle of 60°. AVhere two lines 

 were not separated by the 2540 gratings, I have indicated the fact 

 by blending them upon tlie chart ; and where there was any question 

 as to the visibility of a line, an interrogation mark has been placed 

 opposite. 



Plate II. gives the final determination of the '*i" Group upon :i 

 scale four times that of Angstrom, and also .«hows the group as given 

 in the charts of Kirchhoff and Anfrstrom, the scale beincj unaltered 

 in either case. Angstrom gives 20, Kirchhoff 17 lines. The chart con- 



o 



tains all the lines given by Angstrom, together with such additional 



