THE 



AMERICAN JOURNAL OF SCIENCE 



[THIRD SERIES.] 



Art. XXX. — The Absolute Wave-length of Light ; by Lotus 

 Bell. Part II. 



[Continued from page 282.] 



This continuation of my previous paper contains the angular 

 measurements and the details of the measurement and calibration 

 of the gratings, together with the final results. In addition I 

 have endeavored to point out the probable sources of error in 

 some recent determinations of absolute wave-length. 



Angular Measurements. 



In my former paper (this Journal, March, 1887) the work 

 with glass gratings was described in detail, so that it will only 

 be necessary to summarize it here. 



Grating I was used during October and November, 1886, and 

 forty- eight series of observations were obtained as follows, each 

 series consisting of three to seven observations. 



Date. 



Number of 



series. 





Angle. 



Oct. 19, 



1 







45° 1' 4V"-2 



20, 



1 







45 1 48 -4 



22, 



2 







45 1 48 -2 



23, 



1 







45 1 49 -8 



26, 



4 







45 1 49 -3 



27, 



3 







45 1 48 -2 



81, 



1 







45 1 50 -1 



Am. Jour. Sci.— 



-Third Series. — Vol. 



XXXV, 



No. 



209.— May, 1888 



21 











