"er many essays, during which a great number 0 
in the Invisible Prismatic Spectrum. 173 
In May, 1882, I had the good fortune to secure one of the 
very large concave gratings, then newly constructed by Pro- 
Ls 
ae ten i ! ke for 
e 0 and, and which he was kind enough to ma 
yee 4 very short focus, so as to give a specially ae 
