272 M. C Lea—Action of the less refrangible rays of Light 
apers were next blotted off in clean filtering paper 
(because if hung up to dry, the lower end becomes more richly 
running water and dried. In a few cases specially mentioned, 
the silver solution was allowed to dry on the paper for compar- 
ative experiment. 
Rep Rays. 
Examination of the Glass.—The ruby glass of commerce dif- 
fers very much in different specimens; some pieces, though 
appearing to the eye to be of a strong, pure red, nevertheless 
transmit a good deal of green light, and show in the spectro- 
tion spectrum traces of the more refrangible rays. The band 
which represents the proper color extends from very near the 
extreme red end to a point a little beyond the double sodium 
line D. 
? 
desire to make these investigations, as far as possible, absolutely 
i a 
these two was very striking. 
With tvo stronger red plates, having a limit of A600, and of 
course a diminished illumination, no trace of an image by devel- 
