Spectre of the Stars and Planets. 423 
It is not worth while to describe the various forms of spec- 
troscope that have been employed in the last ten years, quartz, 
Iceland spar, hollow prisms and flint glass have been the 
materials, and they have been sometimes direct vision and 
sometimes on the usual angular plan. Gratings on glass and 
speculum metal given to me by Mr. Rutherfurd have been 
Which are devoid of yellow color; the an Saaee 0 
e plate in fron 
poses that a reflector which brings all the rays from the star, 
no matter what their refrangibility, to a focug in one plane, 
plane of the rays in the middle of the spectrum, and in observ- 
lens for the ultra violet rays. It is easy therefore with a 
refractor so to adjust the position of the slit that you may have 
4 Spectrum tolerably wide at F and G, and which gradually 
diminishes in width toward H, and finally becomes almost 
linear at M. Now as the effect of atmospheric absorption on 
