No. 144.] 105 



New- York J March 8, 1855. 

 Mr. Henry Fitz : 



Dear Sir — In reply to your request for some information as to 

 the character and performance of your nine inch object glass, I 

 must premise by saying that I have had no weather since your 

 last work upon its surfaces, fine enough to do ample justice to a 

 telescope of its dimensions, and before your request I was rather 

 engaged in prosecuting my double star measurements than in 

 searching for such tests as would convey an idea of its powers. I 

 can, however, safely say, that considering its most unusual pro- 

 portions, nine inches aperture and nine feet focal length, its cor- 

 rections both for color and spherical abberration, are remarkably 

 perfect. In running the eye piece inside of the focal point, the 

 margin of the image of a white star is of a bluish claret; in 

 coming out, a rather decided green j and the color of the moon 

 and Saturn remain unchanged with high powers. The magnified 

 disks of stars inside and outside the focal points, are of almost 

 equal and uniform dilation, whilst the fucal point itself is one of 

 the extremest nicety, the slightest variation from which, in either 

 direction, is at once fatal to definition. I am sorry that I am not 

 able to refer you to any very good tests of its illuminating power. 

 The only ones which now occur to me are the following : I saw 

 the companion of Polaris a few days since, nine minutes after the 

 sun had ceased shining, and last night I distinctly perceived by 

 averted vision, the " star dust " composing the so called nebula 

 near the tip of the Bull's southern horn. On both these occa- 

 sions, the air, though clear, was extremely disturbed and unfa- 

 vorable. Saturn in a good atmosphere is shown clear and sharp, 

 without stray light or haze, on a black ground. On many occa- 

 sions I have seen the shaded line in the outer ring, which, with 

 smaller power, appears like a division, but which, I am satisfied, 

 is not at all analogous to the dark, well defined line which sepa- 

 rates the inner and outer ring. The new dark ring is also well 

 seen, having its margin nearest the planet sharply defined, and 

 its color though sombre indeed, well contrasted with the black 

 space adjoining. 



