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38 Proceedings of the American Philosophical Society. 
The object of Messrs. Smith and Mason was to furnish a minute de- 
scription of some of the principal nebule in the heavens, in order that 
future changes in their appearance, should any occur, may be detected. 
The process employed was—Ist. To prepare an accurate chart of all the 
stars in and about the nebula, capable of micrometrical measurement. 
Qdly. To fill in with the smaller stars down to the minimum visibile, by 
estimation. 3dly. To lay down the nebula on this chart with such care 
and precision, that the errors of its delineation may not far exceed those 
of original vision. The author, Mr. Mason, states at Jength the expedi- 
ents used to effect the latter purpose, viz. the drawing of lines of equal 
brightness, as a guide to the engraver ; the examination of each portion 
of the nebula by several persons ; and lastly, the repeated comparison of 
the drawings with the original on successive evenings, till no further im- 
provement seemed to be practicable. 
The telescope used by Messrs. Smith and Mason, was of their own 
construction. It was fourteen feet in length, and had twelve inches clear 
aperture, being a Herschelian, mounted somewhat rudely on the plan of 
Mr. Ramage. The difficulties experienced by Messrs. Smith and Mason, 
as amateur artists, in casting and polishing specula at New Haven, are 
stated in detail. The telescope was capable of separating ¢ Orionis, 
u? Bootis, 7 Virginis in 1838, 4 Ophiuchi, and others of a distance of 
less than 1”. For such purposes, however, the use of diaphragms was 
necessary, owing to an imperfection of the casting, and the full light of 
the telescope could not be employed. This circumstance directed their 
attention to the subject of this paper. 
A cursory examination of the principal nebule described, and, in some 
instances, figured by the Herschels, pointed out discrepancies between 
-their descriptions and present appearances, which must be attributed 
either to a change in the nebule themselves, or to the want of sufficient 
minuteness of examination on the part of the Herschels, whose object 
was rather the formation of a complete catalogue of the nebule in the 
heavens, than the fall and perfect description of any of the individuals. } | 
Thus, the paper contains a drawing of the “nebula trifida,” h. 1991: the 
triple star does not occupy the same position in the cleft as given in the 
figure in Sir J. F. W. Herschel’s. paper, Phil. Trans. 1833, but rather 
adheres to the left of the three divisions; and what is more remarkable, 
the small star about 30! north of this triple star was surrounded with 4 
nebula not much inferior in size and brilliancy to the “ nebula trifida.” 
A drawing is also furnished of the nebula, h. 2008, (the shape of which 
resembles the capital Greek ©,) with a critical examination of Herschel’ 
figure of the same. 
The most remarkable discovery of Messrs. Smith and Mason, was that 
of the junction of the two nebule, h. 2092 and 2093. These grett 
nebule, or “milky ways,” are described on several occasions by the elder 
