through a mist, and sometimes as nebulous specks, which might be, and not ! 

 unfrequently are, mistaken for comets. With ordinary telescopes these ob- 

 jects are visible in very considerable numbers, and were observed nearly a 

 century ago. In the Connaissance des Temps, for 1784, Messier, then so cele- 

 brated for his observations on comets, published a catalogue of 103 objects of 

 this class, of many of which he gave drawings, and with which all observers 

 who search for comets ought to be familiar to avoid being misled by their re- 

 semblance to them. The improved powers of the telescope speedily disclosed 

 to astronomers the nature of these objects, which, when examined by sufficient 

 magnifying powers, prove to be masses of stars clustered together in a manner 

 identical with that cluster in which our sun appears to be placed. They ap- 

 pear as they do, mere specks of whitish light, because of their enormous dis- 

 tance. Many of them are of a round figure, and convey the idea of a globular 

 space filled full of stars insulated in the heavens, and constituting in itself a 

 family or society apart from the rest, and subject only to its own internal laws. 

 The task were vain to attempt to count the stars in one of these globular clus- 

 ters. They are not to be reckoned by hundreds ; and on a rough calculation, 

 grounded on the apparent intervals between them at the borders (where they 

 are not seen projected on each other), and the angular diameter of the whole 

 group, it would appear that many clusters of this description must contain at 

 least from ten to twenty thousand stars, compacted and wedged together in a 

 round space whose visible magnitude is not a tenth part of that of the disk of 

 the moon.* 



One of these objects (the 13th, in Messier's catalogue), is represented in the 

 annexed diagram, fig. 3. 



This, as Sir John Herschel observes, is exhibited by the telescope as con- 

 sisting entirely of stars crowded together so as to present an almost definite 

 outline, and to run up to a blaze of light in the centre, where their condensa- 

 tion is usually greatest. This beautiful object was v first seen by Halley, in 

 1714. It is visible to the naked eye between the stars p and in the constel- 

 lation of Hercules. If an imaginary line be drawn from the star (first magni- 

 tude) a Lyrse, to the star (second magnitude), in the constellation of Hercules, 

 it will pass through this nebula near the latter star. 



In fig. 4, annexed, is exhibited a sketch of one of the most remarkable 

 nebulae in the firmament. This is the 27th in Messier's catalogue. Its form 

 may be likened to an hour-glass, a double-headed shot, or a dumb-bell, surrounded 

 by a thin hazy atmosphere. This belongs to a class of nebulae which show 

 an evident symmetry of form. It consists, according to Sir John Herschel's 

 observations, of two bright and highly-condensed round or rather oval nebulae, 

 united by a short neck of nearly the same density. A faint nebulous atmo- 

 sphere completes the figure, enveloping them both, and filling up the outline 

 of a circumscribing ellipse, whose shorter axis is the symmetrical axis of the 

 system, or the line passing through the centres of both the chief nebulous 

 masses. 



In fig. 5 is presented a nebula of an elliptical form, which is visible to the 

 naked eye. In the latitude of New York it passes near the zenith at about 

 nine o'clock at night in the month of November, and in the following months 

 may be seen in the evenings in the northwest, at a considerable altitude. It 

 appears like a dull, cloudy, undefined spot upon the concave of the firmament, 

 and has sometimes been compared to the light of a small candle seen through 

 horn. Its central parts appear brightest, but its light gradually fades away 

 toward each extremity. A few small stars appear adjacent to it, but they have 

 | no immediate connexion with the nebula. Its length is nearly equal to the 



'Herachel.chap.xii. 



