Abstract
The study of the Nebulæ has, within the last quarter of a century, attracted much more of the attention of observers than heretofore—as well on account of the singularity of the phenomena presented by many of these objects, as in consequence of the increased optical power of the telescopes which the skill and industry of modern inventors and artists have placed within their reach. The brighter nebulæ cannot be viewed to any advantage, and the fainter cannot he seen at all, except by the aid of telescopes of large aperture; and, thanks to the exertions of Lord Rosse, Mr. Lassell, Messrs. Nasmyth and De la Rue in England, and Messrs. Steinheil, Foucault, and Porro in Germany and France, as regards reflecting telescopes, and to those of Fraunhofer, Merz, Cauchoix, Clarke, Cook, Secretan, Ross, and Dallmeyer as regards refractors; instruments of abundantly sufficient optical capacity not only to repeat and verify the earlier observations, but to disclose new and more interesting features in many cases, have now come into the hands of many observers, both professional astronomers and amateurs, and may be had by any one who is willing to incur a cost which may be considered moderate when it is remembered that instruments of similar dimensions and goodness could not be obtained fifty years ago at any price. In consequence we find a continually increasing attention directed to this department of astronomy. Not to insist on the observations of the Earl of Rosse and Mr. Lassell with their transcendent reflectors, we find a systematic examination and review of them undertaken by M. D'Arrest in the year 1855, by the aid of a refractor of 6-feet focal length and 4½ inches aperture in the Leipzig Observatory, whose results, consisting in the carefully determined places, by repeated observations, of about 230 nebulæ, were published in 1856, in a work entitled “Resultate aus Beobachtungen der Nebelflecken und Stemhaufen” (Erste Reihe, Leipzig). This review has since been carried on by the same excellent astronomer, with the great refractor by Merz of 11 inches in aperture and 16-feet focus, erected in the year 1861 at the Royal Observatory of Copenhagen. Again, from the Observatory of the Collegio Romano, under the direction of Signor Secchi, have emanated many valuable observations, and from that at Harvard College, Cambridge, U. S., under the late and present Professors Rond, some of the most striking pictorial representations of particular nebulæ which we possess. Neither ought a short but very valuable memoir by the late E. Mason, printed in the 7th volume of the Memoirs of the American Academy of Arts and Sciences, to be passed in silence; containing as it does a very elaborate and minute examination, and some excellent delineations of several highly interesting nebulae, particularly those in the great nebulous region of Cygnus. To M. Auwers also we owe many accurate and valuable observations, besides a Catalogue comprising the whole series of Sir William Herschel’s nebulæ arranged in order of right ascension and reduced to a common epoch, of which more hereafter. Should the efforts which are now making to procure for the University of Melbourne in Australia a reflector of the first magnitude prove, as is to be hoped, successful, it is understood that one of the principal uses to which it will be devoted will be the examination and exact delineation of the numerous and wonderful objects of this class which the southern hemisphere presents. These circumstances, but more especially the last-mentioned, render it extremely desirable to have presented in one work, without the necessity of turning over many volumes, a general catalogue of all the nebulæ and clusters of stars actually known, both northern and southern, arranged in order of right ascension and reduced to a common and sufficiently advanced epoch which may serve as a general index to them, and enable an observer at once to turn his instrument on any one of them, as well as to put it in his power immediately to ascertain whether any object of this nature which he may encounter in his observations is new, or should be set down as one previously observed. For want of such a general catalogue, in fact, a great many nebulæ have been, from time to time, in the ‘Astronomische Nachrichten’ and elsewhere, introduced to the world as new discoveries, which have since been identified with nebulæ already described and well known. Many a supposed comet, too, would have been recognized at once as a nebula, had such a general catalogue been at hand, and much valuable time been thus saved to their observers in looking out for them again.