INTRODUCTION. 



The design of the following Catalogue is to give a full list of 

 books and memoirs relating to Nebulae and Clusters, and to include 

 references to papers on allied subjects — as the Milky Way, the Neb- 

 ular Hypothesis, etc., etc., which may serve to give as complete a 

 knowledge as possible of the first two subjects. It was undertaken 

 in 1874, for my own use, and has been steadily prosecuted until 

 the present time ; and I am induced to offer it for publication, by 

 the hope that it may be found as useful to others as it has already 

 been to myself. It is believed to be nearly complete, so far as the 

 uses of the astronomer require. It is impossible, in a work of this 

 kind, to insure its entire completeness, but it is hoped that few im- 

 portant papers are omitted. It is also beyond the limits of the plan 

 to make an index for the bibliographer chiefly. 



In reading upon any special subject there are several cases which 



may arise : First, having any given series of publications, as the 



Philosophical Transactions, for example, one may wish to know all 



that has been printed in that series on this particular subject. The 



present index has under the title of each publication a reference to 



all works on nebulae and clusters contained in it. Second, one 



may wish to know all the works on the special subject which we 



owe to a particular author no matter where published ; in the 



present index, under each author's name, is given a list of his 



writings on nebulae, etc., arranged not chronologically, as in a 



work of more extended scope they should be, but by periodicals. 



All the papers of D'Arrest, for example, in the Astronomische 



Nachrichten, are to be found together, chronologically arranged, 



and so with papers in other journals. This form is convenient 



for an index of so special a nature as the one in question, par- 



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