INTRODUCTION. V 



the work a finding list of Sir William Herschel's classes and 

 numbers, as well as of Messier's nebulae — the identifications rest 

 ing on the authority of Sir J. Herschel. 



The abstracts of Sir William Herschel's papers I have made 

 much more full than in other cases, in order to present, if possible, 

 something like an adequate idea of the views of this great man on the 

 subject which is peculiarly his own. This is the more necessary, as 

 we have as yet no collection of his works which is generally avail- 

 able, (a want which it is hoped may be filled,) and as the earlier 

 volumes of the Philosophical Transactions are now quite rare.* 



References to translations and reprints of important papers have 

 frequently been included in order that such papers may be accessible 

 to as many as possible in the native language of the reader. 



Many popular and historical papers have been referred to which 

 appeared in Reviews and Magazines, but it is not supposed that such 

 references are by any means exhaustive of this part of the subject, 

 uor does it seem desirable that they should be so, since they are 

 largely repetitions one of another. 



I have included (with some hesitation) a few references to the 

 views of the ancients on the Milky Way, etc., which may be 

 thought to render the Index more complete by presenting more 

 fully the historical side of the subject ; but in the main it refers to 

 publications made between the epoch of the invention of the tele- 

 scope and the present time. 



It is to be noted that the references here made are always from a 

 consultation of the original work, when this was accessible, and not 

 by a transcription from any indices or general catalogues, like the 

 Royal Society's Catalogue of Scientific Papers for example. These 



* A complete collection of his separate papers exists at the Pulkowa 

 Observatory, and also one in five volumes in the possession of his descend- 

 ants in England, but in order to gain an acquaintance with them in general, 

 it is necessary to examine no less than thirty-nine separate volumes of the 

 Philosophical Transactions. Much unpublished and most precious material 

 exists in manuscript. 



