PREFACE.

Although I had long purposed to draw up a treatiseon the Moon , to form part of the series of volumes towhich my works on Saturn and the Sun appertain, Ioriginally proposed that this treatise should be thelast instead of the third of that series. But Mr.Brothers being desirous of publishing three of Mr.Rutherfurd’s magnificent lunar photographs, asked meto prepare some accompanying letterpress, and thepresent work thus had its origin; for I soon foundthat if I supplied the required quantity of letterpress,I should to some extent injure the prospects of themore complete work which I had in view. Moreover,it seemed to me desirable not to take up the subjectpartially and resume it at some distant epoch, but todeal with it in a single effort. This will serve toexplain the delay which ensued ; for certain parts ofmy subject-matter required much time and closeapplication, for their thorough and independent in-vestigation. I ought also (for reasons which willbe understood by subscribers to the large volume) toexplain that Mr. Brothers and I found it convenientto separate our interests; so that while I provide