In bringing out the First Volume of my edition of Cicero's De Natura Deorum, I have to return my best thanks to the Syndics of the University Press for having undertaken its publication, and both to them and to Mr J. H. Swainson, late Fellow of Trinity College, Cambridge, for the use of the collations of various English MSS. made by the latter, and placed by him in the hands of the Syndicate; also to Mr Samuel Allen of Dublin for the loan of two valuable MSS., an account of which is given in the fifth section of my Introduction. I have further to acknowledge with my hearty thanks the assistance received from friends who have looked over portions of the proof-sheets, as they were passing through the press, especially to my brother, the Rev. John E. B. Mayor, Professor of Latin at Cambridge, and to my former pupil, Mr H. P. Richards, now Fellow and Tutor of Wadham College, Oxford; but above all to Mr J. S. Reid, whose name is well known to scholars from his excellent editions of the Academica and other works of Cicero, and to my old and valued friend Mr H. J. Roby. The help which I have received from the two latter is only imperfectly represented by the additions and corrections marked with the signature R., in the case of those supplied by Mr Roby, and J. S. R., in the case of those supplied by Mr Reid. Many of my own notes have been modified, and perhaps more should have been, in deference to their candid and searching criticism.