Thus, in his work on the Round Towers, Dr. Petrie assigned "about the year 1020" as the date of the round tower of Brechin, but in one of the notes he corrects himself, and explains the origin of his mistake:--"The recollection of the error which I made, by a carelessness not in such matters usual with me, in assigning this date 1020, instead of between the years 971 and 994, as I ought to have done, has long given me annoyance, and a lesson never to trust to memory in dates; for it was thus I fell into the mistake. I had the year 1020 on my mind, which is the year assigned by Pinkerton for the writing of the _Chron. Pictorum_, and, without stopping to remember or to refer, I took it for granted that it was the year of Kenneth's death, or rather of his gift." In writing of the Early Churches or Oratories of Ireland, Dr. Petrie stated in his Essay--"they had a single doorway always placed in the centre of the west wall." In one of his notes, now printed, he thus qualifies the statement:--"I should perhaps have written _almost_ always. The very few exceptions did not at the moment occur to me." Again, Sir James Simpson having quoted a passage from Dr. Petrie's work, in which the writer ascribes the old small stone-roofed church at Killaloe to the seventh century, Dr. Petrie, in his relative note, adds--"but now considers as of the tenth, or perhaps eleventh." To the paper on "Leprosy and Leper Hospitals in Scotland and England" is now added a series of additional "Historical Notices," prepared by Dr. Joseph Robertson, with the accuracy and research for which, as is well known, my early friend was conspicuous. The origin of the tract on "Medical Officers in the Roman Army" is explained in the following note, prefixed to the first edition:--"A few years ago my late colleague, Sir George Ballingall, asked me--'Was the Roman Army provided with Medical Officers?' He was interested in the subject as Professor of Military Surgery, and told me that he had made, quite unsuccessfully, inquiries on the matter in various quarters, and at various persons. I drew up for him a few remarks, which were privately printed and circulated among his class at the time. The present essay consists of an extension of these remarks." The essay on the monument called "THE CATSTANE" suggested an explanation, which naturally elicited divergent criticisms. Some of these appear to have occasionally engaged Sir James Simpson's attention; and from some unfinished notes among his papers, it seems plain that he meant to notice them in an additional communication to the Society of Antiquaries.