The four Essays are reprinted substantially as they were first delivered and published. But verbal errors and actual misquotations have been corrected; and allusions to specimens or diagrams exhibited during the original discourses, but not published, have been replaced so far as possible by references to similar objects figured in the Plates.
The Plates are photographic reproductions of the original illustrations, with the exception of Plates V, XIII, XVII, XVIII. Of these, Plate XIII has simply been re-drawn, from a faded original; Plates XVII and XVIII have been translated, without loss of detail, from colours to monochrome shading; Plate V has been reconstituted from illustrations quoted in the text, with the permission of their publisher, Mr. Murray. Plate XXI is reproduced, by permission of Sir John Evans, from the paper which it illustrated originally.
The footnotes demand a word of explanation. The author, as the original publications show, was not precise in indicating his sources: he frequently gave, as a quotation, the general sense rather than the exact words of his authority; and occasionally his memory played him false. In the reprint, the precise references have been identified, and are given in full, and obvious errors in the text have been either amended or corrected in a footnote. The editor desires to acknowledge much valuable help in the search for references from Miss C. M. Prior, of Headington.