The most recent editor, Professor Gercke, divides Book IV. into its two constituents, IV. (_a_) = IV. Pref.-ii., IV. (_b_) = IV. iii.-xiii., and arranges the Books in ascending scale thus: Earth III. IV. (_a_); Air IV. (_b_), II. V. VI; Heaven VII. I. There seems great probability, almost amounting to certainty, that there were originally eight Books, as he supposes. But a consistent and fairly natural order might perhaps be restored with less violence to the accepted form than his scheme involves. Books III. and IV. (_a_) seem to have been misplaced or transposed, being placed after Book II. instead of after Book VI., where they originally stood; Book IV. (_a_) had somehow got mutilated, which the more easily led to the confusion. Book IV. (_b_) also suffered somewhat in the process. Thus the original order may have been I. II. IV. (_b_), V. VI.; III. IV. (_a_); VII.; the first five Books deal with Meteorology, including Seismology (air), the next two with Physical Geography (earth), the last Book with Astronomy (heaven). A single change of the order is thus all that is required; but, of course, the regrettable gap after IV. (_a_) remains. Even with this rearrangement the sequence leaves something to be desired. But it must be borne in mind that the author makes a claim to philosophic liberty (178), and that in no case can the rules of modern requirement be applied to him. Of course, if the assumption of methodical arrangement be unfounded, and the author composed just as the humour took him, the existing order may be all right: it is as good as any other fortuitous collocation. Some have supposed that the work was left unfinished at the author’s death, but of this we have no proof. The language of the Preface to Book III. has been taken by some to imply that this was the opening of the whole work. Whether this is so must remain to some extent matter of opinion. It may, however, be pointed out (_a_) that the claim of the Preface to Book I. seems at least equally strong, (_b_) that the language of § 4 of the Preface to Book III. (110), “how much is unaccomplished of my plan, though not of my life,” seems inapplicable to a work that was not begun or merely beginning. There was a remnant of the work and a remnant of life, but they were disproportionate, the one large, the other small. This was a reminder to hurry on to completion a work with which, _ex hypothesi_, some progress had already been made.