In consequence of misapprehensions into which several of our critics have fallen, we have prefixed to this edition an Introduction wherein the objects of our work, and the mode in which we seek to attain them, are fully but compactly explained. We need therefore say nothing on these matters here. The work has been greatly enlarged, and in many parts almost rewritten; but we have nowhere found it necessary to alter or recall any of the statements hitherto made by us. As we now give our names, we can at length complain of the conduct of a London ‘Weekly,’ which, only a few days after the first appearance of our book, took the (we hope) very unusual course of stating the authorship as a matter of absolute fact, not of conjecture. It was, of course, not authorised to do so, either by ourselves or by our Publisher:—and we regret to find that the exigencies of competition for public favour can be thought capable of justifying, in the eyes of any one, such a course of conduct. As Professors of Natural Philosophy we have one sad remark to make. The great majority of our critics have exhibited almost absolute ignorance as to the proper use of the term _Force_, which has had one, and only one, definite scientific sense since the publication of the _Principia_. As such men are usually among the exceptionally well educated, ignorance of this important question must be all but universal. In addition to what we have said on the subject in the text (§ 97), we would now only mention that the sole recorded case of true Persistency or Indestructibility of Force which we recollect having ever met with, occurs in connection with Baron Munchausen’s remarkable descent from the moon. It is, no doubt, a very striking case; but it is apparently unique, and it was not subjected to scientific scrutiny. B. STEWART. P. G. TAIT. _April 1876._ TABLE OF CONTENTS. Page INTRODUCTION, 1 CHAPTER I. INTRODUCTORY SKETCH. Article Object of the Book, 1 22 Two classes of speculators, 2 24 Why doubters of immortality have lately increased, 3 26 _Belief of the Ancient Egyptians_— Separation between priests and people, 4 26 The abode of the dead, 5 27 Transmigration of souls, 6 28 Embalming of the body, 7 28