PREFACE TO THE SECOND EDITION I AM Sorry to say that in the first edition there were a very much larger number of typographical and other errors than I had hoped. I wish to tender my sincere thanks to those correspondents who have been so good as to send me lists of errata. In this edition I hope I have corrected all the errors of any importance. W. W. October 1900. PREFACE TO THE THIRD EDITION In this edition some additions have been made to the text where the treatment seemed inadequate, and a set of Examples and Questions, arranged according to the chapters, has been added. It is hoped that the answers are correct, as they have been checked by Mr. W. S. Tucker, to whom the author wishes to express his thanks. Any reader who discovers any mistakes will confer a great favour by sending a note of such errors to the publishers or author. January 1902. W. W. PREFACE TO THE FOURTH EDITION In this edition a number of additions and alterations have been made, rendered necessary in part by discoveries which have been made, or at any rate confirmed, since the book was first published. Further, the use of the book as a text-book, and letters received from a number of teachers and others, have indicated directions in which the exposition might with advantage be altered, and it is hoped that in this way the utility of the book will be enhanced. Although a detailed account of the recent work on radio-activity and the allied subjects is hardly suited to the scope of the work, the main points have been noted, while the chapter on the passage of electricity through gases has been practically re-written. Additions have also been made to the geometrical optics of optical instruments, as experience has shown that it is impossible otherwise to obtain a correct idea of the manner in which such instruments act. The great importance of a correct appreciation of this subject need hardly be insisted on, for the telescope and microscope play an important part in many physical experiments. The insertion of a considerable amount of additional matter has necessitated a slight alteration in the typography, as otherwise the bulk of the book would have been excessive. The author would like to take this opportunity of saying how much he has appreciated the letters offering advice and criticism with which readers, both in England and America, have favoured him. He also hopes that he may continue to hear from those who use the book. April 1905. W. W. PREFACE TO FIFTH EDITION IN this edition various alterations and additions have been made where it seemed desirable, either on account of obscurity in the previous edition or of extensions to our knowledge which have been made during the last few years. For pointing out directions in which the book might be improved the author is much indebted to many teachers and others who have used the book, and he wishes to express his gratitude for help thus given. Recent work on radio-activity has necessitated extensive alterations and additions in the chapter dealing with the passage of electricity through gases. A large number of additional examples and questions have been added; and the author is much indebted to Mr. F. C. Hobbs, who has kindly checked the answers. CONTENTS 7. Fundamental and derived units. 8. Absolute systems of units. 9. Dimensions of derived units. § 15. Importance of length measurements. meter screw. 18. The screw-gauge. |