Third Edition, Revised. London, "The Electrician" Printing Co, 1900. 443 p.During recent years, and especially during the last ten, our knowledge of the physical facts of Magnetisation has made a marked advance. Perhaps no subject has profited more by the beneficent reaction of Practice on Science. The labours of a number of observers have made it possible to present a connected account of the phenomena of magnetic induction and of the distinctive qualities of the magnetic family of metals. There are still, of course, many questions for experiment to answer ; but a text-book of the subject may now be written with some degree of continuity and completeness.In attempting this task, the author has not approached the matter from the standpoint of the scientific historian. He has been more concerned to tell of things discovered than of discoverers. In many instances, therefore, the work of early observers is passed over with no rriention, or with the briefest, because later experiments are found to deal with the same points in a more conclusive or more exhaustive way.The author's aim has been to present the subject in sufficient detail to satisfy scientific students, as well as to meet the wants of those who may turn to the book in quest of data for application -to matters of practice. Particulars, which will facilitate reference to the original memoirs in which researches are described, have in all cases been given for the assistance of those who may wish to pursue the subject further than a short text-book can well take them.After an introductory chapter, which attempts to explain the fundamental ideas and the terminology, an account is given of the methods which are usually employed to measure the magnetic qualities of metals. Examples are then quoted, showing the results of such measurements for various specimens of iron, steel, nickel, and cobalt. A chapter on Magnetic Hysteresis follows, and then the distinctive features of induction by very weak and by very strong magnetic forces are separately described, with further description of experimental methods, and with additional numerical results. The influence of Temperature and the influence of Stress are next discussed. The conception of the Magnetic Circuit is then explained, and some account is given of experiments which are best elucidated by making use of this essentially modern method of treatment. The book concludes with a chapter on the Molecular Theory of Magnetic Induction ; and the opportunity is taken to refer to a number of miscellaneous experimental facts, on which the molecular theory has an evident bearing.Throughout the book the author has endeavoured to familiarise the student with the notion of intensity of magnetisation (|) as well as with the notion of magnetic induction (B). It has been urged by some writers that the alternative which is in this way offered is unnecessary and confusing, and that if we keep "B" we may dispense with " I. " The scientific value and the practical utility of " B " are so obvious that no one proposes to avoid using that. It is " | " that we are told must go. In this cry the author is by no means disposed to join. It is not too much to say that in stating the magnetic qualities of a metal the quantity " | " is of primary importance. The facts of saturation, the molecular theory, and the phenomena of magneto-optics, all demonstrate its physical reality and its fundamental interest.The author would take this opportunity to repeat an acknowledgment, already made elsewhere, of the assistance most willingly and ably rendered by a number of his pupils in carrying out experiments on some of the subjects with which this book deals. Messrs. Tanakadate, Fujisawa, Tanaka, and Sakai, in Japan, and Messrs. W. Low, Cowan, D. Low, and Frew, in Dundee, have been skilful and sympathetic collaborators, whose interest was as lively as their patience was inexhaustible.A reminder of how far the subject still is from finality comes, as the last pages are passing through the press, in the announcement by Prof J. J. Thomson of his demonstration that iron continues to be strongly susceptible to magnetisation by such rapid alternations of magnetic force as occur in a Ley den- jar discharge; and that the damping-out of the electric oscillations when the discharge traverses a coil with an iron core proves magnetic hysteresis to play an important part, notwithstanding the excessive frequency of the reversals. Independent Experiments made by Prof Trowbridge point to the same conclusion. Prof Thomson's use of vacuum-globes without electrodes as induction secondaries opens up new possibilities of magnetic research, which he has himself been the first to turn to account.PREFACE TO THE THIRD EDITION
In this Edition a number of references are given to advances which the subject has made since the book was originally published, and a Chapter is added on " Practical Magnetic Testing. "
