MAGNETIC PHENOMENA AN ELEMENTARY TREATISE BY SAMUEL ROBINSON WILLIAMS, PH. D., D. Sc. Professor of Ph ys ics, AmKefsl College FIRST EDITION McGRAW-HILL BOOK COMPANY, INC. NEW YORK AND LONDON 1931 COPYRIGHT, 1931, BY THE McGRAW-HiLL BOOK COMPANY, INC. PRINTED IN THE UNITED STATES OF AMERICA All rights reserved. This book, or parts thereof, may not be reproduced in any form without permission of the publishers. THE MAPLE PRESS COMPANY, YORK, PA. The precise derivation of the term magnet, 7 which has now become the most common one, is difficult to ascertain. Lucretius 9955 B. C. says it was called magnet from the place from which it was obtained in the native hills of the Magnesians. However, Pliny 23-79 A. I. relates a prettier legend, as copied from the poet Nicander second century B. C., that the shepherd, Magries byname, while guarding his flock on the slopes of Mount Ida, suddenly found the iron crook of his staff clinging to a stone, which has become known after him as the - Magnes stone or magnet. BATTKK, Principal Facts of the Earths Magnetism. TO MY WIFE WHOSE HELP AND LOYALTY MADE THIS BOOK POSSIBLE FOREWORD The experience of twenty years of undergraduate teaching has shown that college students may be successfully introduced to research work. If the rising generation is to play a leading part in the program of scientific research, much more attention must be paid in the future to arousing the interest of undergraduates in the various fields of science and to inspiring them with the spirit of research. The professions which college men and women follow when they leave college are to a large extent determined by the kind of work that has stimulated them in their undergraduate days. All will agree that the greatest stimulus a student may have for productive scholarship is a teacher wide awake and enthusi astic for his subject, inspiring his students to ask all sorts of questions about the problem in hand. Buch a teacher must himself be filled with a desire to extend his own field of knowledge by study and research. One engaged in research will, in general, make a better teacher and, on the other hand, teaching reacts favorably on the research work. The next great stimulus to scholarship is a good book. Many a student owes his inspiration to the suggestions offered by a book which he has chanced to read. Naturally, the embryo researcher is often found asking the question What and how shall I investigate lie must needs be introduced to those fields which are so alluring to the older investigator and be led to select some subject which will appeal to him. Not only must he be oriented in a given subject but he must become acquainted with the various types of technique necessary to do the work. It is here that the successful teacher or book finds his or its opportunity. While the subject of magnetism is a very old one, it still remains the least understood and also the most neglected of subjects. The investigators who have devoted their lives to this field are few in number. The great trouble with the research work in magnetism is that too many indulge themselves in some problem for a year or two and then drop it for work in other fields. They have developed no background for magnetic X FOREWORD investigations and are, therefore, not able to see the specific problem in its relations to the general field. This book is written in the hope that some youthful adventurer in the field of physics may be induced to choose some phase of the subject of magnetism as a life interest. It is desired that in the course of the succeeding chapters it may be pointed out how many problems are urgently calling for a solution. There is a hope that a beginning in the methods and technique of such investigations may be disclosed as the various subjects are presented, and the novitiate led to try some of the problems himself...