Chapters in the History of Terrestrial Magnetism

1--The science of Terrestrial Magnetism is based on the fact that a magnet, free to move about its center of gravity, tends to assume a position of relative rest in an approximately definite direction with respect to the geographical meridian and the vertical at the place of observation. That it should do so must be due to the existence of a field of force which is known as the terrestrial magnetic field [1], and the systematized knowledge of that field, of its variations in time and space, and of its relations with the subject-matter of other branches of terrestrial and cosmical physics, constitutes the science of Terrestrial Magnetism. The object of these articles is to present a history, as complete as possible, of the development of this science. The method adopted will be that of collating the various accounts which have been given of the discovery of its fundamental principles and their gradual evolution into the form in which they are at present held. To assist the reader in forming his own conclusions, an attempt has been made to provide ample bibliographical references. 2--The first matter which arises for consideration in the history of the science is that relating to the discovery of the directire property of a magnet with reference to the Earth. By whom, at what date, and in what form, this was first recognized is now unknown, for the discovery was made in times long before the maintenance of careful scientific record. The investigation of this question has given rise to an extensive literature, but has led to few conclusions of a definite kind. Its treatment in standard works on magnetism is generally--and necessarily--confined to a brief statement which does not profess to be critical or discriminative, and for an adequate understanding of its many difficulties and obscurities we must examine the writings of those who have dealt with one or other of its numerous aspects. The matter practically reinlyes itself into an enquiry as to the origin or invention of the madner's compass, and to the honor of this discovery several claims have been advanced.