The Earth's Magnetism

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Excerpt from The Earth's Magnetism: Delivered in the Schools of the University of Oxford, May 22nd, 1913 According to the regulations governing this lecture, it is to be known as the Halley Lecture on Astronomy and Terrestrial Magnetism. Astronomy shall include Astrophysics, and Terres trial Magnetism shall include the physics of the external and internal parts of the terrestrial globe. This lecture might, therefore, with propriety cover the whole range of investigation in terrestrial and cosmical magnetism. However, we must limit ourselves to those particular lines of research in our subject in which Halley himself was chie¿y interested. It so happens that these are the very lines also in which I have been given the opportunity to continue and expand the work begun by him. After Halley had made two attempts to establish a working theory respecting the distribution of terrestrial magnetism and the cause of its striking change with the lapse of years - the so-called secular variation - he must have reached the conclusion that the elusive problem of the Earth's magnetism would be more profitably advanced by additional facts than by further speculation. That, paraphrasing Seneca, to avoid making a false calculation of matters, it were better to advise with Nature rather than with opinion. Accordingly we find him setting out in October, 1698, in command of a sailing ship, the Paramour Pink, and cruising in her under orders from the British Government, back and forth, north and south, in the Atlantic Ocean for two years, observing almost daily, sometimes several times in a day, the angle which the compass needle makes with the true north and south line - the angle known to the man of science as the magnetic declination, to the mariner and surveyor as the variation of the compass. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully, any imperfections that remain are intentionally left to preserve the state of such historical works.