On the variable intensity of ter­restrial magnetism, and the influence of the aurora borealis upon it

• Published in: Abstracts of the Papers Printed in the Philosophical Transactions of the Royal Society of London
• Format: Article in Journal/Newspaper
• Language: English
• Published: The Royal Society 1837
• Subjects: South Pole; North Pole; The Needle; aurora borealis; South pole
• Online Access: http://dx.doi.org/10.1098/rspl.1830.0016; https://royalsocietypublishing.org/doi/pdf/10.1098/rspl.1830.0016

The author gives the results of a series of observations on the vibrations of the magnetic needle, which he undertook last summer, for the purpose of ascertaining whether the intensity of its directive force is affected by the changes in the earth’s distance from the sun, or by its declination with respect to the plane of its equator. He observed that the magnetic intensity is subject to frequent variations, which are sometimes sudden, and of short duration. These anomalies he has been unable to refer to any obvious cause, except when they were accompanied by the appearance of the aurora borealis, which evidently affected the needle on many occasions. He also thinks that the vibrations of the needle became less rapid with a moist atmosphere, and more so when it was very dry. Changes of the wind and snow storms appeared also to be attended with fluc­tuations in the intensity of the magnetism. He endeavoured to ascertain whether there existed any decided and constant difference in the directive force of each pole; conceiving that, on the hypothesis of a central magnetic force, the north pole of the magnet would, in these northern latitudes, be acted upon with much greater energy than the south pole. From his observing that the relative intensity of the two poles is not always the same, he infers the probability of the earth’s magnetism being derived from the agency of electric currents existing under its surface as well as above it, and that the rapid fluctuations in its intensity are owing to meteorological changes. The author is led to conclude that the aurora borealis is an elec­trical phenomenon, and that it usually moves during the night nearly from north to south, and in an opposite direction during the day that it is of the nature of positive electricity; and that its elevation above the earth is much greater than a thousand, and perhaps thou­sands of miles.