Page:A Voyage of Discovery and Research in the Southern and Antarctic Regions Vol 1.djvu/17

Rh of heat and cold, depending on the annual and diurnal movements of the sun. The discovery of the affection of the needle by the aurora borealis, and of the existence of minute and irregular movements, which might be referred either to unperceived auroras or to other local and temporary causes, sufficed to show that the laws of terrestrial magnetism are not so simple as to admit of this summary form of expression; and the important discovery, first announced, we believe, by Baron von Humboldt, that those temporary changes take place simultaneously at great distances in point of locality, (a discovery which has since been remarkably confirmed and extended to very great intervals of distance, so as to include the whole extent of the European continent, by Gauss and Weber, and their coadjutors of the German Magnetic Association,) has sufficed to show that the gist of the inquiry lies deeper, and depends upon relations far more complex, while at the same time the dominion of what might previously have been regarded as local agency, would require, in the new views consequent on the establishment of these facts, to be extended far beyond what ordinary usage would authorise as a just application of that epithet.

"For a long time in the history of terrestrial magnetism the variation alone was attended to. The consideration of the dip was then superadded; but the observation of this element being more