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the numerous phænomena of terrestrial magnetism, with which we can only become acquainted by continued observations, accurately performed at various points of the earth's surface, none are in need of a more rigorously systematized cooperation of observers, than the irregular variations to which we find this force to be subject. It is sufficiently well known that the Variation, the Dip, and without doubt the Intensity also, (although with respect to the latter, which has but recently been admitted into the circle of inquiries, sufficient observations are still wanting) continually undergo changes—secular changes, which attract our attention only after long intervals of time, but which eventually become very considerable,—and periodical changes, varying according to the yearly and daily period. But for these regular changes, a rigorously systematized cooperation of observers, at various stations, is not essentially necessary, although highly desirable for the purpose of hastening the extension of our knowledge; in these points, every observer, even independently of others, may contribute useful additions.

Such, however, is not the case with respect to the irregular variations to which only of late years a larger share of attention has been devoted. Hiorter and Celsius observed, nearly a century ago, that during the appearance of an aurora borealis, the magnetic needle undergoes irregular and, frequently, very great oscillations; and this was subsequently confirmed by numerous observations made by others. Hence it might have been concluded, that the same forces which produce the phænomenon of an aurora borealis act also at the same time upon the magnetic needle; and further, that this action must extend to very considerable distances, since the northern lights are generally visible over a wide circuit. We obtain a still greater notion of the wide extension