A Discourse Mathematical on the Variation of the Magneticall Needle. Together with its admirable Diminution lately discovered

by Henry Gellibrand

$50,000 · Offered by Sophia Rare Books

First edition

London: William Jones, 1635. First edition, extremely rare, of Gellibrand’s most important discovery: the secular change in magnetic declination, or variation. According to William Gilbert in his De Magnete 1600 , the existence of magnetic declination, the difference in direction between geographical and magnetic north, is a result of the magnetic effects of large land masses. This explained the observed

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