The magnetic compass sailed westward for centuries out of China, until even Atlantic mariners used it widely. In the round year of 1600, a prominent physician of Elizabethan London, William Gilbert, authored--in Latin--the first classic of that springtime century of science, under the grand title About Magnets and Magnetic Bodies, and that Great Magnet, the earth,... & demonstrated by experiments. That English rendering is still in print (Dover paperback). No wonder Galileo prized Gilbert's amazing work, 10 years earlier than Galileo's own celebrated Latin classic on the telescopic sky.

Natural magnets, called lodestones, are samples of magnetite, the complex black oxide of iron, and were then chief donors of magnetization. Any piece of smelted iron could be magnetized by stroking it with a good-size lodestone. (The old word "lode" occurs still in the poet's word "lodestar" and carries the sense of leading one on.) Gilbert tells just how to proceed even without a lodestone: ordinary iron metal, "if it be drawn out long" and held in the north-south line, can magnetize compass needles quite well.

This article was originally published with the title Anniversary of Needles.

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