Note 432 — TREATISE OF NAVIGATION OF THE CHEVALIER ANTONY PIGAFETTA.
Henry Edward John Stanley Stanley translation
Amoretti, in his introduction to this Treatise of Navigation, in the Milan edition, observes that Pigafetta was misled by a false theory when he supposes that there is in the heavens a point in repose to which the magnetic needle tends, but that the exact direction of the magnetic needle coincided, or at least approximated, to the meridian of the isle of Ferro, which is not now the case; and that in some other places the variations of the compass had been observed to correspond with that of the longitude. By the table of variations of the compass published by Lambert in the Ephemerides of Berlin (Astronomische Jahrbuch) for the year 1779, it is seen by an easy calculation that at the beginning of the sixteenth century the magnetic equator or zero of deviation was very near the isle of Tenerife. Now it is further off, and the distance increases. M. de Bougainville found there the deviation to the west to be 14 deg. 41 min.; and Staunton, the companion of Lord Macartney, found it to be 17 deg. 35 min.