"Since the magnetic pointer does not always regard the same northern spot in every locality, but usually varies therefrom, either to the east or to the west, tho' it nevertheless hath and holds ever the same variation in the same place, wherever that may be; it has come about that by means of this variation (as it is called) closely observed and noted in certain maritime regions, together with an observation of the latitude, the same places can afterward be found by navigators when they approach and come near to the same variation. ...Thanks to this magnetic indication, that ancient geographical problem, how to discover the longitude, would seem to be on the way to a solution."