On the Magnet

place of the north point, but generally declines from it either to the east or to the west; yet it always has the same declination in the same place (whatever that might be), and preserves it constantly; it has come about that from that declination (which they call variation), diligently noted and observed in any maritime places, those same places could afterward be found even by navigators from their approach and arrival at the same variation (with the observation of latitude added). Hence, for the Portuguese, in their voyages to the East Indies, there were most certain signs of their approach to the Cape of Good Hope, as is evident from the accounts of Hugo van Linschoten and our most learned Richard Hakluyt; hence also, many of our own skilled captains, sailing from the Gulf of Mexico to the Azores islands, recognized that they had arrived as close as possible to the same; although from their sea charts, they seemed to be six hundred British miles away from them. And thus, by the benefit of this magnetic indicator, that geographical problem concerning the finding of longitude, which for so many centuries has exercised the minds of the most learned mathematicians, might seem in some way satisfied; because once the variation of any maritime place is known, the same could thereafter be found very easily whenever there is need (with the latitude of the same place not unknown).

However, some inconvenience and hindrance seems to be joined to the observation of this variation; because it can only be observed when the sun or stars are shining. Therefore, this magnetic Mercury of the sea, to be preferred by far to Neptune himself and all the gods and goddesses of the sea, continued to bless all sailors: it not only shows the direction in a dark night and cloudy sky, but also seems to bear with it the most certain signs of latitude. For an iron indicator, suspended freely in equilibrium upon its axis by the most subtle artifice (like a balance) and then touched and excited by a magnet, descends to a certain and definite point under the horizon (as in our latitude of London to the seventy-second degree, nearly) in which it finally rests. But under the equator itself, from that admirable agreement and congruence which intercedes between the Earth itself and the terrella a spherical magnet (that is, a spherical magnet) in all and almost every magnetic experiment, it seems very probable indeed (to say the least) that the same indicator (even when rubbed with a magnet) will remain in the equilibrium of the Horizon: from which it is also evident that it is most likely that in a very small progression from the south to the north (or vice versa), the mutation of that declination will be sufficiently sensible; so that from that declination, once diligently observed in any place together with the latitude, the same place, and the same