Each branch of a curve has its history, but this history does not reach
further back among the nations of the West than the memorable epoch of the
13th of September, 1492, when the re-discoverer of the New World found a
line of no variation 3 degrees west of the meridian of the island of Flores,
one of the Azores.*
[footnote] *I have elsewhere shown that, from the documents which have come
down to us regarding the voyages of Columbus, we can, with much certainty,
fix upon three places 'in the Atlantic line of no declination' for the 13th
of September, 1492, the 21st of May, 1496, and the 16th of August, 1498.
The Atlantic line of no declination at that period ran from northeast to
southwest. It then touched the South American continent a little east of
Cape Codera, while it is not observed to reach that continent on the
northern coast of the Brazils. (Humboldt, 'Examen Critique de l'Hist. de la
Geogr.', t. iii., p. 44-48.) From Gilbert's 'Physiologia Nova de Magnete',
we see plainly (and the fact is very remarkable) that in 1600 the
declination was still null in the region of the Azores, just as it had been
in the time of Columbus (lib. 4, cap. 1). I believe that in my 'Examen
Critique' (t. iii., p. 54) I have proved from documents that the celebrated
line of demarkation by which Pope Alexander VI.
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