But
what was most shocking to me, I found that the variation did not always
increase or decrease in proportion to the degrees of longitude east or
west; as I had a notion they might do to a certain number of degrees of
variation east or west, at such or such particular meridians. But,
finding in this voyage that the difference of variation did not bear a
regular proportion to the difference of longitude, I was much pleased to
see it thus observed in a scheme shown me after my return home, wherein
are represented the several variations in the Atlantic Sea, on both sides
of the equator, and there the line of no variation in that sea is not a
meridian line, but goes very oblique, as do those also which show the
increase of variation on each side of it. In that chart there is so large
an advance made as well towards the accounting for those seemingly
irregular increases and decreases of variation towards the south-east
coast of America as towards the fixing a general scheme or system of the
variation everywhere, which would be of such great use in navigation,
that I cannot but hope that the ingenious author, Captain Halley, who to
his profound skill in all theories of these kinds, hath added and is
adding continually personal experiments, will e'er long oblige the world
with a fuller discovery of the course of the variation, which hath
hitherto been a secret.
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