Say, for instance, you are bound for Calcutta. The first of the
north-east trades will give a fair idea of your latitude being
about the edge of the tropics somewhere, or say from 20deg. to
25deg. N., whether you have sighted any of the islands or not.
Then away you go before the wind down towards the Equator, the
approach to which is notified by the loss of the trade and the
dirty, changeable weather of the "doldrums." That weary bit of
work over, along come the south-east trades, making you brace
"sharp up," and sometimes driving you uncomfortably near the
Brazilian coast. Presently more "doldrums," with a good deal
more wind in them than in the "wariables" of the line latitude.
The brave "westerly" will come along by-and-by and release you,
and, with a staggering press of sail carried to the reliable
gale, away you go for the long stretch of a hundred degrees or so
eastward. You will very likely sight Tristan d'Acunha or Gough
lsland; but, if not, the course will keep you fairly well
informed of your longitude, since most ships make more or less of
a great circle track. Instead of steering due East for the whole
distance, they make for some southerly latitude by running along
the arc of a great circle, THEN run due east for a thousand miles
or so before gradually working north again.
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