a sailor who makes the same voyage
every year, but not precisely at the same time each year (and it must be
remembered that the rigid punctuality at starting which now holds good
did not exist in former times). In his first voyage he had to cross,
say, four of the wind-belts. While crossing belt number one, he
experiences south-west winds chiefly, and, being an observant man, notes
the fact. In belt number two he encounters westerly winds. In number
three he is in a region of variable winds and calms. In this region the
winds blow all round the compass, averaging about three months from each
quarter. But our sailor does not know that; he does not stay there all
the year to make notes; he passes on, having recorded his experience.
In crossing belt number four, he finds the prevailing winds to be
easterly.

Next year he sets forth again but merchants are not always punctual.
The lading cannot be completed in time, or adverse winds render the
setting sail unadvisable. At length, after a month or six weeks' delay,
he proceeds on his voyage, and finds belt number one perhaps much the
same as last year. He congratulates himself on his good fortune, and
notes his observations; but in belt number two, the wind is somewhat
modified, owing to its being later in the season,--it is rather against
him. In number three it is right in his teeth, whereas last year it was
quite in his favour. In number four, which we will suppose is the
trade-wind belt (of which more hereafter), he finds the wind still
easterly. Here, then, is the groundwork of confusion in our sailor's
mind. He has not the remotest idea that in belt number one the wind
blows chiefly, but not always, in one particular direction; that in
number four it blows invariably in one way; and that in number three it
is regularly irregular. In fact, he does not know that such belts exist
at all, and his opportunities of observing are not sufficiently frequent
or prolonged to enable him to ascertain anything with certainty.

Now, when we remember that in this imperfect experience of his he is
still further misled by his frequently encountering _local_
vicissitudes--such as storms and calms resulting from local and
temporary causes--we see how confusion becomes worse confounded. No
doubt he does gather some few crumbs of knowledge; but he is called on,
perhaps, to change his scene of action. Another ship is given to him,
another route entered on, and he ceases alto