In northern latitudes the trade wind blows from north-east, or varies but a few points from that direction.

South of the equator it blows constantly from the south-east; and the "south-east trade" is more steady than the trade wind north of the line.
It often happens that vessels bound to the United States from India, after passing the Cape of Good Hope, steer a course nearly north-west, carrying studding-sails on both sides, uninterruptedly, through fifteen or twenty degrees of latitude.
The cause of the trade winds is supposed to be the joint influence of the higher temperature of the torrid zone and the rotation of the earth on its axis.

On the equator, and extending sometimes a few degrees on either side, is a tract where light easterly winds, calms, and squalls, with thunder, lightning, and inundating rains, prevail.
From what I have said, it will be seen that vessels bound from the American coast to the West Indies or Guiana should steer to the eastward in the early part of their passage, while they have the advantage of variable winds.

And this precaution is the more important, as these vessels, being generally dull sailers and deeply laden, will fail to reach their port if they fall to leeward, unless by returning north into the latitude of the variable winds, and making another trial, with the benefit of more experience.
In those days there were no chronometers in use, and but few of our West India captains were in possession of a sextant, or indeed able to work a lunar observation.

The latitude was accurately determined every day by measuring the altitude of the sun as it passed the meridian.