Besides the difficulty there is in obtaining the exact rate and direction of a current, it is known that a continuance of the wind in any particular quarter may so far change its rate of moving, and even its direction, that at another time it may be found materially different in both.  Of the probability of these changes the commander of a ship must form his own judgment, from the winds he may have previously experienced; and he will consider what is here said upon both winds and currents, as calculated and intended to give him a general notion, and no more, of what may usually be expected upon the South Coast.

(Atlas Plate I.)

Several days before making Cape Leeuwin, I experienced a current setting to the northward, at the rate of twenty-seven miles per day; but at the mean distance of forty leagues, west-south-west from the cape, the current ran north-east, twenty-two miles; and when the ship got in with the South Coast, I found it setting N. 70 deg.  E., at the average rate of twenty-seven miles per day:  this was in the month of December.  On approaching Cape Leeuwin in May, from the north-westward, the current for five days was ten miles to the east; but at forty leagues from the cape, it ran N. 35 deg.  E. fifteen miles; and from the meridian of the cape to past King George’s Sound, the current set east, twenty-seven miles per day, nearly as it had before done in December.  Captain Vancouver and admiral D’Entrecasteaux do not speak very explicitly as to the currents; but it may be gathered from both, that they also experienced a set to the eastward along this part of the South Coast.

The winds seem to blow pretty generally from the westward at Cape Leeuwin.  In the summer time, they vary from north-west in the night, to south-west in the latter part of the day, though not regularly; and in the winter season this variation does not seem to take place.  A long swell of the sea, called ground swell to distinguish it from the lesser, variable one of the surface, appears to come at all times from the south-westward, which indicates that the strongest and most durable winds blow from that quarter; and this was partly confirmed by our experience, for whenever it blew hard, the wind was at, or near to south-west.

It is from the superior strength and apparent prevalence of this wind, that the currents in the neighbourhood of Cape Leeuwin may be explained.  The sea being driven in from the south-west, and meeting with the cape, will necessarily be divided by it, and form two currents, which will follow the directions of the land; one branch will run northward, along the west coast of Terra Australis, and the other eastward along the South Coast:  our present business is to follow the latter current.