If this be admitted, it will, in a great measure, enable me to find the direction and strength of the currents we met with on this passage from England. For, by comparing the latitude and longitude by dead reckoning with those by observation and the watch, we shall, from time to time, have, very accurately, the error of the ship's reckoning, be the cause what it will. But as all imaginable care was taken in heaving, and keeping the log, and every necessary allowance made for lee-way, heave of the sea, and other such circumstances, I cannot attribute those errors that did happen to any other cause but currents; but more particularly when the error was constantly the same way for several days successively.
On the contrary, if we find the ship a-head of the reckoning on one day, and a-stern of it on another, we have reason to believe that such errors are owing to accidental causes, and not to currents. This seems to have been the case in our passage between England and Teneriffe. But, from the time of our leaving that island, till the 15th of August, being then in the latitude of 12° N. and longitude 24° W. the ship was carried 1° 20' of longitude to the westward of her reckoning. At this station the currents took a contrary direction, and set to E.S.E. at the rate of twelve or fourteen miles a day, or twenty-four hours, till we arrived into the latitude of 5° N. and longitude of 20° W.; which was our most easterly situation after leaving the Cape de Verde Islands till we got to the southward. For in this situation the wind came southerly, and we tacked and stretched to the westward; and, for two or three days, could not find that our reckoning was affected by any current. So that I judged we were between the current that generally, if not constantly, sets to the east upon the coast of Guinea, and that which sets to the west toward the coast of Brazil. This westerly current was not considerable till we got into 2° N. and 25° W. From this station to 3° S. and 30° W. the ship, in the space of four days, was carried 115 miles in the direction of S.W. by W. beyond her reckoning; an error by far too great to have any other cause but a strong current running in the same direction. Nor did its strength abate here; but its course was afterward more westerly, and to the N. of W., and off Cape Augustine N. as I have already mentioned. But this northerly current did not exist at twenty or thirty leagues to the southward of that Cape, nor any other, that I could perceive, in the remaining part of the passage. The little difference we afterward found between the reckoning and observations, might very well happen without the assistance of currents, as will appear by the table of Day's Works.[90]