In our passage to the island of St Catharines, we found the direction of the trade winds to differ considerably from what we had reason to expect, both from the general histories given of these winds, and the experience of former navigators. For the learned Dr Halley, in his account of the trade-winds which prevail in the Ethiopic and Atlantic Oceans, tells us that, from the lat. of 28 deg. N. to 10 deg. N. there is generally a fresh gale of N.E. wind, which, towards the African coasts, rarely comes to the eastward of E.N.E. or passes to the northward of N.N.E. but on the American side the wind is somewhat more easterly; though even there it is commonly a point or two to the northward of east; that from 10 deg. N. to 4 deg. N. the calms and tornadoes take place; and from 4 deg. N. to 30 deg. S. the winds are generally and perpetually between the south and east. We expected to find this account of the matter confirmed by our experience; but we found considerable variations from it, both in regard to the steadiness of the winds, and the quarters from whence they blew. For though we met with a N.E. wind about lat. 28 deg. N. yet, from lat. 25 deg. N. to 18 deg. N the wind was never once to the northward of E. but almost constantly to the southward of it. From thence, however, to 6 deg. 20’ N. we had it usually to the northward of E. though not always, as it changed for a short time to E.S.E. From 6 deg. 20’ N. to about 4 deg. 46’ N. the weather was very unsettled, the wind being sometimes N.E. then changing to S.E. and sometimes we had a dead calm, with small rain and lightning. After this, to the lat. of 7 deg. 30’ S. the wind continued almost invariably between S. and E. and then again as invariably between N. and E. till we came to 15 deg. 30’ S. then E. and S.E. to 21 deg. 37’ S. After this, even to 27 deg. 44’ S. the wind was never once between S. and E. though we had it in all the other quarters of the compass; though this last circumstance may be in some measure accounted for from our approach to the coast of Brazil.
I do not mention these particulars with a view of cavilling at the received accounts of these trade-winds, which, I doubt not, are sufficiently accurate; but I thought it worthy of public notice, that such deviations from the established rules do sometimes take place. This observation may not only be of service to navigators, by putting them on their guard against these hitherto unexplained and unnoticed irregularities, but it is also a circumstance that requires to be attended to in the solution of the great question about the causes of trade-winds and monsoons; a question which, in my opinion, has not been hitherto discussed with that clearness and accuracy which its importance demands, whether it be considered in a naval or a philosophical point of view.