It has been found, both by us and the Dolphin, that the trade-wind, in these parts, does not extend farther to the south than twenty degrees, beyond which, we generally found a gale from the westward; and it is reasonable to suppose, that when these winds blow strong, they will drive back the easterly wind, and consequently encroach upon the limits within which they constantly blow, and thus necessarily produce variable winds, as either happens to prevail, and a south-westerly swell. This supposition is the more probable, as it is well known that the trade-winds blow but faintly for some distance within their limits, and therefore may be more easily stopped or repelled by a wind in the contrary direction: It is also well known, that the limits of the trade-winds vary not only at different seasons of the year, but sometimes at the same season, in different years. There is therefore no reason to suppose that south-westerly winds, within these limits, are caused by the vicinity of large tracts of land, especially as they are always accompanied with a large swell, in the same direction in which they blow; and we find a much greater surf beating upon the shores of the south-west side of the islands that are situated just within the limits of the trade-wind, than upon any other part of them. The tides about these islands are perhaps as inconsiderable as in any part of the world. A south or S. by W. moon makes high water in the bay of Matavai at Otaheite; but the water very seldom rises perpendicularly above ten or twelve inches. The variation of the compass I found to be 4° 46' easterly, this being the result of a great number of trials made with four of Dr Knight's needles, adapted to azimuth compasses. These compasses I thought the best that could be procured, yet when applied to the meridian line, I found them to differ not only one from another, sometimes a degree and a half, but the same needle, half a degree from itself in different trials made on the same day; and I do not remember that I have ever found two needles which exactly agreed at the same time and place, though I have often found the same needle agree with itself, in several trials made one after the other. This imperfection of the needle, however, is of no consequence to navigation, as the variation can always be found to a degree of accuracy, more than sufficient for all nautical purposes. SECTION XX. _A Description of several other Islands in the Neighbourhood of Otaheite, with various Incidents; a dramatic Entertainment; and many Particulars relative to the Customs and Manners of the Inhabitants_.[38] [Footnote 38: Several additional particulars respecting the islands here spoken of, are given on the authority of the missionary account, and other works, to which it is unnecessary to refer particularly.--E.]