Winds at Tahiti

Altho' this Island lies within the Tropick of Capricorn, yet the Heat is not Troublesome, nor do the winds blow constantly from the East, but are subject to variations, frequently blowing a fresh gale from the South-West Quarter for two or three days together, but very seldom from the North-West. Whenever these variable winds happen they are always accompanied with a swell from the South-West or West-South-West, and the same thing happens whenever it is calm and the Atmosphere at the same time loaded with Clouds--sure indication that the winds are Variable or Westerly out at Sea, for clear weather generally attends the settled Trade.

The meeting of Westerly winds within the general Limits of the Easterly Trade is a little extraordinary, and has induced former Navigators, when they met with them, to think that they were caused by the nearness of some large Tracks of Land: but I rather think they were owing to another Cause. It hath been found both by the Dolphin and us that the trade winds in those parts of this Sea doth not extend further to the Southward than 20 degrees, and without which we generally meet with a wind from the westward. Now, is it not reasonable to suppose that when these winds blow strong they must encroach upon and drive back the Easterly winds as to cause the variable winds and South-Westerly swells I have been speaking of? It is well known that the Trade winds blow but faint for some distance within their limits, and are therefore easily stopt by a wind from the Contrary direction. It is likewise known that these limits are subject to vary several degrees, not only at different seasons of the Year, but at one and the same season. Another reason why I think that these South-West winds are not caused by the nearness of any large Track of land, is in their being always accompanied with a large swell from the same Quarter, and we find a much greater surf beating upon the Shores of the South-West sides of the Islands situated just within the Limits of the Trade winds than upon any other part of them.

The tides are perhaps as inconsiderable in these Seas as in any part of the world. A South or South by West moon makes high water in Royal Bay, but the water does not rise upon a perpendicular above 10 or 12 inches, except on some very Extraordinary occasions.

The variation of the Compass I found to be 4 degrees 46 minutes Easterly, this being the mean result of a great number of Trials made by 4 of Dr. Knight's needles belonging to the Azimuth Compasses, all of which I judged to be good ones, and yet when applied to the Meridian line I found them not only differ one from another sometimes a degree and a half; but the same needle would differ from itself more or less, the difference sometimes amounting to half a degree, both at the same time and on differant days. This will in a great measure account for the seeming errors that may, upon a nice examination, appear to have been made in observing the Variation inserted in the Course of this Journal. This variableness in Magnetick Needles I have many times and in many places experienced both ashore and on board of Ships, and I do not remember of ever finding two Needles that would agree exactly together at one and the same time and place, but I have often found the same Needle agree with itself for several Trials made immediately one after another.* However, all this is of no sort of consequence to Navigation, as the Variation of the Compass can always be found to a degree of accuracy more than sufficient for all nautical Purposes.

I have before hinted that these People have an Extensive knowledge of the Islands situated in these Seas. Tupia, as well as several others, hath given us an account of upwards of 70; but, as the account they have given of their situation is so Vague and uncertain, I shall refer giving a list of them until I have learnt from Tupia the Situation of each island with a little more certainty. Four of these islands--viz., Huaheine, Ulietea, Otaha, and Bolabola** --we were informed, lay only one or two days' sail to the Westward of George's Island, and that we might there procure Hogs, Fowls, and other refreshments, Articles that we have been very sparingly supply'd with at this last Island, as the Ship's Company (what from the Constant hard duty they have had at this place, and the two free use of Woman) were in a worse state of health than they were on our first arrival, for by this Time full half of them had got the Venerial disease, in which Situation I thought they would be ill able to stand the Cold weather we might expect to meet with to the Southward at this Season of the Year, and therefore resolved to give them a little time to recover while we ran down to and explored the Islands before-mentioned.

Tupia informs us that in the Months of November, December, and January they have constant Westerly winds, with rain; also that the whole island can muster 6780 Fighting Men, by which some judgment can be formed of the number of inhabitants. Each district furnishes a certain number, which the chief is obliged to bring into the field when summoned by the Eare dehi, or King of the Island, either to make war or repell an invasion.***

* These discrepancies result from imperfections in the suspension and mounting of the needles, and are only absent in instruments too delicate for ordinary sea service.

** These islands are now known as Huaheine, Raiatea, Tahaa, and Borabora or Bolabola, and are under French sovereignty.

*** This paragraph is added in Admiralty copy.