Tanna lies six leagues from the south side of Erromango, extending S.E. by S. and N.W. by N., about eight leagues long in that direction, and every where about three or four leagues broad.
The isle of Immer lies in the direction of N. by E. 1/2 E., four leagues from Port Resolution in Tanna; and the island of Erronan or Footoona East, in the same direction, distant eleven leagues. This, which is the most eastern island of all the Hebrides, did not appear to be above five leagues in circuit, but is of a considerable height and flat at top. On the N.E. side is a little peak seemingly disjointed from the isle; but we thought it was connected by low land. Annatom, which is the southernmost island, is situated in the latitude of 20° 3', longitude 170° 4', and S. 30° E., eleven or twelve leagues from Port Resolution. It is of a good height, with an hilly surface; and more I must not say of it.
Here follow the lunar observations by Mr Wales, for ascertaining the longitude of these islands, reduced by the watch to Port Sandwich in Mallicollo, and Port Resolution in Tanna.
Port Sandwich, ( Mean of 10 sets of ob. before 167° 56' 33" 1/4 ) E.
( 2 ditto, at 168 2 37 1/2 ) long
( 20 ditto, after 167 52 57 )
( ————————
( Mean of those means, 167 57 22 3/4
Port Resolution, ( Mean of 20 sets of ob. before 169 37 35 ) E.
( 5 ditto, at 169 48 48 ) long
( 20 ditto, after 169 47 22 1/2 )
( ————————
( Mean of these means, 169 44 33
It is necessary to observe, that each set of observations, consisting of between six and ten observed distances of the sun and moon, or moon and stars, the whole number amounts to several hundreds; and these have been reduced by means of the watch to all the islands; so that the longitude of each is as well ascertained as that of the two ports above-mentioned. As a proof of this I shall only observe, that the longitude of the two ports, as pointed out by the watch and by the observations, did not differ two miles. This also shews what degree of accuracy these observations are capable of, when multiplied to a considerable number, made with different instruments, and with the sun and stars, or both sides of the moon. By this last method, the errors which may be either in the instruments or lunar tables, destroy one another, and likewise those which may arise from the observer himself; for some men may observe closer than others. If we consider the number of observations that may be obtained in the course of a month (if the weather is favourable,) we shall perhaps find this method of finding the longitude of places as accurate as most others; at least it is the most easy, and attended with the least expence to the observer. Every ship that goes to foreign parts is, or maybe, supplied with a sufficient number of quadrants at a small expence; I mean good ones, proper for making these observations. For the difference of the price between a good and a bad one, I apprehend, can never be an object with an officer. The most expensive article, and what is in some measure necessary in order to arrive at the utmost accuracy, is a good watch; but for common use, and where that strict accuracy is not required, this may be dispensed with. I have observed before, in this journal, that this method of finding the longitude is not so difficult but that any man, with proper application, and a little practice, may soon learn to make these observations as well as the astronomers themselves. I have seldom known any material difference between the observations made by Mr Wales, and those made by the officers at the same time*.
[See Vol I. p40. "Which is nearly the same difference as the day before…">[
In observing the variation of the magnetic needle, we found, as usual, our compasses differ among themselves, sometimes near 2°; the same compass too, would sometimes make nearly this difference in the variation on different days, and even between the morning and evening of the same day, when our change of situation has been but very little. By the mean of the observations which I made about Erromango; and the S.E. part of these islands, the variation of the compass was 10° 5' 48" E.; and the mean of those made about Tierra del Espiritu Santo, gave 10° 5' 30" E. This is considerably more than Mr Wales found it to be at Tanna. I cannot say what might occasion this difference in the variation observed at sea and on shore, unless it be influenced by the land; for I must give the preference to that found at sea, as it is agreeable to what we observed before we made the islands, and after we left them.
CHAPTER VIII.
An Account of the Discovery of New Caledonia, and the Incidents that happened while the Ship lay in Balade.