1802.
February.
Thursday 18.
for sail needles, marline spikes, or other implements of iron which might have been left in or about the binnacle, but I could fix on nothing unless it were the guns; for it is to be observed, that notwithstanding the constancy of the differences, the idea of any regularly acting cause to derange the needle had not yet fixed itself in my mind. The perfection to which naval science had arrived did not allow me to suppose, that if a constant and unavoidable attraction existed in ships, it would not have been found out, and its laws ascertained; yet no longer than three days before, differences had been observed, sufficient one would think to have convinced any man that they were produced by some regular cause. Off Point Drummond, about fifteen leagues to the north of where the variation 1° 39′ east was observed with the ship's head at south, both azimuths and an amplitude had been taken with the same compass. The first gave 1° 33′ west, the head being south-east-by-east; and after we had tacked, and the head was south-west-by-west, the amplitude gave 3° 56′ east! I did not yet see, that as the ship's head was as much on the east side of the magnetic meridian in one case, as it was to the west in the other, so was the variation as much too far west then, as it was too far east afterward. Differences like this, of 5½°, which had frequently occurred, seemed to make accuracy in my survey unattainable, from not knowing what variation to allow on the several bearings. The guns were removed in the hope to do away the differences, but they still continued to exist, nearly in the same proportion as before; and, almost in despair, I at length set about a close examination of all the circumstances connected with them, in order to ascertain the cause, and if possible to apply a remedy; but it was long, and not without an accumulation of facts, before I could arrive at the conclusions deduced and explained in the Appendix No. II. to the second volume.
We tacked towards the land soon after noon; and being within five miles of it at three o'clock, stood off again. The furthest extreme of the main land was a sloping low point, distant about three leagues; but two or three miles beyond it, to the south,