Page:A Voyage to Terra Australis Volume 2.djvu/61

Thirsty Sound.]

whereas my theodolite stood upon legs, more than four feet high. The dipping needle was raised about two feet; and by its greater inclination at the top of the hill, shows the principal attraction to have been not far from thence. The least dip, 50° 28′, taken at the shore on the north side of the head, was doubtless the least affected; but it appears to have been half a degree too much, for at Port Bowen, twenty-two miles further south, it was no more than 50° 20′. An amplitude taken on board the ship in the Sound by lieutenant Flinders, when the head was S.S.W., gave variation 8° 39′, or corrected to the meridian, 7° 40′ east. As Pier Head lay almost exactly in the meridian, from the ship, its magnetism would not alter the direction of the needle; and I therefore consider 7° 40′ to be very nearly the true variation, when unaffected by local causes: in Port Bowen, it varied from 7° 40′ to 8° 30′ east.

Notwithstanding this very sensible effect upon the needle, both horizontally and vertically, I did not find, any more than captain Cook, that a piece of the stone applied to the theodolite drew the needle at all out of its direction; nevertheless I am induced to think, that the attraction was rather dispersed throughout the mass of stone composing Pier Head, than that any mine of iron ore exists in it. The stone is a porphyry of a dark, blueish colour.

On the 6th, at noon, when the observations were finished and I had proposed to quit Thirsty Sound, the wind and tide were both against us. To employ the rest of the day usefully, I went over in the whale boat, accompanied by the landscape painter, to the 6th, 7th, and 8th Northumberland Islands, which, with many low islets and rocks near them, form a cluster three or four leagues to the north-east of the Sound. Orders were left with lieutenant Fowler to get the ship under way as early as possible on the following morning, and come out to meet us.

Nearly mid-way between Pier Head and the cluster, lie some rocks surrounded with breakers; and until they were passed the depth was from 6 to 8 fathoms, and 11 afterwards. We rowed to a