Page:A Voyage to Terra Australis Volume 2.djvu/66

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The stone of the hill had in it specks of quartz or feldtspath, and was not much unlike that of Pier Head; but it had a more basaltic appearance. A piece of it applied to the theodolite, drew the needle two degrees out of its direction, and yet the bearings did not show any great difference from the true variation; for an amplitude taken on board the ship by Mr. Flinders, when the head was N.N.E., gave 6° 18′, or corrected to the meridian, 7° 17′ east, and the variation on the eastern side of the hill was 8° 15′, according to the back bearing of Pier Head.

From an observation of the sun's upper and lower limbs in an artificial horizon, the latitude was 21° 50′ 18″, and the ship bore from thence S. 68° E. two miles and a half; the latitude of the ship should therefore have been 21° 51′ 14″; but a meridian altitude observed to the north by lieutenant Flinders, gave 21° 49′ 54″; and I believe that altitudes from the sea horizon can never be depended on nearer than to one minute, on account of the variability of the horizontal refraction. From this cause it was that, when possible, we commonly observed the latitude on board the ship both to the north and south, taking the sun's altitude one way and his supplement the other, and the mean of the two results was considered to be true; separately, they often differed 1′, 2′, and even 3′, and sometimes they agreed. The observation to the north most commonly gave the least south latitude, but not always, nor was there any regular coincidence between the results and the heights of the barometer or thermometer; though in general, the more hazy the weather, the greater were the differences. At this time, the wind was light from the eastward and weather hazy; the thermometer stood at 72°, and barometer at 30,15 inches.

At two o'clock we got under way to go up Broad Sound, it being then near low water. After steering south-east one mile, the depth rapidly diminished and we tacked; but the ship was set upon a bank of sand, where she hung five minutes and then swung off. I afterwards steered nearer to the shore, in deeper water; and at