Page:A Voyage to Terra Australis Volume 2.djvu/537

On ship-board.] greatest west variations had happened, the ship's head was North and Easterly; and that when those, where it was least, had been observed, it was South and Westerly." (The greatest west variations in the southern hemisphere were observed with the head East, on board the Investigator, and the least with the head West.) "I mentioned this to captain Cook, and some of the officers, who did not at first seem to think much of it; but as opportunities happened, some observations were made under those circumstances, and very much contributed to confirm my suspicions; and throughout the whole voyage I had great reasons to believe, that variations observed with a ship's head in different positions, and even in different parts of her, will differ very materially from one another; and much more will variations observed on board different ships, which I now find fully verified, on comparing those made on board the Adventure with my own, made about the same time" in the Resolution.

Mr. Wales did not quit the subject here. In the introduction to captain Cook's third voyage, published in 1785, is a paper from the same careful observer, citing a variety of cases wherein differences were found in the variation of the compass. These cases are as follow.

1st. Putting the ship's head a contrary way: differences 3° to 6°, and even 10°.

2nd. At different times of the same day: differences 3° to 7°.

3d. Being under sail, and at anchor in a road-stead: difference 5°.

4th. On board different ships: differences 3° to 5°.

5th. Near the same place; at different times in the voyage: 4° and 5°, or upwards.

6th. In different compasses: 3° to 6°.

That the variation should be different on changing the direction of the ship's head or the place of the compass, and also on board different ships, is perfectly reconcileable to the explanation I have given; but that it should vary so much at different times of the same day or year,—when under sail and at anchor,—or even in different compasses, much surprised me, if all other circumstances were the same. I was therefore induced to examine the instances quoted under each case; and found great reason to believe, not only that the direction of the head was changed in most, if