It was now necessary to determine our position as accurately as we possibly could; for, by our usual and daily reckoning, we made ourselves, at eight a.m., not above fifty or sixty miles from the nearest land, which would be the Island of Barra.

I had, on the previous day, taken a lunar under difficult circumstances, owing to the motion of the ship, and this motion was considerably increased now; but the sky was, though with occasional light clouds, sufficiently clear for the purpose, and the moon was within excellent distance. As I had done before, so now, I determined to take the entire set of observations myself, and work up the altitudes in the usual way.

As this is all mere nautical detail, I will only observe, that it is mentioned to show what difficulties there are in the way of a seaman who has to navigate any ship on the ocean, and also to prove how highly essential and useful lunar observations are at sea.

Now we had been in great doubt about our chronometers for some time past, and had given them a different rate three times: the last was off Possession Bay. Still we were, from many causes, uncertain as to their accuracy; and consequently it was advisable, if possible, to test them by other means. The only means by which we could do this were those similar to my present attempt of finding the longitude from an observed distance between the sun and moon.