the earth similar to the magnetic equator, or circle of no dip, like it dividing its circumference into two nearly equal portions, and with which it was until lately erroneously considered to be identical. Upon this circle there is a spot where the intensity is at a minimum, now to be the particular object of our investigation, together with the direction of that circle, and the form and extent of the lines and ovals of isodynamic or equal intensity.
In order to accomplish these several objects, it became necessary to pursue a course widely different from that usually followed by vessels bound to St. Helena, and imposed upon us the tedious operation of beating up to that island against the trade wind, an experiment seldom, if ever, attempted, and in our dull-sailing ships could only be effected by the sacrifice of a considerable portion of time. As we stood Dec. 16.to the southward we crossed the circle, or equator of less intensity, in lat. 19° S. and long. 29° 15′ W., two hundred miles more to the northward than previous observations had led us to expect.
Dec. 17.On the morning of the 17th December, the island of Trinidad was seen; and at 7h. 30m. a.m. Commander Crozier and I, accompanied by several officers, left the ships. After pulling along the leeside of the island, we at length landed in a small cove, a short distance to the northward of the Nine Pin Rock, of Halley, the surf on all other parts being too great to admit of it without hazarding the destruction of our boats. The island is a mass of volcanic matter, and rises abruptly on