SOUTHERN MAGNETIC EXPEDITION.—Extract of a Letter from an Officer of Erebus, 7th February, 1840.—”On the 20th November we left Porto Praya, and December 2nd and 3rd examined and took observations on a cluster of rocks called St. Paul,—evidently the summit of a submarine peak. The sea would make a clear breach over them in blowing weather, consequently nothing vegetable is found. The geological specimens will prove interesting; their general character platonic, with blue lava and conglomerate. Crabs and sea birds were breeding, and the rocks are quite white with the dung of the latter.

“December 17th we landed on Trinidad, to make magnetic observations, and December 24th we crossed the magnetic equator, in latitude 14° 1’ S, after which in the teeth of a S.E. trade we worked up to St. Helena, having completed a chain of dips from England to that place.

“Perhaps the most interesting of our achievements will be the fact of our having gained bottom, at two thousand four hundred and twenty six fathoms, in latitude 27° 24’ S. longitude 17° 30’ W. both ships being becalmed on the edge of the S.E. trade. A line of 3600 fathoms of spun-yarn being prepared, a weight of 721bs was attached to it, and two boats were lowered to buoy up the line. The first 100 fathoms took 35 seconds reeling off,—the last nearly 6 minutes ; we lifted the lead more than once, but of course the spun-yarn broke in the attempt to haul it up.”