To give myself the best possible chance I flung off my jacket and kicked off my shoes, retaining only my shirt and trousers.  Then, casting off the lashings by which I had secured myself to the shattered mainmast, I stood up, and carefully took the bearings of the _flotsam_ relative to the sun, to guide me when swimming.  This done, I poised myself upon the spar preparatory to diving off the mast, and had raised my hands above my head, when not half-a-dozen fathoms away, and immediately between me and the spot for which I was bound, I saw the dorsal fins of two enormous sharks sculling quietly to and fro, as though to blockade me and cut me off from my only hope of escape.