Narrative of the surveying voyages of his majesty's ships Adventure and Beagle (vol.2- Appendix): between the years 1826 and 1836 : describing their examination of the southern shores of South America, and the Beagles's circumnavigation of the globe

296 APPENDIX. ments of water never reached, lliat they were caused by %nnd I proved by the logs of ships, which were in the respective gales at the time their eiFects on the sea were thus felt at a great distance. ITie places to wliich I particularly allude are the Cape "\"erde Islands, Ascension, St. Helena, Tristan d'Acunha, Cape Frio, Tierra del Fuego, Chiloe, the coast of Chile, the Galapagos Islands, Otaheite, the Keehng Islands, Mauritius, and the Cape of Good Hope. Waves, or rollers, caused by earthquakes, or volcanic eruptions, are, of course, unconnected with wind or atmospheric pressure. But in accounting for currents, as occasioned in some if not many instances by tidal pressure, or a succession of tidal impulses, we must not overlook the well known power of wind in giving horizon- tal motion to water, as well as in elevating or depressing it. Wind blowing almost always in one direction is knowTi to com- municate a movement to waters, and it is remarkable that the gene- ral movements of the North Pacific as well as the North Atlantic are from west by the north to east, or, as a sailor would say, ' with the sun ;' while in the southern oceans. Pacific, Atlantic, and Indian, they are generally ' against the sun,' or from west to east by the south — both corresponding to the general turn of the winds in the respective hemispheres. The Chile current after coasting Peru, presen'es a temperatiu-e of about 60° up to the Galapagos, and there it meets a warm stream out of the Gulf of Panama, at a tempera- ture of about 80°. The two unite together and turn westward along the equatorial zone. There is a remarkable exception on the east coast of Patagonia, where the current sets northward, owing, probably to tides. I cannot end this imperfect attempt to sketch out some of the movements of ocean, without reminding young readers to whom the subject may not be so familiar as it is to others, that there may be circidations of water in a vertical direction, or in a plane inclined to the horizon, as weU as horizontally : and that bodies of water differing in temperature, as well as in chemical composition, do not hastily blend together. Their reluctance to mix is observable at sea, when we sail out of one current, or body of water, into another differing perhaps in temperature, chemical composition, and colour. At the meeting, or edge, of such bodies there is usucJly a well defined line, often considerable ripplings, which indicate some degree of mutual horizontal pressure — as of separate masses.