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

292 Al'PKNDIX. vative wave occupies in moving from Cape Virgins to the Colorado, it alternately augments or diminishes two floods and two ebbs of the great ocean. Perhaps, indeed, it reaches farther and affects the water about the Plata. The extraordinary ' races' about the Peninsula of San Jose, and the apparent absence of currents about the straight coast extending eastward from Blanco Bay, may be attributed to conflicting tidal im- pulses. Why there should be no tide in the River Plata, situated and shaped as it is, seems extraordinary ; but as it is high water at 6h. on the coast of Brazil, and at Sh. about Blanco Bay; and as a derivative wave from this neighbourhood must move eastward and northward, there is a filling up, from the southward, as an ebbing takes place in consequence of a regular six-hour tide ; and vice versa. Tristan d'Acunha has a considerable rise of tide, about eight feet, though Ascension and St. Helena have only about two feet. The former place is aff'ected by a great southern tide ; the two latter are influenced by the comparatively small tide which traverses the space between Africa and Brazil. In the West Indies there are varieties of tides, caused by primary and derivative impulses, exceedingly modified by local circumstances : none however are large, while some are as small as those of Ota- lieite — scarcely a foot at the utmost. There are places also in that archipelago where there is only one tide in twenty-four hours. In considering the West-India tides, those of the east coast of North America, and the exceedingly high ones of Fundy Bay, the gulf stream ought not to be overlooked, as it may aff'ect the tides on the coasts it traverses even more than those on the Patagonian coast are altered by the current driven along it from near Tierra del Fuego. I may here remark that Mr. WheweU was misled by inaccurate data respecting several times of high water, of material consequence to his cotidal lines. At the Western Islands he had 1|^ and 2j, where there ought to have been 4}, according to Mendoza Rios' tables, confirmed by the Beagle's observations ; at Madeira he used l^, the time of the stream changing, instead of 4, the time of high water ; at the Cape Verde Islands he took the time of low tide, instead of that of high water ; his 5h. line is near Ascension, whei'e the time of high water is 6.20 ; and his 2h. line is close to St. Helena, where the time is about five. The deficiency of data is so great, owing to mistaking