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 



