140 Royal Society. 



America in June 1835 '). Among the results obtained in the latter 

 paper, it appeared that all the " cotidal lines " which have been most 

 exactly traced, meet the coast at a very acute angle ; and for that 

 and for other reasons stated in other memoirs, the drawing of cotidal 

 lines across wide oceans is a very precarious process. In addition 

 to this consideration, the scantiness of our materials has hitherto 

 made it impossible to trace the tides of the Pacific in a connected 

 form; and the absence of lunar tides in the central parts of that 

 ocean (as at Tahiti) makes it difficult to represent the course of the 

 tides by means of cotidal lines at all. We are thus led to consider 

 in what other way the course of the tides over wide spaces may be 

 represented : and it is stated by the author, that either a stationary 

 undulation, or a rotatory undulation, of the central parts of an ocean, 

 with a border of cotidal lines proceeding outwards from the central 

 undulation into bays and arms of the sea, would represent, in a great 

 measure, the tidal phenomena of the Atlantic and Pacific, as far as 

 they are known. The rotatory undulation here spoken of need not 

 be understood to be a rotatory motion of the water, but a geometrical 

 rotation of the cotidal line, such as takes place in the German Ocean ; 

 the tide in the central part (that is, the rise and fall of the surface) 

 vanishing, as was shown by the observations of Capt. Hewett, though 

 the tidal currents at that point alternate regularly. Such a move- 

 ment of the cotidal line may perhaps represent the phenomena of the 

 North Pacific. 



The author has collected materials for a Tide Map of the Pacific 

 from various navigators ; — Cook, Flinders, King, Captains FitzRoy, 

 Sir E. Belcher, Sir James Ross, Stokes, Killet, and others of our 

 own countrymen; Malaspina, Freycinet, Du Petit-Thouars, Wrangel 

 and Admiral Liitke, and other Spanish, French and Russian navi- 

 gators. The result of these appears to be, that on the eastern coast 

 of the Pacific, the tide comes from the west ; arrives first at the coast 

 near Acapulco and Nicoya, and is later and later both to the north 

 and to the south of this point ; passing to the eastward round Cape 

 Horn, as observed by King, and to the northward along the coast 

 of North America, and then to the westward along the Aleutian 

 Isles, and so to Kamtschatka, as stated by Admiral Liitke. 



The tides in the centre of the Pacific are too small and anomalous 

 to allow us to trace the connection among them. At Tahiti, accord- 

 ing to the observations of Sir Edward Belcher, the solar and lunar 

 tides appear to be equal. 



The tides have been traced along the coasts of New Zealand and 

 Australia by Cook, Flinders, and other succeeding navigators. They 

 come from the east ; and the cotidal lines which mark their pro- 

 gress appear to have a north and south range, except when deflected 

 by passing round promontories and the like. When we pass] west- 

 ward from the eastern coast of Australia, the cotidal lines are too 

 much broken and complicated by the intervention of islands, to be 

 traced with our present materials of knowledge. 



The second part of the memoir, " On the Diurnal Inequality," treats 

 of the diiference of the two tides of the same day, which has also 



