10 
THE REV. W. WHEWELL ON THE TIDES OF THE PACIFIC, 
probably be the case in other instances where the cotidal lines affect the same con- 
verging form, and where the tide in the central part of the sea vanishes. 
Materials for a Tide Map of the Pacific. 
24. The materials which I formerly employed in my “Essay towards a First Ap- 
proximation to a Map of Cotidal Lines,” were principally the following: — the collec- 
tion of the facts then known, given in the fourth volume of Lalande’s Astronomy ; 
Books of Astronomy and Navigation, and Sailing Directions, as Norie’s Epitome of 
Navigation, Purdy’s Memoir on the Atlantic Ocean, his Memoir on the Ethiopic or 
South Atlantic, and his Columbian Navigator: Nautical Surveys, as the Surveys 
of the Australian coasts by Captains Flinders and King, and of Patagonia by the 
latter officer; and the Survey of the Pacific by Captain Beechey ; also foreign 
materials of the same kind, as Malaspina’s Voyage, and Roussin’s Survey of Brazil : 
to which may be added the “ Remark Books” of various ships, which I was allowed 
to consult at the Admiralty, Memoirs relative to particular places, and other miscel- 
laneous sources of information. 
25. I have more recently collected other materials of the same kind, which I will 
briefly describe. They are partly gathered from books: for instance, — 
Voyage autour du Monde sur I’Uranie et la Physicienne, pendant les annees 1817, 
1818, 1819, 1820, par M. L. de Freycinet. Paris, 1826. 
One volume of this work, consisting of 356 pages, is entirely filled with tide dis- 
cussions ; and it is mortifying to see so much zeal and mathematics thrown away 
from the want, so general even yet, of a knowledge of the best modes of dealing with 
tide observations. The observations were only made at four places : at Rio Janeiro, 
sixteen days; at the Isle de France, twenty-seven days; at Rawak, fifteen days; at 
Guam, nine days. With the whole of the discussion employed, little or nothing of 
value is obtained ; for even the resulting “establishments” are too vague to be de- 
pended on. 
In the Voyage of the Astrolabe under the command of M. J. D. D’Urville, 1826 
to 1 829, I do not find any tide observations recorded. 
26. Voyage autour du Monde sur la Fregate la Venus, 1836 a 1839, par Abel du 
Petit-Thouars. 
This navigator gives the “establishment” and rise of tide at fifteen places, princi- 
pally on the western coast of America and in other parts of the Pacific. These re- 
sults will be used in the present memoir, along with others ; but I will insert here 
the general remarks which M. du Petit-Thouars makes upon the subject, after 
giving his results. 
“When we see from this table that the tide rises only one-fourth as high at Aca- 
pulco as at la Magdalena ; when we remark differences of two hours and a quarter, 
and of four hours and a half between the tide-hours of ports at small distances from 
each other, and situate on a coast on which the ocean has free range ; when 
