6 
THE REV. W. WHEWELL ON THE TIDES OF THE PACIFIC, 
and Ascension ; while at Tristan d’Acunha, a detached island like the others, but re- 
moved out of this medial space, the rise is eight or nine feet. This would explain also 
many of the circumstances which made it so difficult to give any possible form to the 
cotidal lines in the Atlantic ; for instance, the tide occurring nearly at the same time 
all the way from the Cape of Good Hope to the Congo. This is accounted for if we 
suppose that the South Atlantic is mainly occupied by the oceanic tide, and that this 
area is bordered by cotidal lines nearly parallel to the shore. I must confess, how- 
ever, that at present I am unable to carry this hypothesis into comparison with the 
general body of the facts. Such a comparison would require observations much 
more numerous than we as yet possess ; and, as I have already said, even with nume- 
rous observations, we can only hope to draw the cotidal lines in the neighbourhood 
of the shores. 
18. For the same reason I shall not attempt to determine the general course of 
the tides in the Pacific ; but I will remark that the view now given of the distribu- 
tion of the tides in an ocean explains several of the features of the Pacific tides which 
were before very perplexing’. If we suppose an ocean tide from the borders of which 
proceed tides having their progress marked by cotidal lines, we can easily draw the 
lines so as to include the following facts of observation ; — 
(1.) The easterly motion of the tide-wave round Cape Horn, which is established 
by Capt. King’s observations^, and which, as I formerly observed-f', is difficult to 
reconcile with the supposition of a tide revolving from west to east round the south 
pole. This is explained by its being a tide proceeding from the oceanic tide. 
(2.) The tide being at nearly the same hour along a large portion of the coast of 
South America, namely, from the western extremity of the Straits of Magellan for 
twenty or thirty degrees northward. This shows that the cotidal line is nearly 
parallel to the shore. 
(3.) The very small tides or no tides at the islands in the centre of the Pacific, 
Tahiti, and the Sandwich Islands. These belong to a central portion of the ocean, 
where the rise and fall of the surfaces nearly vanishes. 
19. I shall now proceed to give such materials for a knowledge of the tides of the 
Pacific as I have been able to collect, in addition to those which I had under my 
notice in my former Essay. They are for the most part derived from tide observa- 
tions made under the direction of naval officers employed on expeditions of survey 
and discovery. The series of observations at each place was often necessarily brief 
and inexact ; and therefore it is no reflection upon the skill and care of the officers 
and men to whom we owe them, to say that they are often wanting in correctness. 
20. There are, moreover, two other sources of inaccuracy in tide observations ; 
namely, the want of a clear understanding as to the thing to be observed, and the 
irregularity or complexity of the facts themselves. With regard to the former point, 
I hope that several misapprehensions formerly prevalent among navigators are now 
* Sailing Directions. t Philosophical Transactions, 1833, p. 19’2. 
