9 
THE REV. W. WHEWELL ON THE TIDES OF THE PACIFIC, 
tide observations in which this diurnal inequality prominently appears ; but I have 
now the means of showing it to be much more extensively distributed and larger in 
amount than has been supposed. 
These two points, the Cotidal Lines, and the Diurnal Inequality, will be the subject 
of the present memoir. 
Of Cotidal Lines. 
3. Great light was thrown upon the form of the cotidal lines by very extensive series 
of observations made for that purpose in June 1B34 and June 1835, by the Preventive 
Service at all their stations on the coasts of England, Ireland and Scotland, and by 
naval officers at many points of North America, Spain, Portugal, France, Belgium, 
the Netherlands, Denmark and Norway. These observations, made at my suggestion, 
by the kindness of the authorities of that time, were so numerous and exact as to 
determine with considerable accuracy the form of the cotidal lines in the neighbour- 
hood of the oceanic coast of Europe. One main feature, very prominent in all these 
lines, was that they meet the shore at a very acute angle, and follow its flexures at a 
little distance with an almost parallel course ; and that consequently, the tide- wave 
which runs up a channel is, in the middle of the channel, very much in advance of 
its place at the sides of the channel =*=. This form of the cotidal lines is also easily 
shown to be in harmony with the laws of the motion of fluids-f'; and it cannot be 
doubted that those lines must affect such a form to a much greater extent than was 
assigned to them in my First Approximation. 
This character of the cotidal lines must prevail to such an extent that I conceive 
all attempts to draw such lines across a wide ocean by means of observations on its 
shores, must be altogether worthless. This applies beyond doubt to the Pacific Ocean, 
and probably, taking other reasons into account, to the Atlantic also. 
4. This conclusion is further confirmed by our finding that if we do draw “ cotidal 
lines” across wide oceans, as for instance, the Atlantic, they do not agree with tides 
observed at islands in the mid-ocean, without ascribing to the lines such flexures as 
deprive them of all simplicity, and make them require further evidence. 
5. Again, it is found that, for the most part, the tides in the mid-ocean isles are 
very small ; and this circumstance again, makes the assumed oceanic continuity 
of cotidal lines very doubtful. 
6. Further : if the tides in the Atlantic and Pacific be conceived to be brought by 
a progressive wave, which the scheme of cotidal lines assumes, they must be con- 
ceived to be brought from some part of the ocean where such a wave can travel 
round the globe of the earth so as to follow the moon, or at least, to be connected 
with such a part of the ocean : and such a supposition was accordingly involved in 
* See tEe Charts of the British Isles and of the Coasts of Europe in the Sixth Series of Tide Researches, 
Philosophical Transactions, 1836, Part II. 
t See Mr. Airy on Tides and Waves, Art. 359, in the Encyclopaedia Metropolitana. 
