4 
THE REV. W. WHEWELL ON THE TIDES OF THE PACIFIC, 
recesses of the coast ; which will be expressed by drawing the cotidal lines of two 
hours, three hours, &c. (II. IIL,&e.) belonging to the tides derived from the oceanic 
tide I. ; and by drawing the cotidal lines of VIII. IX., &c., derived in like manner 
from the oceanic tide VII. (See fig. 2.) 
10. But, moreover, if CD be the shore transverse to the line of no tide AB, 
it is very possible that the tide may not be absolutely simultaneous from C to D, 
but may vary continuously along this shore, although the tide in the central 
oceanic parts be of the nature of a stationary undulation, as already supposed. 
In this case, the state of the tides will require that, in 
a map, we should place the extremity A of the line of no 
tide at some distance from the shore, and there will be a series 
of cotidal lines I. II. III. IV. V. VI. VII., which will revolve 
about the point A, and will carry the tide in succession to all 
the points of the coast CD. These lines will have the general 
form of cotidal lines which we have described ; and will be 
determined in their details by the shore along which the pro- 
gressive tide-wave travels. (See fig. 3.) 
11. But there is yet another modification which the cotidal spaces of the oceanic- 
tides undergo, in passing into the cotidal lines of littoral tides. The oceanic tides 
produced by a stationary undulation, with its midline of no tide, give tides neces- 
sarily differing six lunar hours from each other on the opposite sides of the ocean. 
It is high water on one side when it is low water on the other. Now this cannot be 
the case all over an ocean which is of different breadths in different parts ; nor, in 
fact, can it be the case in any part of it. For that motion of the parts of the fluid 
which a stationary undulation requires, cannot take place on a shore shallow in pro- 
portion to the depth of the oceanic spaces. Near the shore, we shall have a tide 
which is progressive from the oceanic space towards the land. Flence, even when 
the tide occurs at the same time along a great extent of shore on one side of an ocean, 
we cannot assume that it is directly produced by the oceanic tide. It may be a tide 
which is later than the oceanic tide, and which may be represented by a cotidal line 
bordering the space which the oceanic tide occupies. (See fig. 4.) 
12. And this may be the case with regard to a detached 
island, as well as to an extensive coast ; especially if the 
island be the summit of an extensive part where the ocean 
grows shallower. In such a case the island may have 
about it cotidal lines in the form of rings. (See fig. 4.) 
13. From these considerations, it appears that it must be 
very difficult to determine the time of high water in the 
oceanic spaces. All that can be certainly known is, that 
the time must be earlier than the earliest neighbouring 
littoral tides. And such an oceanic tide being assumed, the 
Fig. 4. 
Fig. 3. 
