THE NORTH SEA AND ENGLISH CHANNEL. 
713 
diminished just one half in extent, its rate of travelling is reduced a like quantity, and 
its streams are almost always in opposition to those of the outer or parent wave. 
Plans 3 and 4 exhibit the forms of this wave at full and change, as they appear Formation of 
at the hours respectively marked against them at the side of the Plan. They are ^ combined 
, ° . wave in the 
constructed principally from the establishments and ranges of tide published in the Strait of 
Philosophical Transactions, 1836, Pprt II., by drawing a line through the fairway of 
the Channel, and setting off upon it the times of high water and the ranges of tide 
as they would exist at the stations seleeted for this purpose. 
In these Plans we can distinctly trace the formation of a combined wave at Dover. 
In Plan 4, for instance, at V hours, the crests of two waves are seen to be formed a 
little beyond the Deadman on one side and at the Spurn Point on the other, and the 
foot of the wave or hollow which they create is resting at Dover. Following the 
progress of these two crests down the page, we find them gradually approaehing 
each other and wearing out the depression in advance of them, until between VIII. 
and IX. o’clock the hollow has vanished ; at X. o’clock there is a decided convexity 
of surface, which gradually increases until at XI. o’clock. Plan 3, the crest has 
attained its zenith : the combined wave is perfected, and it is high water at Dover. 
If now we follow the wave down the same page. Plan 3, as the tide falls, we find 
the crest to become more oblate, and finally, to be obliterated without there being 
any material progress of the wave in either direction. In fact, the wave on this 
section appears to descend nearly perpendicularly, and the progress of the derivative 
waves to be so far destroyed that we can scarcely trace any indieation of their ad- 
vance. On the contrary, we see a new wave on each side preparing to roll up the 
Channel to renew the wave thus clearly common to both. So far then we perceive, 
from these data, that the wave in the Strait of Dover is due to the combined action 
of two waves derived from the parent or Atlantic wave, and which advance from 
opposite quarters. These waves, it may be seen, are materially different in their 
dimensions and rate of travelling from those of the oceanic wave from which they 
are derived. The dotted line drawn through the crests of the wave upon the Plan 3, 
will sufficiently discover the material change it undergoes on approaching the channel 
in which the braneh wave exists. 
The same result, nearly, as regards the formation of the combined wave, is arrived 
at if we take a mean between the seetions of the wave as it would appear from the 
ranges and establishments along the coasts of England and of France and Belgium. 
In this mean section, however, we traee the formation of a combined wave at IX. 
o’clock off Selseabill, and can detect a progressive advance of a small wave thence to 
the eastward, making high water along the Duteh coast in the inverse order of the 
high water resulting from the wave upon the opposite side of the channel, and then 
merging into the wave preparing to renew the order of the tides in the North Sea*. 
* This merging of the waves into each other may possibly be the cause of the whole rise of the tide at the 
Texel occurring in the first half of tide, as stated in “ Ariel,” Remarks upon the Tides of the Texel, published 
at Amsterdam. 
