THE NORTH SEA AND ENGLISH CHANNEL. 
709 
tions arising from extraneous causes, which are now known, and for which an 
allowance can be made, the streams of the Channel turn sufficiently near to the' 
times of high water on the shore of Dover to be considered as simultaneous, without 
occasioning any error that can be of the smallest consequence to shipping*. 
I shall now pass to the next point of interest, — the supposed rotatory motion of the On the rota- 
stream in the English Channel and the North Sea. It will be seen by the Charts, oftLTtreTm 
that wherever any circular motion of the water appears, it occurs between the outer 
extremities of the Channel tide and the stream of the oceanic or parent wave ; and 
is clearly to be accounted for by the streams acting obliquely upon each other. 
Captain Martin White and Mr. Gr^me Spence, who have written upon the tides Erroneous 
of the English Channel, were of opinion that this rotatory motion was not only ap- ^e- 
o } r ^ j f specting this 
plicable to the whole of the Channel, but common to the tides of all the world. Cap- motion. 
tain White, in his remarks upon currents, &c., observes, at p. 35, “ Tides are governed 
by a regular periodical reciprocation in most parts of the world, making the round 
of the compass almost everywhere during the twelve hours. This rotatory motion,” 
he continues, “is perfectly symmetrical during and after a series of moderate weather, 
and the curves it assumes resemble the form of spiral curves." It was Mr. Gr^me 
Spence, however, who originated this idea of a revolving tide-f-. It is a singular 
circumstance that the observations of these officers should not have extended to 
parts of the Channel where the stream runs true, but have been confined to the mixed 
tide. Mr. Gr^me Spence obtained his observations in the vicinity of the Scilly 
Islands, where the streams of the Atlantic and of the English Channel unite ; Captain 
White’s observations extended further up the Channel, but still not far enough to be 
clear of the effect of the Gulf of St. Malo. M. Monnier:|;, who has often been Cause of this 
quoted as the well-known author of a pamphlet on the tides of the English Channel, 
^ ^ ^ o ^ opinion ac- 
derived opinions similar to those above-mentioned, from observations made about counted for. 
the Channel Islands also ; and was confirmed in his opinions by some observations 
made about the same time by Captain FIewitt in the North Sea, near the Lemon 
and Ower sands, which, curiously enough, are on the border of the mixed tide of the 
* In my paper upon the tidal phenomena of the Irish Sea, I particularly referred to the nearly simultaneous 
turn of the stream in that channel which is also under the influence of a combined wave. Since that time ob- 
servations have been made at the Smalls Lighthouse, at the Kunibeg and at other light-ships ; all of which 
have confirmed in a very satisfactory manner those remarks. 
At the Smalls, for instance, situated at the entrance of the Irish Channel, and differing from Liverpool nearly 
five hours in its establishment, the time of slack water occurs fourteen minutes only before high water at Liver- 
pool ; at the Kunibeg, twenty-one minutes before ; then the mean of the intervals in the first page of observa- 
tions, between Smalls and Bardsey, gives four minutes after Liverpool ; the mean of the next page of observa- 
tions thence to Holyhead, thirteen minutes after ; going northward, the mean of the next page, twelve minutes 
after-, off the Isle of Man, at the same time-, and in the North Channel, twenty-four minutes after. 
So that throughout the Irish Sea, as in the Channel which separates England from the Continent, the stream 
slacks throughout at nearly the same time as the combined wave is matured ; or as the time of high water at 
the virtual head of the tide, as already stated in my first report. 
t See his observations on the tides of the Scilly Islands. I Memoire sur les Courants de la Manche. 
4 Y 
MDCCCLI. 
