MADE ON THE COASTS OF EUROPE AND AMERICA IN JUNE 1835. 297 
respecting these tides*. Knowing the anomalies which prevail in this neighbourhood, 
I do not now doubt that Captain Mudge’s statements are all entirely correct. 
Anomalies, but much smaller in amount, may be noticed at Cahore Point in Wex- 
ford, at the bays in the neighbourhood of St. Alban’s Head, and at Freshwater in the 
Isle of Wight. I may observe that the occurrence of such irregularities, at the ex- 
tremity of the space within which one tide is modified by another, is easily explicable. 
A difference of height or of wind, from one half-day to another, may cause one tide 
to affect the other much more or less ; and thus the mixture of tides, which so en- 
tirely alters the tide-hour, may, at these limits, take place very inconstantly, and to 
a very variable amount. 
Sect. 3. On a Second Approximation to a Map of Cotidal Lines , and especially of those 
of the German Ocean. 
17- By means of the observations and reductions above described, I have con- 
structed a map of the cotidal lines which pass near the shores of Europe, and a map 
for the German Ocean and the British Isles in particular, which are given with this 
paper. By reference to these maps, and by comparison of them with the Tables of 
Establishments which I have also given, the reader will see the general results of the 
observations, and their evidence. 
He will also see in one of the maps the difference between this second approxima- 
tion and the first approximation, which I formerly published. The cotidal hours 
which I have used in this case, however, correspond to the correct establishment, and 
not to the vulgar establishment, or time of high water at syzygy, which I used in 
my former essay. But it is easy to make allowance for this difference ; for the correct 
establishment, at London and Liverpool, is very nearly half an hour smaller than the 
vulgar establishment, and for our purpose may for the present be considered as ex- 
actly^so at all places. And hence the l^ h cotidal line of my present map represents 
the 2 h line of the former one, and so on for the rest. 
The correct establishment, which is the meaff of the lunitidal intervals, may also 
be considered as the interval at which the high water follows the moon’s transit at 
the highest spring tides and lowest neaps, for these correspond to the mean lunitidal 
interval. 
I have not presented with this paper a map of the cotidal lines of the coast of 
North America, formed on the new materials ; but I may observe that my former 
map is here considerably in error. The XI. hours cotidal line should strike Cape 
Hatteras ; and the tides diverge from this both to the north and south, as has already 
been stated in art. 12. 
The general views concerning the form of the cotidal lines already stated in Sect. 2, 
might be used in improving the form of the lines belonging to other places, as well 
as those to which the recent observations belong. But as a few years will, it may be 
* Philosophical Transactions, 1833, p. 182. 
MDCCCXXXVI. 2 Q 
