194 
SECOND REPORT— 1832 . 
take place very irregularly. At St. Helena the rise in springs, 
according to Dr. Maskelyne,is 89 inches, and in neaps 20 inches; 
and I apprehend that less information could be elicited from a 
year’s observations there, than from a month’s observations at 
the London Docks. When a few observations only are made 
with a view of determining the establishment, they should not 
be used to determine that quantity absolutely, but they should 
be compared with observations at some place of which the esta¬ 
blishment is accurately known, or where observations are con¬ 
tinually carried on. It would be very desirable for those •who 
are able, to combine so as to effect the monography or detailed 
description of the tides through some short extent of coast, 
such as that which has been effected by M. Daussy for the 
coast of France. 
M. Daussy has determined with great care, by means of ob¬ 
servations executed by the “ Reconnaissance hydrographique 
des cotes de France,” undertaken by the body of ing^nieurs 
hydrographes under M. Beautems Beaupr£, the establishment 
of all the principal places on the coast of France between 
Ouessant and the coast of Spain. M. Daussy finds that the in¬ 
fluence of the wind upon the height of high water is insensible. 
I have found that the direction of the wind (unless in violent 
gales,) has no effect upon the phenomena of the tides in the 
river Thames ; but this I attributed to its comparatively shel¬ 
tered situation ; and I should have thought that the tides in the 
Bay of Biscay would be much affected by gales sweeping over 
the surface of the Atlantic. M. Daussy has shown beyond 
doubt that such is not the case, and that the irregularities of 
the tides there must be due to more remote causes. He has 
also shown that the atmospheric pressure has considerable in¬ 
fluence upon the height of the tide ; an inch of rise in the mer¬ 
curial column depresses the tide fourteen inches. This fact 
is very remarkable. I have ascertained, however, that in the 
river Thames the influence of the fluctuations of the barometer 
upon the tide is insensible, or very nearly so. Beyond the 
coasts of France, our knowledge of the progress of the tide- 
wave is very imperfect; and it is difficult at present to trace 
satisfactorily the course of high water throughout the globe, 
owing to the paucity of even bad observations. It is generally 
high water at any given instant at a series of points which form 
the crest of the tide-wave, and which I have called, at the sug¬ 
gestion of Mr. Whewell, cotidal lines. If the ocean were not 
intersected by continents, the tide-wave would proceed from 
east to west; and if the luminaries moved in the equator, the 
cotidal lines would be meridians. 
