THE VARIATIONS OF PARALLAX OR RECLINATION. 483 
ftion tobe the altitude of Dunbury Hill 
referred to the level of the sea: if that 
level of the sea were taken at Bristol, 
where the tide rises, as before stated, 
fifty feet, the level of low water would 
differ from the same level on the sea 
coast at Devonshire, where the sea rises 
say eighteen feet ; and supposing, as 
is most probable, the place of mean tide 
to be the true permanent level by no 
less a quantity than sixteen feet, which 
would therefore make that hill to ap- 
pear sixteen feet higher, upon a hydro- 
graphical map constructed by a person 
taking his level from the coast of De- 
vonshire, than it would appear upon 
the map of an engineer taking his level 
at Bristol. In the method proposed, 
the lines of equal level would run, sup- 
pose from Bristol to Ilfrocom in one di- 
rection, and from Bristol to Lyme Re- 
gis in the other, and by these a 
common standard of level would soon 
be obtained for the entire coast. 
Professor Sir William Hamilton rose 
to express the sincere pleasure he felt at 
the masterly expositions of Mr. Lub- 
bock and professor Whewell. One 
conclusion to which Mr. Lubbock had 
arrived was to him peculiarly interest- 
ing, viz. that by which it appeared that 
the influence of the Moon upon the 
tides was not manifested in its effects 
until some time after it had been exert- 
ed, for a similar observation had re- 
cently been made by Professor Han- 
xeen respecting the mutual disturb- 
ances of the planets — Mr. Lubbock 
rose to say, that the agreement between 
the results calculated from the theory 
of Bernouilli and those obtained from 
actual observation, were much more 
exact than Professor Whewell seemed 
to imagine ; in truth, so close was the 
agreement, that they might be said ab- 
solutely to agree, since the difference 
was less than the errors that might be 
expected to occur in making and record- 
ing the observations themselves. — Mr. 
Whewell explained that he wished to 
confine his observations to the Bristol 
tides, as these were the observations to 
which he had particularly turned his 
attention ; and, with respect to which, 
he should be able, at the present meet- 
ing, to exhibit diagrams to the Section, 
which he felt confident would amply 
bear out his assertions respecting these 
tides. — Mr. Lubbock stated, that so 
near, indeed so exact, had been the 
coincidence between the observation* 
made at London and Liverpool, and the 
theory, that he was strongly inclined to 
believe that, that coinciden-ce would be 
found at length to be universal. — Pro- 
fessor Stevelly inquired, from Mr. Lub- 
bock, whether he did not think it quite 
possible that local causes might exist, 
which \yould be fully capable of pro- 
ducing the deviations from the theory 
of Bernouilli ; as, for instance, in the 
case of Bristol, so ably insisted upon by 
Professor Whewell, where the causes 
of the extraordinary elevation are the 
landlocking of the tide-wave as it as- 
cends the narrowing channel, and the 
reflexions of other tide-waves from se- 
veral places. Now, particularly in the 
case of reflex tides, may it not so hap- 
pen, and does it not, in fact, happen in 
several places, that they bring the 
actual tide to a given port at a 
time very different from that at 
which the influence of the Moon and 
Sun, if unimpeded, would cause it to 
arrive, and thus separate, as Professor 
Whewell had stated, the origin or epoch 
of the variations due, suppose to paral- 
lax and declension, and even cause 
other divisions from Bernouilii’s theo- 
ry ? — Mr. Lubbock replied, that un- 
questionably it might so happen; but, 
in his opinion, the discussion of a few 
observations, like those made at Bristol, 
could not be expected to point out very 
exactly the origin or epoch of either of 
the variations of parallax or declination, 
with sufficient exactness, to furnish se- 
cure data for determining that they di'd 
not correspond to any one common 
previous transit of the Moon. 
Professor Whewell, who had left the 
room for a few moments, now returned 
with some diagrams, which tended to il- 
lustrate his view of the question ; and, in 
particular, he drew the attention of the 
Section to the circumstance, that the di- 
urnal inequality, which was now begin- 
ning to be observed, decided the ques- 
tion, inasmuch as its epoch could not 
by any means be attributed to the same 
previous transit of the Moon to which 
the others were referred. — Mr. Frend 
congratulated the meeting upon the 
prospect now held out of determining 
precisely that most important practical 
question, the true level of the sea. 
The President then called on Mr. 
£ubbock for his communication res- 
