Proceedings of the British Association. 335 
3. Mr. Whewell gave an account of the proceedings of the com- 
mittee appointed to fix lines of the relative level of sea and land. 
He commenced by saying, that as in the discussion of the relative 
level of land and sea, the tides of the ocean were an important ele- 
ment, he should preface the remarks upon that subject, which he 
intended to submit, by making a few observations upon the very 
valuable communication of his friend Mr. Lubbock. is commu- 
nication he highly eulogized, and pointed out to the Section the im- 
portance of many of the conclusions, should they prove hereafter 
to be generally applicable ; but he expressed strongly his fears that 
this would not be the case. Observation had, in the instance of 
the tides, far outstript theory, for many reasons, which it would be 
impossible to detail; but among the most prominent were the com- 
plexity of the problem itself involving the astronomical theories both 
of the sun and moon; the masses of these bodies; the motions of 
disturbed fluids, and local causes tending to alter or modify the gen- 
eral geographical effect of the great tide-wave at any particular place. 
_ It was upon a careful review of these considerations, that he was led 
to fear that it would be still many years before theory would become 
so guarded and supported by local observations, as to afford a suffi- 
ciently correct guide to be implicitly relied on in these speculations. 
He instanced the tides of the Bristel Channel, which in conse 
of their excessive magnitude, afforded magnified representations of 
the phenomena by which the deviations become more remarkable. 
At the port of Bristol, the tide rose to a height of fifty feet, while 
towards the lower part of the channel it only rose twenty, and along 
other parts of the coast not quite so high. ‘The most striking of 
Mr. Lubbock’s conclusions was that by which it appeared that the 
ocean assumed the form of the spheroid of equilibrium, according to 
the theory of Bernouilli but at five transits of the moon preceding 
the tide itself. By the calculations of Mr. Bent, however, it would 
appear, that although the observed laws of the tides at Bristol might 
be made to agree with Bernouilli’s theory of equilibrium tides, by 
referring them to a certain anterior transit,—so far as the changes 
due to parallax were concerned, as also as far as those due to de- 
clination were concerned,—yet it turned out that this anterior period 
itself was not the same for parallax as for declination. The two 
series of changes have not therefore a common origin or a common 
epoch ; so that in fact there is no anterior period which would give 
retical tides agreeing with observed tides; and, therefore, at 
