336 Proceedings of the British Association. 
least the Bristol tides do not at present appear to confirm the result 
obtained by Mr. Lubbock from the London tides. Mr. Whewell 
then illustrated these views by diagrams, by the aid of which he ex- 
plained to the section the luni-tidal intervals, and the curve of semi- 
menstrual inequality—(tbis latter term, and the doctrine connected 
with it, was introduced into the subject of the tides by the professor 
himself.) Prof. Whewell then proceeded to the question more im- 
mediately before him—the proceedings of the committee appoint- 
ed to fix the relative Jevel of the land and sea, with a view to ascer- 
tain its permanence, or the contrary. He observed, that the com- 
mittee had not taken any active practical steps for the important 
purposes for which they were appointed, because they had met with 
many unexpected difficulties requiring much consideration. It was, 
however intended to appoint a committee for the same purposes, 
who should be furnished with instructions founded upon the views 
at which the former committee had by their labors and experience 
arrived. One method proposed was, that marks should be made 
along various parts of the coast, which marks should be referred to 
the level of the sea; but here the inquiry met us in the very outset 
—what is the proper and precise notion to be attached to the phrase 
the level of the sea? Was it high water mark or low water mark? 
Was it at the level of the mean tide, which recent researches seemed 
to establish? In hydrographical subjects the level of the sea was 
taken from low water, and this, although in many respects incon- 
venient, could not yet be dispensed with, for many reasons, one of 
which he might glance at—that by its adoption, shoals, which were 
dry at low water, were capable of being represented upon the maps 
as well as the land. The second method proposed appeared to be 
one from which the most important and conclusive results were to be 
expected. It consisted in accurately leveling, by land survey, lines 
in various directions, and by permanently fixing, in various places, 
numerous marks of similar levels at the time; by the aid of these 
marks at future periods, it could be ascertained whether or not the 
levels, in particular places, had or had not changed, and. thus the 
question would be settled whether or not the land in particular lo- 
calities was rising or falling. Still further, by running on those lines, 
which would have some resemblance to the isothermal lines of Hum- 
boldt, as far as the sea coast, and marking their extremities along 
the coast, a solution would at length be obtained to that most im- 
portant practical question,—what is the proper or permanent level 
