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 — (this 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 level 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 seal 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 



