6 EIGHTH lllCI'ORT — 1838. 



BridgewHter) in which is inserted horizontally, without lead, a 

 copper cylinder an inch and a half diameter and fourteen inches 

 long. In order to prevent this bolt being drawn, it is fastened 

 with a copper key passing through a transverse hole into a 

 notch in the bolt, and the transverse hole is filled with lead. A 

 similar block of granite, (also presented by the corpoi'ation of 

 Bridgewater) with a similar copper bolt, is the mark at Wick' 

 rocks, in the parish of Stogursey near Bridgewater, which stands 

 on the property of Sir Peregrine P. Acland, Bart. The mark 

 at Axmouth is a similar block of granite, procured by J. H. 

 Hallett, Esq., of that place, on wliose property the mark 

 stands, and who has manifested a great disposition to forward 

 the operations in every way. The kindness and liberality of the 

 gentlemen who have been mentioned, on whose ground the marks 

 have been inserted, have much forwarded the undertaking, and 

 deserve the best acknowledgement the British Association can 

 make. These gentlemen are also willing to perpetuate the obli- 

 gation which science thus owes them, by allowing themselves to 

 be considered the guardians of the permanent level marks thus 

 existing on their property ; and this is a kindness the more 

 valuable, since the British Association neither has nor can have 

 any valid right to such services. The marks of which this 

 statement contains the record, may hereafter be of great conse- 

 quence in settling important questions of a scientific nature, if 

 their pi*eservation be, as we do not doubt it will be, kept in mind 

 by the proprietors of the estates above mentioned. 



There is also a bolt inserted in the Avail of the church at Ax- 

 mouth ; and it is intended to place a similar mark in the church at 

 Uphill, a village situated where the level line crosses the western 

 extremity of the Mendips. 



With the permanent level points at Axmouth, Wick rocks, 

 and Portishead, the surface of the sea was compared by means of 

 tide observations made at first for a month at each of those places. 

 In pursuance of the views already stated, the mean of high and 

 low water was taken as representing the level of the sea. In 

 fact, this level of " mean water" is so nearly constant, that even 

 a few days will give its position with tolerable accuracy ; and 

 observations continued for a fortnight, which of course includes 

 spring tides and neap tides, give the result with great precision. 

 The first result was, that while the level of mean water at Ax- 

 mouth and at Wick rocks did not differ by more than a small 

 fraction of an inch, the level of mean water at Portishead was 

 four inches and a half lower than at the other places. As how- 

 ever it appeared possible that this difference might result from 

 the observations being made at different times of the year, further 



