138 Remarks on some Tide Observations, 



feet, and the smallest from 10 to 29 feet; the differences in 

 the levels of low water being 10 feet, and of high water 17 

 feet. 



Had the differences between the levels of low water of spring 

 tides and of neap tides at King- Road and at the Land's-end 

 been about the same, we might be led to conclude that all 

 the difference of rise and fall would have been due to the in- 

 creased elevation of high water, owing to the narrowing of 

 the Bristol Channel in proceeding upwards, as before stated ; 

 but as the differences of levels of low water at King-Road 

 amount to about ten feet and those at Land's-end only to about 

 five feet, it may be possible that the momentum of the ebb- 

 tide may draw the water down at King- Road at low water to 

 below the level of low water at Land's-end. If it be so then 

 there can be no sure means of comparisons of sea levels at 

 either mean tide, high water, or low water ; but I should con- 

 sider that the low water of neap tides is most likely to be the 

 nearest approximation to a true level, and that the mean level 

 of the sea on the south-west coast of Great Britain is about 

 three feet and a half above the average level of the low water 

 of neap tides. 



In order to ascertain the particular operations of the tides, 

 and their effects in certain localities, it would be desirable to 

 have the tide levels simultaneously taken at convenient places 

 on both the north and south coast, extending from King- 

 Road and from Axmouth to the Land's-end, marking the 

 time and level of high and low water, and the elevation of the 

 sea at every quarter or half hour throughout the day. These 

 observations being connected at each place with some parti- 

 cular bench-mark, would furnish data for comparison when- 

 ever lines of levels might be extended to them. Such lines 

 of levels might be surveyed across Cornwall in sundry places, 

 and might ultimately be connected with the line already sur- 

 veyed from Portishead to Axmouth. 



Although I do not mean to impugn the correctness of the 

 results of the leveling across the country, yet I think another 

 line of levels should have been taken by way of verification 

 before any conclusion should have been adopted as to com- 

 parison of tides. Such verification would prove the correct- 

 ness of the relative levels of the several bench-marks, which 

 might be applied to further observations on the tides, and the 

 levels extended to other places. It appears that the operator 

 took every care to observe correctly the levels, and to prove 

 them by leveling back over the line, in which the difference 

 of results are so trifling as not to excite notice, if it had not 



