Remarks on some Tide Observations. 135 



of the mean height of the sea, may be operated on in a regular 

 way by whatever causes it to vary at different periods : but 

 I am not aware that any observations have yet been made for 

 the purpose of determining the recurrence of such variations, 

 or for ascertaining their causes ; and until this be done, no 

 mean tide- level could be determined on. But, after all, such 

 standard level must have reference to some fixed or bench mark 

 in order to make it useful, and could only be applied to one 

 neighbourhood, as it could not be depended on with reference 

 to tides at any distant part of the coast, which may be exem- 

 plified by a reference to the tides between the Land's-end and 

 King- Road ; and although this example may be taken as al- 

 most an extreme case, nevertheless it will serve the better to 

 elucidate the uncertainty of tide-marks. 



" It must be evident that the particular formation and trend- 

 ing of the coast as connected with the set of the tide will tend 

 to alter the elevation of the high-water as well as of the low- 

 water marks. The Bristol Channel, from its form narrowing 

 upwards to the Severn, causes the tidal wave to rise much 

 higher than at any other part of the English coast, for it may be 

 considered that the tides at the flood have a tendency to rush 

 from the Atlantic into the mouth of this channel with about the 

 same velocity as through the inlets to the English Channel 

 and the Irish Sea ; but in the Bristol Channel there is not the 

 same proportion of space as compared with the breadth of 

 the entrance ; hence in their course upward, being confined 

 by the approximation of the shores, they are raised to a height 

 increasing as the breadth lessens, until they attain sufficient 

 elevation for the gravity of the water to counterbalance the 

 impulse of the tide. 



" The sea at ordinary spring tides rises and falls about 4-5 

 feet at King- Road, yet the low water there appears to be some 

 feet above the low water of the ocean, as the great influx of 

 the Severn at such tides occasions a great quantity of water to 

 be coming down even at the return of the flood, so that at the 

 time of low water below| the Holmes Isles, the down tides run 

 with such rapidity at King- Road as to indicate a great fall, 

 and consequently there is a considerable rise in the tide be- 

 fore it meets the level of the water there ; but it must be re- 

 collected, that then there will be some fall in the water from 

 the Holmes to King- Road. 



" At Ilfracombe, about the same time as I observed the 

 tides at King-Road, the rises and falls were taken by my par- 

 ticular directions, and showed the ordinary spring tides there 

 to rise and fall about 30 feet, and the ordinary neaps about 

 14- feet. 



