10 EIGHTH RKPOKT — 1838. 



different high watei-s ; that is, till a proper discussion of tide 

 observations is combined with a system of leveling operations. 



I may add that this result is certainly erroneous ; for it gives 

 the high water in Bridgewater Bay only two feet higher than on 

 the south coast of Devon ; whereas by our observations, which 

 certainly cannot err a foot, the former level is at least fourteen feet 

 higher than the latter. The difference, which is perhaps not to 

 be wondered at in rough leveling such as that performed in a 

 preparatory survey for a canal, is twentyfold greater than our 

 operations, carried backwards and forwards, and only differing 

 one or two inches in the result, allow us to consider as possible. 



19. We may observe, in conclusion, that the result of our 

 operations, namely, that the mean tide in different points of the 

 coast is at the same level within a few inches, is of no small 

 practical value. For this being so, the level of any place within 

 a moderate distance of the coast may be determined, for the 

 purposes of canals or railroads, or any similar undertakings, 

 with reference to the level of places hundreds of miles distant, 

 by taking a fortnight's observations of high and low water, and 

 then leveling a few miles into the interior of the country. 



20. It may perhaps be said that the conclusions thus stated de- 

 pend upon a single comparison ; that of the south shore of the 

 Bristol Channel, with the north shore of the English Channel. 

 When itis recollected that there are, omitting thesmaller flexures, 

 some hundreds of miles of coast between the two extremities of 

 our line, and that the tides at the extremities differ as forty feet 

 and twelve feet, I think it is impossible not to allow great value 

 to the result ; the operations being, as I conceive, of unim- 

 peachable accuracj'. But I am at the same time quite ready to 

 admit that it would be highly desirable to have the result corro- 

 borated by other comparisons of the same kind, especially by a 

 comparison of the east and west shores of England. For this 

 purpose it might be desirable to carry a level line from Bristol, 

 which is already connected with our operations, to London. The 

 expense of this, if performed in the same manner as that which I 

 have described, would be great ; but it appears to be worth con- 

 sideration, whether this expense might not be much reduced by 

 observing the waters of existing canals. 



21. I will add, that such an extension of our level to London, 

 and in like manner to Plymouth, Liverpool, and other principal 

 ports of the empire, would be desirable in another view. As I 

 have already said, we cannot speak with accuracy of any level 

 except a conventional one ; and as each of these ports has its 

 own tide scales to which the rise and fall of the sea's surface is 

 referred, it would be desirable to compare the absolute position 



