THE TIDES. 219 



wave and gradually contracting like a funnel, the convergence of water causes 

 a very great increase of the range. Hence the very high tides in the Bristol 

 channel, the bay of St. Malo, and the bay of Fundy, where the tide is said to 

 rise sometimes to the height of one hundred feet. Promontories, under certain 

 circumstances, exert an opposite influence, and diminish the magnitude of the 

 tide. The observed ranges are also very anomalous. At certain places on the 

 southeast coast of Ireland, the range is not more than three feet, while at a 

 little distance on each side it becomes twelve or thirteen feet ; and it is re- 

 markable that these low tides occur directly opposite the Bristol channel, where 

 (at Chepstow) the difference between high and low water amounts to sixty feet. 

 In the middle of the Pacific it amounts to only two or three feet. At the Lon- 

 don docks, the average range is about 22 feet ; at Liverpool, 15.5 feet ; at 

 Portsmouth, 12.5 feet ; at Plymouth, also 12.5 feet ; at Bristol, 33 feet. 



A great number of observations of the tides at the port of Brest during the 

 last century were discussed by Laplace in the Mecanique Celeste ; but in order 

 to determine the motion of the tide wave, and separate the general laws of the 

 phenomena from local irregularities, it is necessary to have regular series of 

 observations made at different parts of the ocean. Until very recently, 

 theory may be said to have been in advance of observation ; but of late years 

 the subject has received great attention, and at the present time a more per- 

 fect theory of hydrodynamics appears to be necessary for the physical ex- 

 planation of the phenomena. In 1829, Sir John Lubbock undertook the dis- 

 cussion of the tide observations which are made at the London docks, with the 

 view of obtaining correct tables for predicting the time and height of the tides 

 for the British Almanac. The results, which were published in the Philo- 

 sophical Transactions for 1831, are deduced from a series of upward of thirteen 

 thousand observations during a period of nineteen years, and are of great im- 

 portance, both as affording materials for the construction of tide-tables, and as 

 pointing out the defects of the equilibrium theory, with which they were accu- 

 rately compared. 'In some of the subsequent volumes of the Transactions the 

 author has continued his investigations, and has also published separately an 

 account of Bernoulli's Traite sur le Flux et Reflux, and an elementary trea- 

 tise which appeared in 1839. In the Philosophical Transactions for 1833, Mr. 

 Whewell gave an Essay toward a first Approximation to a Map of Cotidal Lines, 

 which has been followed by a series of interesting papers in the subsequent 

 volumes. Mr Whe well's researches have been chiefly directed to the deter- 

 mination of the following points : First, the motion of the tide wave at differ- 

 ent parts of the ocean ; secondly, the comparison of the observed laws at 

 different places with the theory ; and lastly, the laws of diurnal inequality. In 



1834 the British Association procured an extensive series of observations to 

 be made on the coasts of Britain and Ireland at five hundred and thirty-nine sta- 

 tions of the coast guard. These were repeated at the same places in June, 



1835 ; and at the request of the British government, simultaneous observations 

 were made by the other maritime powers of Europe and the United States. ' 

 The number of stations in America was twenty- eight, extending from the mouth \ 

 of the Mississippi to Nova Scotia ; and the number on the continent of Europe ( 

 one hundred and one, between the straits of Gibraltar and the North cape of , 

 Norway. The results of these observations reduced under Mr. Whewell's su- J 

 perintendence were published in the Philosophical Transactions for 1836 ; and , 

 they are of great importance, not only as affording a far more precise determi- j 

 nation of the progress of the tide wave and the forms of the cotidal line on the < 

 coasts of Europe and North America than previously existed, but as furnishing j 

 more correct data for the construction of the tide-tables. 



Besides the numerous causes of irregularity depending on the local circum- j 



