352 Royal Society : Report of the Council: 



almost perfect accordance with the observed inequalities in the 

 heights and times of the tides which are due to the changes in the 

 moon's parallax. This was a most important step in the connexion 

 between theory and observation, and has been found to apply, to a 

 considerable extent, to all tlie periodical inequalities of the tides, 

 though very different epochs are required for different inequalities. 

 Thus Mr. Whewell has shown that the diurnal inequality in the 

 heights of high and low water, which is due to the change in the 

 moon's declination, would require to be referred to the lunar transit 

 four days preceding. 



•But though the formulae furnished by theory can be thus adjusted 

 to represent generally the results of observation for any assigned 

 station, yet our theory is quite incompetent to assign the physico- 

 mathematical grounds upon which such adjustments are made: the 

 complete solution of such a problem would probably require a know- 

 ledge of the laws of hydrodynamics much beyond that which we 

 now possess. 



The first memoir which was published by Mr. Whewell was an 

 " Essay towards a first approximation to a map of cotidal lines," and 

 appeared in our Transactions for 1 8S3. 



By cotidal lines, Mr. Whewell means those lines which may be 

 drawn through all those points of the ocean which have high-water 

 at the same moment of absolute time. 



By analysing the movements of the tides as determined by the most 

 simple considerations of the laws of fluid motion in open seas and in 

 channels, and by explaining the circumstances of their convergence 

 or divergence, their interference with each other, their retardation 

 in shallow water, and their consequent tendency to sweep round the 

 coasts and to approach them almost perpendicularly ; and further, 

 by discussing very carefully all the materials which nautical surveys 

 and books of navigation could furnish him, Mr. Whewell was en- 

 abled to construct a map, which not only represented the general 

 circumstances of the tides of the coasts of Great Britain, but like- 

 wise the movement of the great tidal wave, on the coasts of Europe, 

 in the Atlantic Ocean, in the Indian seas, and on the coasts of New 

 Zealand. 



It was with a view to correct this first approximation to a map 

 of cotidal lines that Mr. Whewell procured a very extensive series 

 of observations to be made on the coasts of Great Britain and Ire- 

 land at 547 stations of the Coast Guard for an entire fortnight in 

 June, 1834-. These observations were repeated in June, 1835, and 

 were accompanied by simultaneous observations made by the great 

 . maritime powers of Europe and North America, at the request of 

 the Government of this country, at various stations on their coasts. 

 The immense mass of observations, thus furnished, were reduced, 

 under Mr. Whewell's directions, at the expense of the Admiralty, 

 and some of the results, which are extremely important and in- 

 teresting, have been communicated by him to the Royal Society in 

 two Memoirs in our Transactions for 1835 and 1836. The last of 

 these Memoirs was accompanied by a second map of the cotidal 



