257 



correct. Several tide tables for London are annually published ; but 

 they vary considerably from one another. The method generally 

 practised in England for the construction of tide tables for other 

 places, has been to add or subtract some constant quantity, according 

 to the place, assuming as a basis the tide tables either of London or 

 of Liverpool 5 but this assumption of a constant difference is shown 

 by the author to be, in various instances, incorrect. Much, therefore, 

 remains to be done, before we can hope to arrive at a scientific solu- 

 tion of this problem. 



The author then proceeds to examine the empirical laws of the 

 tides of the port of London, deducible from the records of the nine- 

 teen years of observations which have been discussed by Mr. Dessiou, 

 under the direction of Mr. Lubbock, and which include 13,073 ob- 

 servations. His first object is to determine the manner in which the 

 time of high-water is affected by the following conditions, namely, the 

 right ascensions, declinations and parallaxes of the sun and moon ; 

 for which purpose he considers at some length, first, the establish- 

 ment ; secondly, the semimenstrual inequality ; thirdly, the correc- 

 tions for lunar parallax ; fourthly, the lunar declination ; and lastly, 

 the solar parallax and declination. He next discusses the empirical 

 laws of the height of high-water ; which he observes will be affected 

 in the same manner as the periods of the tides, by a semimenstrual 

 inequality, by corrections for lunar parallax and declination, and by 

 a solar correction ; and concludes by giving a formula for computa- 

 tion which comprehends all these elements. He then enters into a 

 comparison of the results thus obtained with the theory of Daniel 

 Bernoulli, according to which the waters of the ocean assume nearly 

 the form in which they would be in equilibrium under the actions of 

 the sun and moon, on the supposition that the pole of the fluid sphe- 

 roid follows the pole of the spheroid of equilibrium at a certain angular 

 distance - } and that the equilibrium corresponds to the configuration 

 of the sun and moon, not at the moment of the tide, but at a previous 

 moment, at which the right ascension of the moon was less by a 

 constant quantity. The author thinks, however, that it would not be 

 safe to attempt to deduce from the preceding investigations any ge- 

 neral views concerning the laws of the tides, for it is not likely that the 

 discussion of observations at any one place should exhibit clearly the 

 true principles of the theory, especially as, in the present case, it so 

 happens that the phenomena of the tides at London are in some 

 measure masked by a curious combination of circumstances, namely, 

 by the mouth of its river being on the side of an island, turned away 

 from that on which the tide comes, and so situated that the path of 

 the tide round one end of the island is just twelve hours longer than 

 round the other. 



In consequence of the time required to transmit to any port the 

 general effect of the tide-producing forces being different from the 

 time required to transmit to the same port the effects of particular 

 changes in these forces ; or, in other words, from the epochs of the 

 changes due to parallax and declination being different from the epoch 

 of the semimenstrual inequality, it follows that although the general 



