Royal Society. 381 



In section fourth, the author treats of certain extreme cases of diur- 

 nal inequality ; particularly those which produce the phaenomenon of 

 a single tide in the twenty-four hours : such as that noticed by Capt. 

 Fitzroy at King George's Sound, on the south coast of New Holland j 

 and that of Tonquin, referred by Newton to the interference of two 

 tides arriving by different channels, but probably owing to the ope- 

 ration of the same law as that which gives rise to the diurnal ine- 

 quality. 



Jn section fifth, the author considers the subject of the mean height 

 of the sea j that is, the height midway between low water and high 

 water each day : and arrives at the result that it is very nearly con- 

 stant. 



March 16. — A paper was read, entitled, "On the Tides." By 

 John William Lubbock, Esq., F.R.S., &c. 



Since the author presented his last paper on the tides to the Society, 

 his attention has been directed to ascertain the three following points: 

 namely, 1st, Whether, from the discussion of the Liverpool observa- 

 tions with reference to a previous transit, these observations present 

 the same kind of agreement with Bernoulli's theory as those of Lon- 

 don : 2ndly, Whether, by taking into account a greater number of 

 observations, the results given in his last paper remain sensibly un- 

 altered : and 3rdly, Whether the establishment oi the Port of London 

 varies sensibly in different years; and whether the removal of the old 

 London bridge has occasioned any difference. In order to elucidate 

 these points, he procured the assistance of Mr. Jones and Mr. Ruwssell 

 to compute numerous tables; employing for that purpose a further 

 sum of money placed at his disposal with this view by the British 

 Association for the Advancement of Science. The results contained 

 in the tables here presented, are all laid down in diagrams, on the 

 same plan as those contained in his last paper, by which means they 

 are much more readily understood. The author finds that the semi- 

 menstrual correction for the interval at Liverpool presents the same 

 agreement with observation as had been before noticed -, while the 

 form or law of the semi-menstrual correction for the height is also the 

 same as that indicated by the observations ; but in order to render the 

 agreement complete it would be necessary to change the epoch, or to 

 make a slight movement of the theory-curve in the diagrams. This 

 remarkable difference also obtains in the London semi-menstrual cor- 

 rection for the height. 



The calendar month inequality at Liverpool, considered as result- 

 ing implicitly from the corrections due to changes in the declinations 

 of the luminaries, and in the sun's parallax, agrees generally with Ber- 

 noulli's theory, and with the results deduced from the London obser- 

 vations given in the author's last paper. 



The author finds that the Establishment of the Port of London has 

 been subject to changes even since the beginning of the present cen- 

 tury, and he notices the difficulty of predicting the time of high water 

 with accuracy unless these changes can be accounted for. He also 

 cites a very ancient Tide Table, from which it would appear that for- 



