180 



his elaborate discussion of the tides of Brest, executed by M. Bon- 

 nard, has verified this accordance to a high degree of precision ; and 

 the recent researches on the tides, by Mr Lubbock and Mr ^T^'hevvell, 

 may be considered as having rendered the celestial mechanics 

 of the tide as perfect as any other department of Astronomy, the 

 errors of prediction being now reduced within the limits of the er- 

 rors of observation ; so that Mr Lubbock has stated tliat he does 

 not look forward to any material improvement in this department 

 of our knowledge. 



But our acquaintance with the terrestrial mechanism of the 

 tides is in a very different condition. In reference to the pheno- 

 mena of this department, Laplace has said, in the third chapter of the 

 fourth book of the Mecanique Celeste, and he repeats the opinion 

 in tlie first chapter of the thirteenth book, at a much later date, 

 where he says : " Que les circonstances accessoires produisent des 

 varietes considerables dans les hauteurs et dans les heures des 

 marees des ports meme tres rapproches ;" and then he adds, " II 

 est impossible de soumettre an calcul ces varietes, parceque les cir- 

 constances dont elles dependent, ne sent connues." Mr Lubbock, 

 in like manner, speaking of the fluctuation of the establishment, 

 says, " This perplexing fluctuation presents an insuperable obstacle 

 to extreme accuracy in tide predictions, until it can be explained ; 

 at present we are only left to conjecture respecting the cause." 

 And Mr Whewell says, in 1837, " I cannot conclude this paper 

 without again pointing out that a great number of curious facts 

 in fluid motion ai'e establislied in tliese Tide Researches, of which 

 it may be hoped the theory of hydrodynamics will one day be able 

 to render a reason." 



In 1834, the author of this paper had determined the law of the 

 interference of a certain species of wave in the resistance of fluids, 

 and this species of wave appeared to present very striking analo- 

 gies to the tide-wave. In 1835, Mr Whewell expressed his decid- 

 ed conviction of their similarity, and Mr Robison and Mr Russell 

 were, in 1836, appointed a Committee of the British Association 

 to investigate the subject. The Report of these observations was 

 given to the British Association in 1837 ; but as the observations 

 themselves are not necessarily coimected with the particular con- 

 clusions whicli may be drawn from them, these conclusions, at 

 which the autlior had arrived, were made the subject of a separate 

 paper to this Society. 



