114 British Association, 



analogous phaenomena of the great tidal wave. In his observations 

 on the River Dee, Mr. Russell found that the tide wave followed pre- 

 cisely the same laws as those in his experimental channel ; that its 

 velocity was exactly proportioned to the square root of the depth of 

 the fluid, that its form changed in the same manner, and the exist- 

 ence of the same law was sufficient to account for the different rate 

 of propagation of different tides between two given places, because 

 a tide of fifteen feel deep would travel from one place to another at the 

 rate of fifteen miles an hour, while one of ten feet deep would only pro- 

 ceed at the rate of twelve miles an hour ; so that if the places were 

 thirty miles apart, the one would receive the former tide two hours 

 later, and the latter tide two and a half hours later than the other. The 

 creation of a tidal bore in some places was also accounted for on the 

 same principles j and it was evident that the means of improving 

 the navigation of tidal rivers might be satisfactorily deduced from 

 these principles. 



Similar observations had been made on the tidal wave of the River 

 Clyde, which was found to move in strict conformity with the laws of 

 the great wave of translation, as determined by Mr. Russell's previous 

 experiments. 



The effect of the wind upon the tidal wave had been eliminated by 

 Mr. Lubbock from the Liverpool observations, and had been denied 

 by Monsieur Daussy in his discussion of the Brest observations. Mr. 

 Robison and Mr. Russell had directed their observations to this also, 

 and had ascertained that its effects were of the most decided character. 

 It was, however, probable that during the ensuing year they would be 

 able to determine the nature and the measure of these effects with 

 still greater precision. 



Mr. Whewell asked several questions of Mr. Russell respecting the 

 method adopted for taking the level of the rivers in the Dee and in 

 the Clyde. — Mr. Russell replied, that the level of mean tide was used 

 in the Dee, and a fixed line was taken for many miles along the 

 Clyde. Mr. Whewell also asked how the depths were taken, and 

 how the agitation arising from the pressure of the waves was deter- 

 mined at various depths. — Mr. Russell replied, that the depths were 

 taken by actual measurement, but that the pressures at various depths 

 had only been taken on the small scale of the models. Mr .Whewell 

 expressed much gratification at the methods of experimenting adopted 

 by Mr. Russell ; and although some of his conclusiona seemed at 

 present to be scarcely reconcileable with the theoretic views held on 

 the subject, yet he anticipated that the utmost advantage would re- 

 sult from researches so ably conducted, and trusted that Mr. Russell 

 would continue and extend them. — Sir William Hamilton fully con- 

 curred in the expressions of approbation which had fallen from Mr. 

 Whewell. 



Prof. Powell read a paper * On Von Wrede's Explanation of the 

 Absorption of Light by the Undulatory Theory.' 



Von Wrede supposes the particles of a transparent body placed re- 

 gularly at equal distances (6), and the ether being diffused between 

 them, a ray of light is propagated directly through the medium, but 



