British Association for the Advancement of Science. 3 



travel from one place to another at the rate of fifteen miles an 

 hour, while one of ten feet deep would proceed at the rate of only- 

 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 crea- 

 tion of a tidal Bore in some places was also accounted for on the 

 same principles ; 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. 



Magnetical Observatory at Dublin. — The Magnetical Observa- 

 tory now in progress at Dublin, is situated in an open space in the 

 gardens of Trinity College, and sufficiently remote from all dis- 

 turbing influences. The building is forty feet in length, by thirty 

 in depth. It is constructed of the dark-colored argillaceous lime- 

 stone, which abounds in the valley of Dublin, and which has been 

 ascertained to be perfectly devoid of any influence on the needle. 

 This is faced with Portland stone ; and within, the walls are to be 

 studded, to protect from cold and damp. No iron whatever will 

 be used throughout the building. With reference to the materi- 

 als, Prof Lloyd mentioned, that in the course of the arrangements 

 now making for the erection of a Magnetical Observatory at Green- 

 wich, Mr. Airy had rejected bricks in the construction of the 

 building, finding that they were in all cases magnetic, and some- 

 times even polar. Mr. Lloyd has since confirmed this observation, 

 by the examination of specimens of bricks from various localities ; 

 and though there appeared to be great diversity in the amount of 

 their action on the needle, he met with none entirely free from 

 such influence. 



The building consists of one principal room, and two smaller 

 rooms, — one of which serves as a vestibule. The principal room 

 is thirty-six feet in length, by sixteen in breadth, and has projec- 

 tions in its longer sides, which increase the breadth of the central 

 part to twenty feet. This room will contain four principal instru- 

 ments, suitably supported on stone pillars : viz. a transit instru- 

 ment, a theodolite, a variation instrument, and a dipping circle. 

 The transit instrument (four feet in focal length,) will be stationed 



