886^ Proceedings of the British Association, 



paring the tide with the nearest preceding transit. But, in truth, 

 we ought not to refer the tide to such a transit, because we know 

 that the tide of our shores must be produced in a great measure by 

 the tide which revolves in the Southern Ocean, and which every 

 half day sends off tides along the Atlantic. The tide, therefore, 

 which reaches Bristol, is the result of a tide wave, which was pro- 

 duced by the action of the sun and moon at some anterior period. 

 It is found, that if at Bristol we refer each tide to the transit of 

 the moon, which took place about forty-four hours previously, we 

 do obtain an accordance of the observations with theory in the fea- 

 ture above described, — that although the moon's force alters by the 

 alteration of her declination, the defect of the lunitidal interval for 

 a three hours' transit of the moon is equal to the excess of that in- 

 terval for a nine hours' transit. And thus, in this respect at least, 

 the tide at Bristol agrees exactly with the tide which would be pro- 

 duced, if, forty-four hours before the tide, the waters of the ocean 

 assumed the form of the spheroid of equilibrium due to the forces 

 of the moon and sun, and if this tide were transmitted unaltered to 

 Bristol in those forty-four hours. 



Wednesday Aug. 24. 



Section A — Mathematical and Physical Science. 



The first paper read was by Mr W. Snow Harris, " On some 

 phenomena of Electrical Repulsion." 



Professor Challis read his " Supplementary Report upon the Ma- 

 thematical Theory of Fluids." 



Professor Stevelly gave his " Illustration of the meaning of the 

 Doubtful Algebraic Sign in certain formulae of Algebraic Geome- 

 try." 



Professor M*Cullagh made a communication respecting the laws 

 of Double Refraction in crystals of quartz. 



Mr R. Addams then made a communication on the Interference 

 of Sound, and illustrated his subject by several experiments. 



Section B. — Chemistry and Mineralogy. 



Dr Daubeny read an interesting report on the present state of 

 our knowledge with respect to Mineral Waters. 



Mr Mushet exhibited some specimens of metallic iron prepared 

 by exposing the iron-ore to long continued heat, with a small quan- 



