Proceedings of the British Association. 363 



than the mean when the moon passes nine hours after the sun ; and 

 the quantity by which the hmitidal interval is less than the mean 

 when the moon is three hours after the sun, is exactly equal to the 

 quantity by which the lunitidal interval is greater than the mean 

 when the moon passes nine hours after the sun. And this equality 

 of the defect and excess of the interval at three hours and at nine 

 hours of the moon's transit, is still true where the moon's force al- 

 ters by the alteration of her parallax or declination. Now we are 

 to inquire whether this equality of excess and defect of the interval 

 in all changes of declination, &c., is exhibited by observation. It 

 appears at first sight, that the equality does not exist; that is, if we 

 obtain the lunitidal interval by comparing 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 oIT tides along the 

 Atlantic. The tide, therefore, which reaches Bristol, is the result 

 of a tide wave, which was produced by the action of the sun and 

 moon at some anterior period. It is found, that if at Bristol we re- 

 fer each tide to the transit of the moon, which took place about forty 

 four hours previously, we do obtain an accordance of the observa- 

 tions with theory in the feature 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 interval for a nine hours' transit. And thus, in 

 this respect at least, the tide at Bristol agrees exactly with the tide 

 which would be produced, 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 trans- 

 mitted 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." 



Prof. ChaUis read his " Supplementary report upon the mathe- 

 matical theory of fluids." 



Prof. Stevelly gave his " Illustration of the meaning of the doubt- 

 ful algebraic sign in certain formulae of algebraic geometry." 



