320 Proceedings of the British Association, 



clination of the Moon and of the Sun, and in reference to local, 

 and what may in one sense be called accidental causes, as storms, 

 &c. Of this latter, one of the most curious, as well as important, 

 is the effect of the pressure of the atmospheric column. The au- 

 thor stated, that M. Daussy had ascertained, that at the har- 

 bour of Brest a variation of the height of high-water was found to 

 take place, which was inversely as the rise or fall of the barome- 

 ter, and that a fall of the barometer of 0.622 parts of an inch, was 

 found to cause an increase of the height of the tide, equal to 8.78 

 inches in that port. To confirm this interesting and hitherto un- 

 suspected cause of variation, had been one principal object of the 

 researches of the learned gentleman ; and, at his request, Mr Des- 

 siou had calculated the heights and times of high-water at Liver- 

 pool for the year 1784, and compared them with the heights of the 

 barometer, as recorded by Mr Hutchinson for the same year : and 

 by a most careful induction, it had turned out that the height of the 

 tide had been on an average increased by one inch for each tenth of 

 an inch that the barometer fell, cceteris paribus ; but the time was 

 found not to be much, if at all affected. Mr Lubbock then pro- 

 ceeded to examine the semi-menstrual declination and parallax cor- 

 rection, and stated that the result was a remarkable conformity be- 

 tween the results of Bernouilli's theory, and the results of observa- 

 tions continued for nineteen years at the London Docks. But to 

 render the accordance as exact as it was found to be capable of be- 

 ing, it was necessary to compare the time of the tide, not with that 

 transit of the Moon which immediately preceded it, but with that 

 which took place about five lunar half days previously. To ex- 

 plain this popularly, Mr Lubbock stated, that, however paradoxical 

 it might appear to persons not acquainted with the subject, yet 

 true it was, that, although the tide depended essentially upon 

 the Moon, yet, any particular tide, as it reaches London, would 

 not be in any way sensibly affected, were the Moon at that in- 

 stant, or even at its last transit, to have been annihilated ; for it 

 was the Moon as it existed fifty or sixty hours before which caused 

 the disturbance of the ocean, which ultimately resulted in that 

 tide reaching the port of London. The author then exhibited 

 several diagrams, in which the variations of the heights of the 

 tide, as* resulting from calculations founded upon the theory, 

 were compared with the results of observations. The general 

 forms of the two curves which represented these two results, cor- 

 responded very remarkably; but the curve corresponding to the 

 actual observations, appeared the more angular or broken in its 



