18 REPORT— 1839. 



ments obtained by bisecting the times at which the water is at 

 three-fourths the height of H. W. above the level of mean water, 

 during the rise or the fall of each tide. The corrections are ar- 

 ranged according to the hour of the moon's transit, and repre- 

 sented on a scale of forty minutes to an inch. The transit of the 

 moon here employed is not the one immediately preceding the 

 H. W., but, in the first figures, it is the one a day and a half 

 previous to that which precedes the H. W. ; that is, the transit 

 B of Mr. Lubbock. In the latter figures, constructed from 

 thirty-eight hours' anterior epoch, an epoch or transit is em- 

 ployed, interpolated midway between B and C, which appears 

 in some respects to give better results than either of those two 

 transits. 



The curves entitled displacement of Summits express the dif- 

 ference of time of H.W. as actually observed, and as inferred by 

 bisection of the interval of equal altitudes just described. This 

 difference shows itself in the displacement of the summits of the 

 curve, which exhibits the rise and fall of the water on Mr. Bunt's 

 machine. It is a remarkable and not very easily explicable cir- 

 cumstance, that this displacement appears to be more affected 

 by solar parallax than by any other element. When the dis- 

 placement is such as to accelerate the time of H. W., the fall 

 of the tide is less rapid, and when such as to retard the time of 

 H.W., the fall is more rapid than the rise. 



W. Whewell. 



