126 Mr. Lubbock ofi the Tides ifi the Port of London. 



times of high water, employing for the purpose no less than 

 nine thousand observations of those made at the London Docks 

 in the course of twenty-five years. 



It is found that the times of high-water calculated from the 

 table given in the Annuaire, would differ widely from the ob- 

 served time ; but by applying the formula from which this 

 table was deduced with alterations in the constant quantities, 

 according to Laplace's theory, the mean of the observed times 

 agrees with the time calculated, with an exactness which 

 amounts almost to identity, as will be seen by the following 

 table, which results from the expression, 



m P3 

 — TSTT sin 2 (^-^' —A. + V) 



tan 2 (fi'-A') = '^ 



1 4. "'■^ cos2 (^-^'- A +V) 

 m' P'3 



in which equation P is the parallax of the sun. 



fl hour-angle of the sun, at the time 



of high water. 



m mass of the sun. 



The same quantities dashed refer to the moon. 

 X and X' are constants depending upon the local circum- 

 stances of the port, and their values for the London Docks 

 deduced from all the tides observed by day during twenty-five 

 years are, X' = 1 hour 32 minutes, X— a' = 2 hours. 



The logarithm of "'' ■ ■ deduced from the same observa- 



o m r' 3 



tions is 9-52452. 



If, according to M. Damoiseau {Memoires des Savans 

 Eti-angers : Theorie de la Lune\ vol. i. p. 502, the mass of the 



moon be equal to the mass of the earth divided by — , and the 



moon's mean horizontal equatorial parallax be 34'3l"'73, page 

 569 ; and if, according to Laplace, Exposition du Si/steme du 

 Monde, page 12, the sun's mean parallax be 26"-54, or 8"'59; 

 and if, according to the same work, page 209, the mass 

 of the eardi be equal to that of the sun divided by 354936 



\qct. .^ULEL — 9-62170. The value of the same quantity de- 



duced by Laplace from the observations of the tides at Brest, 

 is 9-62833. The column headed " Observed," is the mean of 

 about nine thousand observations; in which, as they were made 

 at all seasons of the year, the variations in the declinations of 

 the sun and moon and the equation of time can have no per- 

 ceptible influence. The inequality o( variation in the moon's 



parallax 



