GO 
MR. LUBBOCK ON TIDE OBSERVATIONS. 
I have ascertained that Bernoulli’s expressions present a very remarkable accord- 
ance with observation. But it must be recollected, that the phenomena of the tides 
at London and Liverpool cannot be considered as depending (mechanically) upon 
the coordinates of the sun and moon at the transit immediately preceding the times 
of high water ; and if I had taken in my discussions a transit more remote, the law 
of the intervals would not have been the same. This difference in the law of the in- 
tervals depends upon the difference in the intervals between the successive transits of 
the moon. Hence the law of the intervals, when the discussion is instituted with re- 
ference to the transit immediately preceding the time of high water, whether at 
London, Liverpool, or Brest, depends partly upon the phenomena as deducible from 
Bernoulli’s expressions, and partly upon the law of the intervals between the 
moon’s successive transits, which latter interval may be considered roughly as de- 
pending upon her parallax and declination. For practical tables intended to serve 
in predicting the phenomena, this is of no consequence; but in order safely to com- 
pare the results of theory with those of observation, it is absolutely necessary first to 
obtain the law of the changes in the moon’s motion, which may easily be done. This 
consideration does not apply to the heights. 
I have little doubt from comparisons which I have made, and which I mean to ex- 
tend, that the results of observation present a very remarkable agreement with Ber- 
noulli’s theory, and with the formulae in p. 57, by which this theory is approximately 
represented. In this comparison, however, it cannot be expected that the phenomena 
at any given place are the same (as Laplace seems to imply*) as would belong to that 
geographical latitude, if the figure of the ocean were that of a perfect spheroid, and 
were not intersected by continents. I apprehend that the inequalities of the tides at 
Brest are produced mechanically some time previous, and are not due to the position 
of the luminaries (in a certain sense) at the time of high water. 
Mr. Deacon has furnished me with a continuation of Tables A, B, C, D, for the 
last six months of the year 1835, which serve to show the degree of congruity in the 
observations at the London and St. Katherine Docks with each other and with the 
predicted tides in the British Almanac. 
“ Si le port a une latitude, ces pleines mers pourraient etre fort differentes ; et quand la declinaison des 
astres est dgale a l’obliquite de l’ecliptique, la maree du soir a Brest serait environ huit fois plus grande que 
celle du matin .” — Mecunique Celeste, tom. v. p. 148. 
