MR. LUBBOCK ON THE TIDES IN THE PORT OF LONDON. 
381 
tremely interesting, if the results of the observations at Brest were arranged in 
Tables similar to those which accompany this paper. In a classification of this 
kind it is necessary that the epoch of the phenomena should be defined by the 
minute of the moon’s transit ; the day of the moon’s age is quite insufficient. A 
complete classification of this kind is desirable, because erroneous conclusions 
may be drawn from isolated portions of the curve; and it is necessary, in order to 
ascertain the agreement between theory and the fact, to compare them through- 
out the whole period or extent of the inequality whose effect is considered. 
According to the theory of Bernoulli, and the Tables founded upon it, 
which are given in various works on navigation *, the variation in the interval 
between the time of the moon’s transit and the time of high water, due to 
changes in the moon’s parallax, vanishes or is equal to zero when the moon 
passes the meridian at 2 o’clock or 8 o’clock (or when 0 — — X + X, = 0 or 
180°). This is directly contrary to our observations, according to which the 
variation is the greatest at this age of the moon. See Table XV. 
According to our observations, the time and the height of high water are 
the same, whether the moon’s declination be north or south ; if any difference 
obtain, it must be determined by more delicate means : nor is there any sensi- 
ble difference whether the moon’s transit be superior or inferior, as may be 
seen by Table XIII., where the observations for one month are separated, those 
corresponding to the superior and those corresponding to the inferior transits 
being kept distinct. 
The Tables XV, XVI, XVII, XVIII, XIX and XX are intended to fur- 
nish the means of calculating empirically the time and height of high water, 
taking into account the changes in the different months of the year, and also 
those due to changes in the moon’s parallax and declination. By means of 
these Tables, Mr. Dessiou has calculated the times and heights of high water 
for the year 1826; and, having classed all the observations made at the London 
Docks in that year according to the different winds, has found for each a 
correction, which is given in Table XXI. The variation or correction due to 
the wind depends, of course, also on its rapidity or force ; it appears however 
* I have had occasion in the Preface to my “Account of the Traite sur le Flux et Reflux de la Mer,” 
of Daniel Bernoulli, to point out an error which exists in several Tables of this kind, from the heading 
being reversed ; but this error does not remedy the discrepancy in question. 
