On the Tides. 119 
terminating in a very large road, at the extremity of which the 
port has been built. Thus the irregularities of the motion of 
the sea are considerably weakened before they reach the port, 
very nearly in the same manner as the oscillations produced in 
the barometer by the irregular motion of a vessel, are diminished 
by a contraction in the tube of this instrument. In other re- 
spects the tides being considerable at Brest, the casual varia- 
tions occasioned by winds form only a small part of them. It 
may also be remarked in the observations made of these tides, 
however few there may be of them, that a great regularity pre- 
vails which is not altered by the ‘little river, which loses itself 
in the immense road of this port. Struck with this regularity, 
I solicited government to order a new course of observations to 
be made at Brest, during an entire period of the motion of the 
nodes of the lunar orbit. They had long been wished for. ‘These 
new observations are dated from the Ist of June 1806, and since 
that period they have been continued uniuiterruptedly to this 
day. There is still, however, much wanting. ‘They relate 
neither to the same part of the port, nor to the same scale. The 
observations of the first five years have been made at the place 
called La Mature, the others were taken near the bason. I 
observe that this change has produced only slight differences ; 
but it would have been better, undoubtedly, if all the observations 
had been made at the same place and upon the same scale. It 
is time, indeed, that phenomena of this nature should be ob- 
served with the same care as those of astronomy. 
In these new observations | have considered those of the year 
1807 and of the seven subsequent years. In each equinox and 
in each solstice I have chosen the three syzygies and the three 
quadratures nearest to this equinox and this solstice. In the 
syzygies I have taken the excess of the high water of the evening 
above the low water of the morning of the day which precedes 
the syzygy, of the day of the syzygy, and of the four following 
days, because the highest tide happens about the middle of this 
interval. I have made a sun of these excesses corresponding 
to each day, by doubling the excesses which relate to the inter- 
mediate syzygy, or that nearest to the equinox or the solstice. 
By this means the effects produced by the variation of the di- 
stances of the sun and of the moon from the earth are destroyed: 
for if the moon were, for example, towards its perigeum in the 
intermediate syzvgy, it would be near its apogeéum in the two 
extreme syzygies. The sums of the excesses thus obtained are, 
therefore, very nearly independent of the variations of the mo- 
tion and of the distances of the heavenly bodies. There are 
still inequalities of the tides, different from that inequality, 
whose period is about half a day, and which in our ports is 
H 4 much 
