562 
fages in ancient authors, which attribute 
the caufe of it to the attra€tion of the hea- 
venly bodies; but thefe ideas, which were 
only fimple, rude notions, remained unim- 
proved tillthe time of Newton; as true 
knowledge cannot be obtained until we 
are advanced far enough to fubmit it to 
analyfis. and make it the fubject of a rigo- 
rous calculation; it is only, properly 
fpeaking, at this period that the {cience 
commences. 
The moft fimple obfervations, and even 
thofe the moft circumfcribed to one fpot, 
ought, long before the time of Pitheas, 
to have induced a fufpicion that the tides 
are regulated by the moon; all the inha- 
bitants of the coafts of the ocean might 
have been readily convinced of it. Indeed, 
every thing announces this fact with the 
fame evidence as the return of the feafons. 
We cannot beftow great encomiums on the 
authors who have fpoken of it the firft 5 it 
was not with them, properly fpeaking, a 
difcovery, nor even an obfervation at all 
profound. Till Newton, the world was 
completely ignorant of the true caufe of 
this wonderful phenomenon. Till his 
time, men wandered in vain hypothefes 
and were far from fuppofing that it was 
fubjeét to the fame law as that which 
regulates and determines the movements 
of the different parts of the planetary 
fy tem. 
Notwithftanding this profound igno- 
rance of caufes, navigation, that art which 
lays all others under contribution, ‘has 
early derived great advantages from the 
fa&ts afcertained. It was fufficient to ob- 
ferve, that the daily ftop of the tides is 
fenfibly uniform; that they return at the 
fame hour every fortnight, and that the 
higheft tides take place at the time of the 
new andfull moon. It was fufficient from 
a knowledge of thefe data, to be able to 
calculate the time of bigh tide, with a pre- 
cifion that was fatisfatory and which was 
perfectly adequate to the wants of the firft 
ages. 
Now that we have no longer any thing 
to wifh for, with regard. to the theory of 
the flux and reflux of the fea; and that, 
thanks to the progrefs of analyfis, fince 
Newton, all its details and effeéts have 
been calculated with the precifion requi- 
fite in the obfervations of the celeftial phe- 
nomena; it becomes an incumbent duty 
to multiply and perfe& thefe obfervations, 
not in order to confirm a theory which.no 
longer ftands in need of demonftration, 
but in order to eftablifh and determine a 
Proceedings of learned Societies. 
[ July 1 9 
number of delicate points in the fy%em of 
the world; and likewife to account fatis- 
factorily for certain apparent anomalies 
remarkable in particular regions of the 
gicbe, and to affign the real caufe of them. 
It is already known, that thefe anomalies 
are a confequence of the general move- 
ment, modified, however, by local cir-_ 
cumftances; but we ftill want to be able 
to afcertain the influence of thofe circum- 
ftances in every part; and this can only be 
done by good obfervations. 
Befides, the fafety of navigation is 
clofely conneéted with thee obfervations, 
and with the refults that neceffarily flow 
from them; for, confidering the great 
draught of water in veflels, it is of no 
{mall importance to calculate with precifion 
the exact hour of full tide, not only in the 
interior of the ports, but ftill n_ re parti- 
cularly, in the difficult paffages that lie 
towards their mouth, where ve. els can ~ 
only pafs fecurely at the time of high 
water. The navigation muft be regulated 
in fuch a manner, as to arrive in thefe dan- 
gerous paflages, precifely at the infant 
when they ceafe to be fo; that is to fay, 
about the time of high water. The whole 
coafting navigation ftands in need of very 
exact documents with refpeét to the move- 
ment of the tides: and it is now high time 
to fet about this enterprize, fo that the 
marine and commerce may enjoy the ad- 
vantages refulting from the aétual ftate of 
our information. Public utility is the fole 
end of the meditations and refearches of 
geometrical] naturalifts. 
At the beginning of the laft century, 
the Academy of Sciences perceived the — 
urgent neceflity of having accurate obfer- 
vations; it prefented to M. le Comte de 
Pontchartrain, then at the head of the 
department of the marine, a memoir, in 
the form of infructions, relative to the 
neceflity of deputing intelligent and capa- 
ble perfons to obferve the flux and reflux 
of the fea, and the method that ought to 
be purfued in order to make the faid obfer- 
vations. The Fathers Gouge and Lahire 
drew up the above memoir, agreeably to 
the views of the Academy. The Minifer 
affigned this labour to the profeffors of na- 
vigation, eftablifhed in the refpective ports, — 
and the academy received many feries of — 
obfervations, the principal of which were 
thofe made at Dunkirk and at Havre, du- 
ring the years z701 and 17023 the former 
by M. Baert, and thofe at Havre by M.- 
Boffaye du Bocage; both profeflors of na- 
vigation, 
Caffini, 
