1804.] 
the apparent diameter of the moon at the 
inftant of high water, and the other the 
declination of the muon, at the fame in- 
ftant, exprefled in degrees and minutes 
only : or it might be fufficient to fill up 
thefe four laft columns with obfervations 
of the tides, on the days of the fyzygies, 
of the quadratures and of the three follow- 
ing days. 
To thefe ten principal columns it would 
be advifeable 10 add a column of particu- 
lar remarks and obfervations, in which 
may be noted the ftate of the atmofvhere, 
elpecially the direétion of the wind and 
its Momentum or force, during the con- 
tinuance of the flood and ebb; the di- 
rection of the tide might be likewife fet 
down, when rifing and falling. Although 
it does not appear indi penfable: to keep 
an account of the height of the barometer 
and of the degree of the thermometer ; it 
would, however, be of fervice were the 
obfervators to no‘e down, whenever they 
can, thefe two elements in their journal 
of obfervations. 
The primary obje& of the obfervarors 
fould be to eftablith a metrical fcale of 
the tides. Each individual thould choole 
in bis own neighbourhood, a fituation the 
moit convenient and accefflible; above all, 
care fhould be taken, that the zero of the 
{cale fhould never be left dry, even in the 
lowelt tides, 
Yourcoinmiffioners are of opinion, that, 
in the maritime departments, the place of 
oblervation ought to be out of the limits 
of the port, in order to avoid the embar- 
raffments infeparable from great commer- 
cia] movements and operations ; and to 
fecure a communication with the place 
during the night. They likewife think, 
that, in general, the exterior of the port 
is More proper than the interior, to pro- 
eure good oblervations ; in confequexce, 
they propofe that at Breft, the metrical 
fcale fheuid be eftablithed in the roads or 
outer harbour, near to the obfervatory, 
and that the obfervations be included 
' smong the functions of the director or 
fub-direStor of the obfervatory. 
In places where the tides rife to fuch a 
height, that veflels of the firft magnitude 
may pals, without danger, through paf- 
fages that were dry fome hours before, 
as is the cafe at St. Maloes, and at Gran- 
ville, it will not be always ealy to procure 
a icale proper to mark down high and low 
water. In this cafe, the obfervator fhould 
fet apart two portions of the {cale, one to 
alcertain the time of high water, and the 
other of low water; and by taking an ac- 
curate level, he fhould determine how far 
Priceedings of Learned Societies. 
(137 
thé zero of the fir {cale is elevated above 
the zero of the fecond. ‘This laft method 
is highly advantageous, and is even indii- 
penfable in fituations where the fea leaves 
a large traét of dry land. 
The obfervaters fhould ufe their bet 
endeavours that the fcales may be fixed 
and permanent: of courle, they fhould 
eltablifi them upon the jetties, or on par- 
ticular points of the fortifications, and in 
cafe of necellity upen rocks: they fhould 
take care to fhelter them as much as pol- 
fible, in order that the great {welling and 
foam of the fea, in certain cafes, may not 
prove detrimental to the prectfion of the 
obfervations and render them too income. 
modious. , 
The obfervations made in the years 
yor and 1702, by M. Braert, furndha 
commedious apparatus, made ule of by 
that proteflor, to diminifh the effect of the 
efeillations; and which apparatus has 
been fince ufed at Breft in the later obs 
fervations that have been before alluded to. 
This apparatus confilts of a {quare pipe 
formed of tour plates or pieces open at the 
bottom, and fhat at the top by a cover 
or lid, pierced through with a hole in the 
middle. This pipe was placed vertically, 
firongly held togetaer and built round with 
a turret, to fheiter the obfervator, and to 
enable him to make his obfervations with 
perfonal convenience and eafe. In the ins 
fide of the pipe was a jlotteur, or a {pecies 
of pilton, very light, furmounted with a 
long thin light ftalk, made of wood, or of 
a piece of metal that proceeded fromthe 
pipe, and marked by its divifions the 
height of the tide above a certain fixed 
term. It is evident thatthe pipe might 
likewife be furmounted with a vertical 
plate, or piece of metal, whitened and 
properly divided, and fo ‘to mark the 
height of the tides on this plate, by the 
extremity of the ftock 5 or a crayon might 
be adapted to the extremity, which would 
trace the a!cenfion of the water upon the 
metal, and would furnifh the means 
wherewith to afcertain the height of the 
tide, in the abfence of the obfervator, 
However, your commiifioners abandon 
thefe details to the indultry of the obfer- 
vators ; as the only eflential condition is 
accuracy; nothing elfe 1s difficult. 
It would be debrable that metrical feales 
for afcertaining the tides, fhould be eftab- 
lifted in all the ports; they would, be- 
fides, be ufefu] for other objects of mari- 
time fervice ; but as we are not to expect 
that this can be executed wherever it may 
be neceflary, or, at leaft, with all the 
wifhed-for promptitude, your commiffion- _ 
cis 
