138 
-ers are of opinion that thefe eftablifhments 
are abfolutely neceflary in the principal 
ports, fuch as at Breft, at L’Orient, at 
St. Maloes, at Cherburg, at Havre, at 
Dunkirk and at Flufhing. They obdferve, 
moreover, that there are many places where 
the obfervations here alluded to, might be 
eafily made and without any expence, 
namely thofe where the ftate maintains 
keepers or guardians of jetties, fires, fig- 
nal-houfes, &c. for the fecurity of naviga- 
tion, as at Boucaud, at Cordouan, at the 
towers of Chaffiron, and La Baleine, at 
Le Pilier, on divers peimts of the coalts of 
Brittany, at Granville, at Cherbourg, at 
Dieppe, &e. Thofe guardians might 
eafily be trained to perform the moft ma- 
terial parts of the ob{ervations, by the pro. 
feffors of navigation, in the ports where 
there are any eltabisfhed, and in the other 
places by other perfons, who would at 
once acquit themfelves of a duty anda 
pleafure. é 
The precife time of high water is an 
effential point to determine ; it becomes 
neceflary, therefore, that the obfervators be 
thoroughly well informed as to the real 
time of the day. In places, as at Breft, 
where there is an oblervatory, this may 
be eafily done; but in the other parts, the 
true time muft be determined by corref- 
ponding heights, taken with an octant, or 
with a jextant, or with a circle of reflec- 
tion by means of an artificial horizon ; and 
gn defect of an artificial horizon, made for 
the purpofe, the obfervato; may make ufe 
of the reflet:ion of water, taking care to 
fecure the veffel’ from the action of the 
wind. 
To afcertain more correctly the exact 
moment of high water, about half an 
hour before the fame, the periods at which 
the fea will anfwer to different divifions of 
the fcale, fhould be noticed, and likewife, 
when the water is falling, the periods 
when it arrives at the fame divifions: 
then the half of the interval of time con- 
tained between the two correfponding ob- 
fervations, will indicate the time of high 
water, agreeably to the above two obfer- 
wations. The fame method being obferved 
for every pair of correfponding obferva- 
gions, and taking a medium or average 
from all the refuits, the time of high water 
may be fettled with ail the precifion that 
ean be defred. 
The exact time of low water, that ts to 
fay, when it difcontinues falling, is, in 
- ke manner, an object of importance to 
determine: to effect this, recourfe fhould 
be had, likewife, to correfponding obfer- 
vations. Of courfe, about half an hour 
Proceedings of Learned Societies. 
[Sept. 1, 
before low water, the obfervator fhould 
note down the time when the water fuc- 
ceflively arrives at different divifions of 
the fcale, and at the return, fhould like-., 
wife mark the time when the water reaches 
the fame divifions ; from whence he may 
fix upon the exact time of low water. 
In places where the conveniences, here 
referred to, cannot be had, it may never- 
thelefs be poffible to make ufeful obferva- 
tions. Jo obtain the trve time, it will! 
be fufficient to trace a meridian, by which 
to regulate a common watch. ‘The fea- 
weeds and the fleeces of foam which the 
fea leaves every tide on the coafts, 
while it is retiring, corre€tly mark the 
place to which it has afcended, and it only 
remains to determine the infant when it 
has arrived at this height. For this pur- 
pofe, about half an hour before high 
water, it would be barely neceflary to 
plant certain piquets on that {pot of the 
‘beach where the flood terminates, and to 
note the time ; and likewife, when the 
water is falling, to obferve by the watch, 
the periods when the tide fucceffively ar- 
rives at the fame marks ; which will fur- 
nifh the means of afcertaining the time of 
high water, with tolerable precifion. The 
fame means may be reforted to, to deter- 
mine the exact time of low water. 
Thefe lat obfervations do not immedi- 
ately furnifh the abfolute height of the 
tides; but having marked on the fhore 
the place to which the fea has rifen, and 
that to which it has fallen, it will be eafy 
to find its total elevation, by taking a 
level; an operation which may even be 
poftponed to another time, when the marks 
are permanentand diitinét. If the ebier- 
vations are made regularly in the fame 
place, fome large flones might be fixed, 
permanently, on the thore, and, once for 
all, their difference might be tranfported 
by the level to an adjacent rock; and 
thus there would be formed, even cn the 
declivity of the fhore, a very exact fcale, 
the parts of which would be very large. 
Tt is an obferved faét that the declivity cf , 
fandy coafts, wafhed by the fea, is pretty 
uniform, and the variations cn different 
fhores are not confiderable. If preference 
be not given to the buildings already con- 
ftiuéted, for the purpole of eftablfhing 
feales of the tides, we fhould incline to 
fuch {cales as follow the declivity of the 
coaft, in preference to vertical {cdles : 
their .confruction would be much lets ex 
penfive, and their ufe more convenient. 
When they follow exaétly the natural in- 
clination of the coaft, the fea there will be - 
very gentle, and the obfervations more ac- 
curate 
