1708. ] Proceedings of the National Inftitute, 15 Nivofe, 1798. 26g. 
lation.of magnitude with the quarter of. 
the former, indicates the heights of the 
water above a low bottom, fituated oppo- 
fite Chaillot, which is at the egreis of 
Paris, a place of the river where> the 
4epth is the leaft, and where the naviga- 
tion is the moft impeded. A comparifon 
between the obfervations made by thefe 
two fcales gives the daily variation of the 
fall of the water in pafling through Pa- 
ris, which is extremely irregular: in 
order to deduce from thefe obfervations 
the abfolute quantum of the fall, the dif- 
ference of level between the zeros of the 
-wo fcales muft be calculated ; Citizen 
Prony has found by a level made with 
great caré, and frequently repeated, that 
this difference was 5 feet z inch, or 
metre 650 centimetres. 
Citizen BEAUCHAMP, ‘an aflociate 
member, and coni{ul of the republic at 
Mafcata, has tranfmitted tothe clafs fome 
details on the aftronomical and geogva- 
phical operations he was defired to per- 
form on the part of government ; his let- 
ter on the 25th Vendemaire lait, an- 
ounces his having fent to the minifter of 
marine a chart of the fouthern tract of 
the Black Sea, accompanied with a nau- 
tical memoir on the fubje@ ; another me- 
moir addrefied to the minifter of exterior 
relations, furnifhes details on the hiftori- 
cal part of his voyage; he has left to the 
embafly the original manuicript of his 
obfervations, the forwarding of which to 
Paris for the perufal of the aftronomical 
and geographical literati, would be a de- 
_ firable obje&t. The laft letter of citizen 
Beauchamp announces his intention to 
fail from Conftantinople to Alexandretta, 
and it is from thence probably that he 
will fet out on his great Arabian and 
Periian voyage, the defign of which he 
has long entertained. 
We announced in our laft public fit- 
ting; that the aftronomers DELAMBRE 
and MECHAIN appointed to mealure the 
arch of the meridian included between 
the parallels of Dunkirk and Barcelona,, 
iad completed a part of their work relat- 
ing to the aftronomical obfervations and 
to the angles of the triangles, and that 
there only remained two bafes for them to 
meafure. This laft operation is that 
which muft give the abfolute length of all 
the fides of the triangles formed in the 
direction of the meridian, the preceding 
operations only ferving to determine the 
relations of thofe fides, or to form a figure 
fimilar to that which refults from their 
affemblage ; there will be thus two lines 
meafured immediately on the French ter- 
gitory, from which will be found the re- 
MONTHLY Mac. No. XXXVII, 
\ 
the terreftrial meridian, and which will 
be the medium of comparifon between 
that meridian and the fundamehtal unity 
of the new fyftem of weights and mea- 
fures. This unity has been conditionally 
determined by the Academy of Sciences 
and the commiffion of weigits and mea-. 
fares, agreeably to the operations made in 
France from 1739 to 1744, old ftyles 
and the public will learn with fatisfaction, 
(aat it appears from many accurate verie ° 
fications made by Delambre and Mechain 
in the courfe of their labours, with mc- 
thods amd inftruments much fuperior to 
thofe employed 55 years ago, that the. - 
precifion obtained by Caflini and his col- 
laborators, is as great as could be expeét- 
“ed and defired at the time of their la- 
Yours ; the greateft errors do not exceed 
the limits of + and of ——, and we may 
feaja)} 1004090 
confider the provifory fixation of the me- 
tre, as bearing an exaétnefs more than 
what is neceffary for the ordinary opera- 
tions of trade and almof all the arts. 
The commitlion of weights and mea- 
fares could have wifhed that the ba to 
be meafured near Paris, might have been 
on the {cite of that of Villejuif, fo cele- 
brated by the. frequent meaiurements 
which the French academicians had made 
there; but the alterations’ produced in ‘ 
the furface of the grounds by the hands 
of men in the courte of 60 years, raifed 
infurmountable obftacles to this project. 
They were forced therefore to chufe 
another place, and after mature exami- 
nation, it was agreed to fix upon for the 
bafe @ part of the paved cauieway between 
Licurfaint and Melun, the length of 
which is about 1200 metres. 
The inftruments to be made ufe of 
for the meafure of this bale, are of 2 
conftruction altogether new, and more 
proper ,than any of thofe made ufe of be- 
fore, to preclude errors of every kind: 
one of their principal.advantages over the 
former inftruments, confitts in the method ~° 
of keeping account of the variations of 
length which the diiterent teinperatures 
of air caufe the metal rods to undergo; 
to obtain this correction they have made 
ute of the different degrees of dilatability 
of platina and of copper by heat. Kach 
of the meaiures which are placed end to 
end, coniifts of two rules, one of platina, 
and the other of copper, fixed \together at - 
their Jower extremity, and beariug at 
their interior extremity, divifions, the dif- 
ferent co-incidences of which produce the 
elongations or contra¢tions which are to 
be eftimated. This method is in all re- 
z M fpects 
