582 
mentioned. To employ, fays the re- 
porter, Van Swinden, as the fundamental 
unity or ftandard of all meafures, a ftand- 
ard taken from nature itfelf—~a ftandard as 
unchangeable as the globe we inhabit; to 
propofe a metrical fyftem, having all its 
parts intimately connected, with its multi- 
ples and fubdivifions following a natural 
progreffion, which is fimple, obvious, and 
always uniform; this is a beautiful, 
grand, and fublime idea, worthy of the 
prefent enlightened ase. ‘This ftandard is 
founded on the bafis of the circuit of the 
earth being the fourth part of the terref- 
trial meridian, contained between the equa- 
tor and. the north pole. The ten millionth 
part of this quadrantal arc was adopted to 
be. the lineal meafuring unit, which the 
called metre, applying it equally to fu- 
perficial and folid meafures, taking for 
the unit of the, former the iquare of the 
decuple ; and for that of the latter the cube 
of the tenth part of the metre. They 
chofe alfo, for the meafuring unit of 
weight, the quantity of diftilled water 
equal .in bulk to the fame cube in a con- 
ftant ttate prefented by nature, viz. of a 
certain temperature. ind Iaftly, it is de- 
cided, that the multiples and {ubmultiples . 
of each kind of meafure, whether of weight, 
capacity, furface, or length, fhall be al- 
ways taken in the decimal or decuple pro- 
greflion, as the moft fimple, natural, and 
ealy for calculation, according to the fyftem 
of numeration which all Europe nas ufed 
for many centuries. 
As the bafis of this new metrical fyftem 
depends on a quarter of the terreftrial me- 
ridjan, it is neceffary that the magnitude 
of this arc fhould be known to great pre- 
cifion. ‘Therefore, although, many diffe- 
rent degrees of the meridian have been 
carefully meafured at feveral times, and in 
different countries, the Inftitute ordered a 
new and aétual meafurement of the whole 
arc of the meridian, extending the whole 
length of France, viz. from Dunkirk, on 
the north, to Barcelona in Spain, and paf- 
fino Paris ; an extent of almott ten degrees. 
Tike meafurement of this arc, in feveral 
years, was at length completed by Me- 
chain and Delambre, two eminent altros 
nomers; in which they employed rules or 
rods made of re “of two toifes or 12 
feet in length, for meafuring the bales ; 
and whole circles, accurately made, for 
taking the angles, to tenths of fecontles by 
vepeating the meafures in many different 
parts of the circumference, and taking 
mediums of the whole. ‘The precifion 
Account of ihe French Metre. 
7 
: 
with which the angles were obferved is 
fuch, that out of go triangles which connect 
the extremities of the meridional arc, there 
are 36 in which the fum of the three an- 
gles differs fromm its proper guantity_by 
lefs than one fecond; that is, in which 
the error of the three "anoles, taken toge- 
ther, is lefs than one fecond: there are 27 
triangles, in. which this error is Jefs than 
two feconds; in 28 others it does not 
amount to three feconds ; and there are 4 
triangles, in which it falls between three 
and four feconds ; and three triangles enly 
in which it is more than four, but Jefs than 
five feconds. 2 
Every care was taken to fapport and 
-difpofe the platina rods properly in mea- 
furing the bafes. The extremities. of the 
rods were never brought into contaét; an 
interval being left, which was meafured 
by a tongue of platina, fliding from the 
end of one of the rules, and carrying a 
vernier and microfcope. The correétions 
or allowances for differences of tempera- 
ture, for obliquities of the line actually 
meafured, and for the elevation above the 
level of the fea, were alfo attended to, and 
allowed. for. One rod was kept uném- 
ployed, for a module or ftandard, which 
was exactly equal to the double toife of 
Peru, in ten degees temperature of Reau- 
mur’s thermometer; or fifty- -four of Fah- 
renheit. With this module, and allo 
with the toife of Peru, the other meafuring 
rods were compared, both before and after 
the operations of meafuring, and found not 
to be at all altered. 
The celeftial latitudes, &c. alfo obferv- 
ed with the fame repeating circle of Borda, 
arefuch as not to have an error of any 
thing near half a fecond. 
The fetthng the article of the meafure 
of weight was ‘deputed to Lefevre Gineau, 
together with Fabroni of Florence; and the 
calculations from the meafures of Mechain 
aid Delambre, and the management of the 
whole bufinefs, were under the a ectionand 
conduct of anumber of commiffioners, feve- 
yal of whomweredeputed fromother nations: 
their names were Mefirs. Atnee, Balbo, 
Borda, Briffon, Bugge, Cifcar, Coulomb, 
Darcet, Delambre, Fabroni,La Grange,La 
Place, Lefevre- Gineau, Legendre, Fran- 
chint, Mafcheroni, Mechain,  Nhulted@s Pe- 
derayes, Prony, Tralles, Van Swinden, and 
Wafiali. And the refult of the whole bu- 
finefs is contained in the following fynopfis 
of the meafures in nels which we 
have here allo reduced to English mea- 
fures. 
The 
[ December, ) 
