Sept. 11, 1873] 
NATURE ~ Bt 387 
For the practical purpose of ascertaining the length of 
the meridian quadrant, they proposed to measure an arc 
of the meridian from Dunkirk to Barcelona, a distance’ of 
nearly 9}°, and comprehending about 6° to the north and 
33° to the south of the mean parallel of latitude. These 
extreme points had also the advantage of being both at 
the sea level. The actual operations required were stated 
‘to be as follows :— 
I. To determine the difference of latitude between 
Dunkirk and Barcelona. 
2. To re-measure the ancient bases which had served 
for the measurement of a degree at the latitude of Paris, 
and for making the map of France. 
3. To verify by new observations the series of triangles 
employed for measuring the meridian, and to prolong 
them as far as Barcelona. ; : 
4. To make observations in lat. 45° for determining the 
number of vibrations in a day, and in a vacuum at the 
sea level, of asimple pendulum equal in length when at the 
temperature of melting ice, to the ten-millionth part of 
the meridian quadrant, with a view to the possibility of 
restoring the length of the new standard unit, at any future 
time, by pendulum observations. 
5. To verify carefully and by new experiments the 
weight in a vacuum of a given volume of distilled water, 
at the temperature of melting ice. 
6. To draw up tables of existing measures of length, 
surface, and capacity, and of the different weights in use, 
in order to ascertain their equivalents in the measures 
and weights of the new system, as soon as they should be 
determined. 
In pursuance of the recommendations of this Report, 
the law of March 26, 1791, was passed by the National 
Assembly for constructing the new system upon the pro- 
posed basis ; and the Academy of Sciences was charged 
with the direction of the necessary operations. They 
entrusted the measurement of the arc of the meridian 
from Dunkirk to Barcelona to two of their members, 
Méchain and Delambre, who carried on the work during 
seven years, from 1791 to 1798, notwithstanding many 
great difficulties and dangers. 
The unit of measure adopted for the actual measure- 
ment was the existing French standard of length, the 
Toise of the Academy, better known as the Zozse de Perou, 
a measure of 6 French feet (Pzeds du Roz). This standard 
- is now deposited at the Observatoire at Paris. Itis a bar 
of polished iron, about 14 inch in breadth, and 4 inch in 
thickness, and a little longer than a toise. The length of 
a toise is marked by a rectangular step near each end of 
the bar, leaving the remaining portion at the ends half 
the thickness of the measuring part of the bar. 
The true length of the toise was taken about a line 
(or 74; inch) above the re-entering angles of the bar, 
at the temperature of 13° Réaumur, or 16°25 C. It has 
been declared to be equal to 76'7563 English inches, the 
old French foot (which was divided into 12 inches and 
the inch into 12 lines), being equal to 12°792 English 
inches. The toise was afterwards found to be equal to 
1°94904 metre, 
This standard had been originally constructed as the 
unit for measuring an arc of the meridian in Peru, and 
for verifying the meridian of Paris, in 1740; and it was 
substituted in 1766 for the more ancient French standard 
of length, the Zozse du Grand Chatelet, from which it had 
been originally derived. This older toise was deemed 
wanting in the scientific precision requisite fora standard 
ef length. It had been constructed in 1668, and is said 
to have been 5 lines shorter than the toise measure then 
ordinarily used, for which no authoritative standard could 
be found; and to have been actually derived from the 
width of the inner gate of the entrance to the Louvre, 
which, according to the original plan, was made 12 feet 
wide, and one half of this width was taken for the length 
of the standard toise. 
The measures actually used for the survey operations 
are known as the Rég/es de Borda, They were four in num- 
ber, each consisting of a bar of platinum two toises, or 
12 French feet, in length, about 4 inch broad, and 7 inch 
thick. Each platinum bar was fixed at one end only toa 
bar of brass about 113 feet long, the other end of the 
platinum bar being free and extending about 6 inches 
beyond the corresponding end of the brass bar. The 
object of this second bar was that it should form, to- 
gether with the first bar, a metallic thermometer, indi- 
cating the temperature of the two bars by their difference 
of dilatation, which could be measured by a fine vernier. 
The four measuring bars were accurately verified, and 
found, when placed together, end to end, not sensibly to 
differ from eight times the length of the Toise of Peru at 
the temperature of 12°5 C, 
The base for the measurement of the northern portion 
of the work was measured at Melun, and found to be 
6075"90 toises. The base for the southern portion was 
measured at Perpignan, and found to be 600625 toises. 
Meanwhile the Academy of Sciences was abolished in 
1793, by a decree of the National Convention, and a 
Commission of eleven scientific men, consisting prin- 
cipally of those who had been previously engaged in the 
proceedings, was appointed, in 1795, to carry out all‘the 
arrangements for the definitive establishment of the Me- 
tric System. In 1798, towards the close of the opera- 
tions, an equal number of scientific men, representatives 
of foreign countries, .were added to the Commission, 
which was then composed as follows :— 
French Members: MM. Borda, Brisson, Coulomb, 
Darcet, Delambre, Lagrange, Laplace, Lefevre- 
Gineau, Legendre, Méchain, de Prony. 
From the Batavian Republic: Aeneae, Van Swinden. 
Sardinia: Balbo, afterwards replaced by Vassali, from 
the Provisional Government of Piedmont. 
Denmark: Bugge. 
Spain: Pédrayés, Ciscar. 
Tuscany : Fabbroni. 
Roman Republic: Franchini. 
Cisalpine Republic : Mascheroni. 
Ligurian Republic; Multedo. 
Helvetian Republic: Trallés. 
The final results of all the operations for determining 
the new metric unit of length, were stated by the Com- 
mission in their Report, dated April 30, 1799. They 
found :— 
1. That the length of the arc of the meridian compre- 
hended between Dunkirk and Barcelona, was 9°6738° 
(or 9° 40’ 45”), and measured 551,584'72 toises. 4 
2. Assuming, from the previous measurements in 
France and Peru, that the mean ellipticity of the earth 
was 5} , they computed the length of the meridian- 
quadrant to be 5,130,740 toises, : 
3. That the length of the new unit of length, the ten- 
millionth part of the meridian-quadrant, was equal to 
0°5130740740 toise, or 3 feet and 11'296 lines; being 
443'296 lines of the Toise of Peru (which contained 864 
lines), at its standard temperature of 16°25 C. In terms 
of the new standard unit, the Toise of Peru was equal to 
1°949036591 metre. 
4. That the length of the pendulum at the temperature 
of melting ice, beating seconds in a vacuum at the sea 
level at Paris, was equal to 0'99385 metre. 
The actual construction of the new standard measure - 
of length had been entrusted to the mechanician Lenoir. 
As a preliminary proceeding, he made four end-standard 
metres of brass, differing in length very slightly from 
each other, and each about equal to 443'242 lines of the 
Toise of Peru. This was the computed length of one 
ten-millionth part of the meridian-quadrant, as deduced 
from the previous measurements of an arc of the meridian 
in France made in 1740. The length of these four brass 
metres, when placed end to end, was nearly 1,773 lines, 
