——_——_-— ”~ 
—_— 
Méchain, 
Biot, and 
Arago. 
(167.) 
English 
Are. 
Cuap. III., § 1.] 
were the principal means of extricating him from his 
difficulties : but his danger was often imminent, and 
he appears to havesometimes heard the dreadful words 
which, as an eloquent author has expressed it, were 
the last sounds that vibrated in the ear of many an 
unhappy victim.” The operations were actually sus- 
pended for a time by a decree of Robespierre and his 
colleagues, who deposed Delambre, along with Laplace, 
Lavoisier, Borda, and others, from the Commission 
of Weights and Measures, as being deficient in “ re- 
publican virtues and their hatred of kings.” They 
were, however, resumed, and Delambre had finished 
his share of the work long before his colleague Mé- 
chain, whose shorter task was conducted amidst a 
people rude and uneducated, indeed, yet far more to 
be trusted than were then those of the north. Mé- 
chain was apparently wayward and impracticable, 
somewhat too aged for so great a work, yet a really 
good astronomer. The want of agreement to within 
3” of two sets of observations for latitude at Barcelona, 
the southern end of the are at that time, led him to 
the suppression of one of them, and he was tormented 
ever after by the consciousness of the evasion, which 
deprived him of the tranquillity necessary to resume 
and complete his work, which was done chiefly by 
Delambre after vexatious delays! The error, which 
may be said to have cost Méchain his life, was pro- 
bably owing to the instrument employed on this sur- 
vey, the repeating circle of Borda, only fourteen 
inches diameter, with a rather weak telescope. The 
opinion generally entertained in Britain is, that the 
repeating circle was quite inadequate to the prodi- 
gious accuracy required of it, especially in the deter- 
mination of latitudes. The errors of mere division 
are often trivial compared to those inherent in other 
parts of an instrument. Of these a deficiency of op- 
tical power, and the want of absolute security of the 
clamps, upon which the entire success of the princi- 
ple of repetition depends, are amongst the most ob- 
vious. The are was finally prolonged from Barcelona 
to Formentera by Biot and Arago in 1806. The 
conclusion of the survey was not destitute of the ad- 
venturous character of its commencement. The 
French astronomers ran many risks, underwent much 
suffering, and Arago narrowly escaped finishing his 
days in the dungeons of Spain. 
The English survey carried on by Roy and Mudge 
has been also noticed in the previous Dissertation, 
The are from Dunnose to Burleigh Moor amounts 
to 3° 57131, the measured length to 1442953 
feet. An are of parallel was also measured from 
Dover to Falmouth. We shall say something of its 
later progress in the concluding part of this essay, 
but we have still to regret the postponed publication 
of the British Arc of the Meridian, which we have 
no reason to doubt will bear a favourable compari- 
son with the work of Delambre. The practical 
ASTRONOMY —MASKELYNE—DELAMBRE. 
837 
appliances, the three-feet theodolite of Ramsden for 
horizontal angles, and the eight-feet zenith sector 
of the same artist for latitudes, were unequalled in- 
struments, and contrasted in almost every respect 
with the light and portable apparatus of the French. 
By means of the former the spherical excess of terres- 
trial triangles was first observed as a fact, The 
results of the French and British arcs taken sepa- 
rately concurred in showing a local curvature in this 
part of the world altogether anomalous, the de- 
grees rather shortening in the northern part of each 
are. This fact, which must be imputed either to 
large local attractions, giving errors of several seconds 
in the determination of latitudes, or (less probably) 
to a local departure in our quarter of the world from 
the general or mean figure of the earth, sufficiently 
shows the futility of the proposed method of deter- 
mining a natural, recoverable standard of length. 
When combined with the measures of Bouguer in 
South America and Lambton in India, and the revised 
are (measured in the beginning of this century) of 
Svanberg and Melanderhjelm in Lapland, the French 
and English measures give a general ellipticity some- 
what under 344, which is probably as near the truth 
as local inequalities admit of the determination being 
made. 
To Delambre was confided the drawing up of the 
trigonometric formulx used in the calculations of the 
survey, which were published in a separate work ; 
De Prony conducting the laborious calculation of an 
altogether new set of logarithmic tables, with the 
aid of an immense staff of computers, the results of 
whose labour (still in MS.) are preserved at Paris in 
17 folio volumes. Delambre carried his personal 
exertions so far as to compute his own triangles— 
which were also independently calculated by Le- 
gendre, Van Swinden, and Tralles. 
As an acknowledgment of his merit, the highest 
indeed in their power to bestow, the Institute of 
France decreed to him in 1810 one of the Decennial 
Prizes instituted by Napoleon. But the Emperor, 
though professing to be the warm encourager of 
science, suffered some meaner motive to interfere, 
and refused to ratify the decision. “ Ce fut,” writes 
Dupin, “un pas dans la route qui le menait a sa 
chiite.” After the siege of Paris in 1814 Delambre 
wrote a characteristic letter to his friend Moll. The 
tranquil spirit which had braved the horrors of the Re- 
volution was not to be moved by the sounds of the 
artillery of the allied armies. In spite of the can- 
nonade which he heard from his library, he laboured 
from eight in the morning until midnight; and, con- 
scious of rectitude, he feared little the revolution of 
circumstances, which changing dynasties might call 
forth. ‘lLabour,” he says, “occupies all my time 
and all my faculties.” 
As Secretary to the Academy of Sciences for the 
1 The history is minutely given by Delambre himself in his Biography of Méchain.—Astron. du XVIII. Siecle. 
(168.) 
French 
trigono- 
metric for- 
mule and 
tables. 
(169.) 
Prize 
awarded to 
Delambre. 
(170.) 
