On the Figure of the Earth. 295 
was of a round figure, and that was easily ascertained by the cir- 
eular form which its shadow presents when projected on the 
moon’s dise during an eclipse. Newton discovered afterwards by 
his calculations, that it was not completely round, but was some- 
what flattened at the poles and distended at the equator. The 
methods of observation, yet imperfect, after great difficulty, 
have established this truth. It has been at last obtained by mea- 
suring the terrestrial degrees under the most distant latitudes, 
namely, at the equator and at the poles. The flatness of the poles 
was thus put beyond doubt. ‘The operations undertaken for the 
last fifty years in France, England, Sweden, America, and India, 
have succeeded in determining its precise quantity. It has been 
imagined, therefore, that a great idea conceived a long time - 
since, might be realized upon these results,—that of forming a 
system of national measures adapted for universal use, which 
might have for its base the extent of the earth itself. The mea- 
surement of the are of the meridian comprehended between Dun- 
kirk and Barcelona, and accomplished with infinite precision by 
Messrs. Mechain and Delambre, was the principle of all these 
conclusions: better could not be selected. The desire of com- 
municating to these results, not greater precision, for it would 
have been difficult to hope for it, but a new assurance, and a base 
not so peculiar to France, has caused this first are to be pro- 
longed across Spain as far as the Pithiuse Isles. Contingently, it 
became a part of an immense triangle above the Mediterranean. 
In fine, the same motive has still caused to be seized with ex- 
treme anxiety the opportunity which was offered, two years ago, 
of seeing this operation, already so grand, extend itself towards 
the north, to nearly equal extent, in uniting with a portion of the 
same meridian which stretches from the southern coasts of En- 
gland as far as the Shetland Isles toa higher latitude than St. Pe- 
tersburgh—a portion which the learned men of England have 
been now twenty years occupied in measuring. In order to ter- 
minate this immense are, which comprehends almost the fourth 
of the distance from the equator to the pole, and which unites to 
this extension all the exactitude of mental observation, there re- 
mained nothing, last year, but to erect some triangles between 
the Shetland Isles and Scotland, by the medium of the Orkneys, 
and to connect the operations of the English and the French at 
the point of junction, consequently at Dunkirk, by means of a 
system of combined operations in which instruments of a very 
different nature, employed by the observers of the two nations, 
would be made to co-operate. This last labour was executed in 
the preceding autumn. M. Arago and I went to receive, at 
Dunkirk, the English observers, MM. Mudge, Coleby, and Gard- 
ner, They brougnt with them the grand astronomical sector con- 
T4 structed 
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