Indian Meridional Arc. 
339 
1831.] 
from the laws of gravitation, that the rotatory motion of the earth must cause an 
enlargement of its equatorial diameter, and a consequent flattening at the poles. 
The most simple and effectual means of verifying this hypothesis was by measur- 
ing arcs of the meridian in different latitudes, and the French academy boasts the 
honour of having set the example, and put in execution the most difficult and deci 
sive parts of this undertaking. 
In less than half a century were accomplished no less than eight new measure 
ments. 
In 1718, 
In 1738, 
berg.) 
In 1745, 
In 1750, 
In 1755, 
In 1760, 
the Dunkirk arc, by Cassini and Lahire. 
the Lapland arc, by Maupertius, &c. (re-examined carefully by Svan- 
the Peruvian arc, by Bouguer and dela Condamine. 
the Cape of Good Hope arc, by La Caille. 
the Roman arc, by Boscovich. 
the Piedmontese arc, by Beccaria. 
»» the Austrian, by Liesganig. 
» the Philadelphian, by Mason and Dixon. 
Phese operations, combined with experiments on the length of the pendulum, left 
no doubt that the earth was in fact flattened at the poles, but the results were not 
sufficiently accurate for determining with precision the degree of compression, or 
cven the absolute dimensions of the globe. It was at the memorable epoch of 
general innovation in France, when a new system of weights and measures was pro 
posed by Cassini, depending on the length of the terrestrial quadrant as an unit, that 
a simultaneous impulse once more actuated the learned world to complete the 
investigation of the earth’s figure, aided by new instruments, new methods, and new 
formul® of calculation. 
In 1 791), Mechain and Delambre were entrusted with the extension of the Ficnch 
arc southward to Barcelona and the Baleares Isles, (which was completed by Biot 
,l,| d Arago in 1806,) while on the north it was united to the English trian^ii , 
f'ui in progress under General Roy, who had brought himself into not 
‘ ociui measurement of abase on Hounslow Heath, in 1784. Upon his ’ 
,JI> ,liis important portion of the task devolved upon Colonel MudgCj w 10 ) 
carried a meridian line from Dunnose to Clifton, and has sinct extim 
northern extremity of the Orkney Isles, whither M. Biot, who had d’stmgu.shed 
i m self at the southern extremity, was deputed by the French Acadcim i 
ai(1 Captain Kater.of the Royal Society, in conducting the final expenmen s ui 
b ndulum, and fixing as it were, the key-stone to this splendid monumtn 
& nd science. 
We have thus in a few words pursued the historical course of geodrtica opera 
|“ S in ‘he west, having purposely reserved for 
. ?0n °nietrical survey, which from our nearer connection wi » hasbecn 
' ,lst sca I e and intrinsic merit (bearing in fact a competition mt review. 
* ' cted in Europe), is, on our part at least, entitled to a more enff 1 in G f 
„ a f ormer part of this work, (vol. 2. page 76,) we have *-cnW 
Ind,f »n survey ; we shall therefore, make as short a recapi 
nt " xtdx the thread of ojur history. 
\ into Irdnndj under 
Sln ce this period, the English triangulation has been earn ^ bce(1 un it c d by a 
° une * Colby’s charge. The French and Italian arcs a tr jg. on ometric d 
1 r P e »dicular arc on the route t>f Mont Cenis, and no the detail* at which 
operations have proceeded in other European countries m 
- as yet unacquaiuted. 
