THE FIGURE OF THE EARTH. 23 



the western shores of Africa, from Sierra Leone to the Is- 

 land of St. Thomas, near the Equator, then by Ascension to 

 South America, from Bahia to the mouth of the Orinoco, on 

 his way to the West Indies and the New England States, 

 after which he penetrated into the Arctic regions as far as 

 Spitzbergen, and a hitherto unexplored and ice-bound portion 

 of East Greenland (74 32'). This brilliant and ably con- 

 ducted expedition had the advantage of being mainly 

 directed to one sole object of investigation, and of embracing 

 points which are separated from one another by 93 of 

 latitude. 



The field of observation in the French expedition for the 

 measurements of degrees was more remote from the equinoc- 

 tial and arctic zones ; but it had the great advantage of 

 presenting a linear series of points of observation, and of 

 affording direct means of comparison with the partial curvature 

 of the arcs obtained by geodetico-astronomical observations. 

 Biot, in 1824, carried the line of pendulum measurements 

 from Formentera (38 39' 56") where he had already made 

 observations conjointly with Arago and Chaix, as far as 

 Unst, the most northerly of the Shetland Islands (60 45' 

 25"), and with Mathieu he extended it to the parallels 

 of Bordeaux, Figeac, and Padua, as far as Fiume. 19 These 

 pendulum results, when compared with those of Sabine, 

 certainly give -%^-Q for the compression of the whole northern 

 quadrant, but when separated into two halves, they yield 

 a still more varying result, giving T ^-^ from the equator to 

 45, and -^^ from 45 to the pole. 20 It has been shown 



19 Biot and Arago, Recueild'Observ. Geodesiques et Astronomiques, 1821, 

 pp. 526540, and Biot, Traite d'Astr. Physique, t. ii, 1844, pp. 465 

 473. 



20 Op. cit. p. 488. Sabine (Super, for determining the variation in the 

 length of the Pendulum, vibrating Seconds, 1825, p. 352) finds ^irW from 

 all the thirteen stations of his pendulum expedition, notwithstanding 

 their great distances from one another in the northern hemisphere ; 

 and from these, increased by all the pendulum stations of the British 

 survey and of the French geodetic measurement from Formentera to 

 Dunkirk, comprising therefore in all a comparison of twenty -five points of 

 observation he again found TffW- ^ * 8 st ^l more striking, as was already 

 observed by Admiral Llitke, that far to the west of the Atlantic region 

 in the meridians of Petropawlowski and New Archangel, the pendulum 

 lengths yield a much greater ellipticity, namely ^ T . As the previously 

 applied theory of the influence of the air surrounding the pendulum 



