GEOGRAPHICAL LATITUDE. 789 



ainous nature of the regiou favored large triangles, generally of a form 

 advantageous to the ease and accuracy of observation. The frozen 

 surface of the river Tornea offered an excellent opportunity to measure 

 a base line ; so good in fact that Maupertuis neglected to take any ac- 

 count of its fall. This action has been censured by later mathemati- 

 cians, who have consequently corrected his result by 5.355 toises.^ 

 His base line was 7,406.86 toises long, the two measurements differing 

 only 4 inches'^ from each other. Calculating from this basis, he found 

 his meridian line to be 55,023^ toises long, which, compared with the 

 amplitude,^ gives the length of a degree of latitude crossing the Polar 

 circle 57,438 toises.'' Comparing this result with Picard's measuie- 

 ment and leaving out of the reckoning the aberration of light, which 

 was unknown to the latter, Maupertuis's arc would have an amplitude of 

 57' 25," and this, compared with the length, would raise the value of a 

 degree at the polar circle to 57,497 toises or 437 toises greater than Pi- 

 card's result in France; and, taking the aberration into account, Mau- 

 pertuis's result differs 950 toises from that which it ought to be, follow- 

 ing Cassini's calculations based on the supposition of the earth being 

 elongated at the poles.^ 



The expedition to Peru met with a series of difficulties, which, com- 

 bined with party strife and the length of the line surveyed, detained the 

 experts nine years ; so that the principal question, which caused their 

 going, viz, as to the form of the earth, was already settled forever before 

 their return, and the results achieved only served to add another factor 

 toward arriving at exactness in the solution of the matter. A couple of 

 Spanish representatives also took part in the operations. The company 

 was provided with several quadrants, on one of which was the first 

 micrometer ever so applied.^ Their astronomical observations were 

 made with a sector of 12-foot radius, and their base line was measured 

 with wooden rules 20 feet long. On the ends of these were fastened 

 projecting copper plates, so arranged that, in measuring, those of neigh- 

 boring rules stood at right angles to each other. In measuring, three 

 rules were laid on the ground in a straight line, level being secured by 

 means of wedges. The line was maintained by means of a stretched 

 cord, and the surveyors had to lie on the ground ^^pour les disposer''''.'' 

 They knew that these rules were subject to variations according to 

 changes in the humidity and temperature of the atmosphere, and found 

 themselves "obliged to examine each day and often several times the 

 little equation or correction that was necessary to apply to them."^ For 



' Zach, Mod. Cor., Januar, 1806, p. 20. 

 * Maupertuis, CEuvres, iv, 301. 



^ Ibid., m, 152, adopts amplitude of 57' 27," that giveu by obaervatiou of only one 

 star. 

 *md., IV, 331. 

 ^Ihid., Ill, 167, 16S. 

 " Boiiguer, Figure de la terre, 60, 61. 

 "I Ibid., p. 40. 

 ''Ibid., 40,41. 



