316 FIGURE OF THE EARTH. 



Between Villojuif and Juvisi, Picarcl measured a base of 5.663 toises, and 

 by mcaud of five triangles, resting on that line, deduced a distance from Mareil 

 to Malvoisin equal, in the units just cited, to '32S97. This line, much greater 

 than the lirst, served him now for a base to connect Malvoisin with Sour- 

 don, near Amiens, by a chain of triangles in the direction of the meridian. 

 The arc comprised between the two last points was 1° 11' 57", and the dis- 

 tance deduced from the triangulation and projected on the meridian was 68.4.30 

 toises ; whence there resulted for the value of a terrestrial degree the number 

 57064. Still later, Picard extended the operations to Amiens, and the degree 

 then stood reduced to 57.057 toises ; or, taking a middle term, to 57.060 ; 

 a result which, assuming the sphericity of the globe, implied as the length of 

 the earth's radius 3,269,300 units of the above name.* 



Although in this memorable operation, on which we have dwelt somewhat, 

 as being the first among those really worthy of confidence, Picard displayed 

 great talent and activity, the result obtflincd was closely approximate to the 

 truth only through a singular combination of errors ; since, as appeared in the 

 sequel, there was a very considerable one in the value of the first base, nor 

 was that which existed in the quantity of the arc insignificant; two circum- 

 stances which, as they affected the result in opposite directions, were neutral- 

 ized as regarded the operation itself, but were afterwards the source of much 

 extraneous confusion and of long and warm discussions : a sad proof that im- 

 perfection, under some disguise or other, lurks in all the works of man ; and 

 that, without doing injustice to the memory or merits of the learned, wc should 

 never blindly surrender our belief to their authority. 



The rotation of the earth being by this time a fact received without contra- 

 diction in the scientific world, of necessity soon drew with it its natural conse- 

 quences : thus, the ideas of the less weight of bodies at the equator than in 

 the neighborhood of the poles from the eff'ect of the centrifugal force opposed 

 to gravitation, and of the compression of the globe in the direction of the axis 

 of movement, had begun to take root in all refiecting and unprejudiced minds, 

 when an observation, in some degree unexpected, gave confirmation to this 

 view of the question. The academician Richer, having been sent to Gruiana, 

 in 1672, for scientific purposes of different kinds, returned to his country the 

 following year, and among other results of his expedition presented to the 

 Academy an observation which, though incidentally made, proved to be the most 

 important of all : the astronomical pendulum which, at Paris, gave an oscilla- 

 tion of one second, was found to move more slowly in Guiana, to the extent 

 of making in a day 88 oscillations fewer than at the former point. This indi- 

 cated an energy of gravitation at the equator inferior to that in high northern 

 latitudes, the existence of the centrifugal force due to the rotary movement of 



* Tlie toise spoken of is that of Franco, containing 0.39459 feet, which dates from the time 

 of Chaiiemague, ami is said to have originated with the Arabs. For many centuries the 

 standard of this unit of measure was little known, and from time to time underwent modifi- 

 cations, tiie results of ignorance or carelessness more than of fraud, until in lOGrf a new one 

 was prepared and deposited in a secure place, in order to serve as a type for all of its kind ; 

 it was to this standard that Picard and the geometers who succeeded him referred their geo- 

 desic operations. A century afterwards the iron rule which was adopted for the standard of 

 measmement of trigonometrical bases in Peru, also a toise in length, but better constructed 

 than the toise of Picard's time and in a better state of preservation than the latter, was, at 

 the suggestion of Condamiue, declared to be the legal miit, at a temperature of l'.P Reaumur, 

 or 1(5" centigrade, that having been its medium temperature during the operations near 

 the equator. The subsecpieut labors of Delambro and JMechain served to fix the length of 

 the new lineal unit, or, in other words, of the metre, which, at tho temperature of 0" is, in 

 lines, 44;?, 290, thus establishing between the metre and the toise the ratio of 1 to 1.94901)031. 

 This last number has been employed as factor in the remainder of this article, while it has 

 been thought proper to convert tho ancient units into the modern, or more usual of tho deci- 

 mal metric system. 



