412 Mr. Ivory 07i the Figure of the Earth. 



Substituting the above values of u and ^ in the expressions 

 for a and J", we find : 



The three-hundred-and-sixtieth part of the terrestrial me- 

 ridian = 0*57008*655 toises; the ellipticity = ■. 



The mean error to which the value ofyis subject, is = 4i'26 

 toises ; and the mean error to which the value of a is subject, 

 is = 10"5 unities of the denominator. We have next, 



a = 3271852-32 toises; b = 3260853-70 toises. 

 With regard to the formulae applied in these calculations, 

 I refer to the first volume of my " Mathematical and Physical 

 Geography," the printing of which is nearly finished. 



Edward Schmidt. 



LVIII. Ofi the Figure of the Earth. By James Ivory, Esq. 



M.A. F.R.S. <§r.* 

 'T^HE 8th volume of the Memoires de VAcademie des Sciences, 

 ■*■ published in 1829, contains a paper on the figure of the 

 earth by M. Biot, who has had so great a share in the ex- 

 perimental researches relating to that subject. Accompanied 

 with his son and assisted by him, M. Biot determined in 

 1824 the lengths of the pendulum at Milan, Padua, and 

 Fiume, upon the parallel of 45° ; and as the same parallel 

 passes through the old stations of Bourdeaux, Figeac, and 

 Clermont, we are thus made acquainted with the lengths of 

 the pendulum at the six principal stations of the great arc 

 perpendicular to the meridian, extending fiom Bourdeaux to 

 Fiume, which has lately been measured geodetically with so 

 much ability and exactness. We are indebted to the same 

 observers for the pendulums at the two new stations of Lipari 

 and Barcelona ; and for a remeasurement of the pendulum at 

 Formentera, the old length in the 4th volume of the Base 

 Metriqtce being for some reasons deemed exceptionable. Ac- 

 cording to the new measurement, the pendulum at Formentera, 

 in a vacuum and reduced to the level of the sea, is 993™'" -0697; 

 the length as stated in the Base Metrique is equivalent to 

 992"'"'-9761 ; the difference Qi^^-OdSS is very considerable, and 

 answers to about four vibrations in a day. 



The most curious part of M. Biot's paper is an attempt to 

 prove that the lengths of the pendulum in different latitudes 

 are not accurately represented by the foimula usually em- 

 ployed : for he finds that the coefficient of the term propor- 

 tional to the square of the sine of the latitude, is not an invari- 



• Coinniuhicatod by the Author. 



able 



