1 8(5 rrench l^iit'ional Injl'ituie. 



lias not hccn deceived. Laplace, in confequen'ce tff M* 

 Burg's defile, has exaniined the qucllion, and found that! 

 there exifts in the liniar orbit a motion of nutation analo- 

 gous to that of the tcrrcftrial equator. The extent of this 

 nutation depends ou the oblate form cf the earth, and may 

 throw new light on that important element, fince the in- 

 equafify thence refulting varies fron> one' id two, according 

 as the fla£ne{s \i fuppofecl to Fje j-j-^^ or ^^c- 



Another equation, depending on the fame theory, aflefts 

 the iTirtorr's longitude, and is of eqtlal importance in enabling 

 us to afcertain the quantity of the earth's fTatnefs. As long 

 as the real caufe was unknown, great uncertainty prevailed 

 in regard to the ufe which ought to be made of this equa- 

 tion, and allronomers omitted it in their calculations. Th(? 

 exillence of it was proved by obfcrvations, but it was indi- 

 cated l)v no theory. Laplace himfclf, having calculated by 

 the principle of univerfal gravitv, carried it only to 2", that is- 

 to fay, to a third of its real value. But fi.trce he has lakcir 

 into account the nutation of the lunar orbit, he has found that 

 it indicates the flatnefs to be nearly what it is known to be 

 from other j)henomena. 



To afcerfain it dill better, he made C. Bouvard fele6l from- 

 his paper which gained the prize three months ago, thofe 

 obfcrN'ations belt fitted for deciding the queltion propofed 

 by M.'Biirir. This refearch was attended with con)plete 

 fuc'cefs, and 440 deeifive obfcrvations have given 7" 5 as the 

 co-efficient of the new equation of latitude, which fuppofea 

 a flatnefs of j' t . This is nearly what has been given by the 

 variations in the length of the pendukim as obferved in dif- 

 ferent latitudes. The meafurement of degrees in France and 

 Peru give Itill fomewhal Icfs, and therefore it is demonilrated 

 that the flatnefs -^^i^, as found by Xewton, fuppofing the 

 earth homogeneous, is by far too much. The uncertainty 

 which may yet remain refpefting a quantity the caufe of fo 

 much difpute, will in future be confined within very narrow 

 limits : three phenomena, of a very different kind, lead us 

 to the fame conclufion. 



Thus the moon, which, by her eclipfes, made known to 

 the ancient allronomers that the figure of the earth is fenfibly 



round. 



