( 270 ) 



AN ABRIDGED RELATION 



OF A 



VOYAGE TO PERU, 



Undertaken by Gentlemen of the Royal Academy of Sciences, to meafure the Elegrees of the 

 Meridian near the Equator, -whereby to infer the Figure of the Earth. — By M. Bouguer. 



TRAHSLATED FROM THE FRENCH. 



THE Academy has been fo diligent in publifhing every thing it has done to determine 

 the magnitude and figure of the earth, that I am warranted to fuppofe the affem- 

 bly perfeftly inftrudted with the ftate of the queftion *. The experiments already made 

 to afcertain the weight of bodies which are found to diminifh therein in proportion as 

 they draw towards the equator ; the various operations undertaken in France to meafure 

 the extent of the degrees of both latitude and longitude ; every thing, indeed, concurs 

 to fatisfy us, that the earth is not completely fpherical ; but thefe very experiments and 

 operations are known to lead to oppofite conclufions as to its real deviation from this 

 form. Geometry and phyfics feemed here fo much in contradiction with each other, 

 that none were fufEciently aware of the means of reconciling them ; it was a contro- 

 verfy to which the learned themfelves gave rife, and not one of thefe difputes deemed 

 purely fpeculative, and of no importance in practice : even the academy itfelf were 

 undecided ; nor were its doubts entirely laid at reft until fome voyages had been accom- 

 pliftied to the pole and the equator. The errors to which all our operations are liable, 

 are not to be corrected by comparing, only,, degrees of latitude within a fmall extent ; 

 their inequality is not manifeft enough to be depended on : it is a very different thing to 

 compare the degrees meafured in regions very remote, as is the pole and the equator, 

 from each other. The difference produced from the fum of the whole of the fmall 

 differences of thefe meafured degrees, muft have, neceffarily, by reafon of its magni- 

 tude, difengaged us from thofe errors not to be avoided by calculating the difference of 

 one degree from another feparately ; and the confequences drawn from the mode of the 

 firft calculation, had acquired a certainty the latter could not give. 



If towards the perfecting navigation it had been conceived neceffary to afcertain the 

 magnitude of the degrees of it, it was not of lefs confequence to be acquainted with its 

 exaft figure. They were not able to diftinguifh whether the accidents, which happen 

 even now, too frequently at fea, ought or not to be imputed to the negligence of pilots, 

 not fcrupuloully enough attentive to the precepts of their art, or whether the evil were 

 not to be traced to a higher fource, — to the imperfeCtnefs of the art itfelf, by the maxims 

 of it being chiefly founded upon the fpherical figure of the earth ; of which it ought 

 neceffarily to be aflured, as well as of the circumftance, if fuggefted to it, of the im- 

 perceptible irregularity of the figure. Setting afide every other advantage which may 



* One part of this difcourfe was publiqjy read in the Aflembly of the Royal Academy of Sciences, 

 J 4th November 1744. 



have 



