194 Niw Syjlem of Weights nnd litcafura of France, 



but it prefented two inconveniences : the firft, that the dtvifion of time is in itfcif ar- 

 bitrary*; the fecond, that the nic;ifures thence rcfulting, and geographical meafurcs de- 

 pending on the magnitude of thq earth, would have no mutual agreement f. 



The preference was given to refer all meafurcs large and fmall to the tcrreftrial globe. 

 Among the great circles which nieafure its circumference, the preference was not given to 

 the equator. The nature of the countries over which it pafTes, renders the obfervations too 

 difficult. The determination was made in favour of meridians {. 



The whole meridian was not taken as the unity for fubdlvifion, for two reafons : the firft, 

 becaufe the quadrant is a true unity for mathematicians and aftronomers, as is well known 

 to all that cultivate the fciences ; fecond, becaufe the magnitude of the circumference of 

 the 6arth is known to us only by conje£lure. All the great ailronomical and geodefial 

 undertakings have been performed in the northern liemifphcre. We have yet no correct 

 notion of the figure of the fouthern hemifphere. It would even rcfult from the obferva- 

 tions of Lacaille, at the Cape of Good Hope, that the tcrreftrial fphcroid is more flattened 

 on this fide, l^o hypothefis can be admitted in a fubjecl of this nature. The learned 

 could therefore propofe as a fundamental unity that only which was well known to them» 

 namely, the diftance from the north pole to the equator. 



This diflaiice is obtained with certainty from the meafure of an arc of the meridian in- 

 terfered by the forty-fifih parallel. France alone olTers in a civilifed country an arc ofthe 

 requifite magnitude, whicli, if we comprehend a fmall p.irt of the Spanifh territory, termi- 

 nates in the fea at both extremities. This arc has befides the advantage to have been re- 

 peatedly meafured with the utmoft care. Two celebrated aftronomers are at this moment 

 employed on this operation ; not that it is prefuraed that the refult of their labour can havx; 



' We reckon S6400 fccoiiJs in a day; becaufe the day is divided into 24 hours, and the hour into 60 mi- 

 nutes. Eveiy other divifion would render the element of time longer or fliortcr, and accordingly influence the 

 length of the peodulum. The pendulum which Qiauld make one hundred thoufand ofcillaiions in a Jay, would 

 b; only 2.28J feet in length, whereas the pendulum for I'econds is three feet 7.11 lines under the equator. C. 



All the meafurcs in iWn psper ;nuft be undcrftood to be French, as I have tliought it unnecclVary to make 

 «ny other reduftions but ihofe in the table p. 199. N. 



■f Under the name of geographical meafures we denote in this place the degrees of latitude and longitude. 

 It is commonly fuppofed that a degree of the meridian is twenty-five common leagues ; but in order to afford 

 this accurate quotient in rouad numbers, it is neceffary to reckon the league at from iiSi to 2285 toifcs. The 

 league cannot be at tli« fame; tirn? a multiplei of the pendulum in round numbers, andean ahquot part of a 

 degree. C. 



J This notion fecms to have ptcfente.d itfcif to the ancients. There are fatiifaflory proofs that the cubit of 

 the Nilometcr in Egypt, the length of which is 1.712 foot, was contained four hundred times in a fladium, two 

 hundred thoufaiid times in a degree, and confcqucntly feventy-two millior.s of times in the circumference ofthe 

 earth, ft is tiiought that the great Pyramid is a monument of this fyflem, and that its bafe is cxa£lly the length 

 of the ancient Ej;ypiian ftadium of five hundred to the degree. The ancients had neverthclcfs neglefled to 

 adf>pt an uniform method of divifion, and iii this their notion required improvement. The fame obfervation may 

 be made on the fyftcm of meafures hkcwifc propofcd to be deduced from the magnitude of the earth, in the 

 year 1670, by Mouton, an afttonomcr of Lyons. He thought it neceffary to prcfervc the divifion of a circle 

 into three hundred and fixty degrees, and the degree into fixty minutes; fo that he does not propofe the de- 

 cimal divifion but from the minute of the meridian. The thoufandth part of the minute of the meridian affijrdt 

 a mtafure of five feet eight inches and a half, which he pri^poles for the ufual unity. C. 



7 =""/ 



