2jro Method employed in Ptanck 



to fix invariably the ftandard of the metre *, two celebrated 

 aflronomer6, Delambre and Mcchain, were commiffioned to 

 meafure an acre of the meridian, by a feries 6f triangles 

 carried from Dunkirk to Barcelona f. To calculate the fides 

 of thefe triangles, it was necefiary to fet out from a primitive 

 bafe. None of thofe meafured for the meridian of 174c* 

 had been determined with fufficient accuracy, and fomc 

 errors were fufpec~led. As the bafe fieareft to Paris, between 

 Villejuif and Juvify, prefented a length of little more than 

 5000 toifes Xt with confiderable inequalities of the ground ; 

 the road from Lieufaint to Melun, which gave a length by 

 eftimation of 6076 toifes, in almoft a ftraight line and with 

 very little variation in the level, was with great reafon pre- 

 ferred. To prepare for the meafurement of this bafe, the 

 two fignals or obfervatories, now to be feen, the one at the 

 end of Lieufaint, and the other at the entrance of Melun^ 

 were firft erected. Within each of thefe fignals a large 

 {tone was fecured in a piece of ftrong mafon-work, and from 

 this ftone arofe a cylinder of copper, faftened into it wich a 

 mafs of lead. The axes of thefe cylinders, which were 

 fourteen lines, in diameter, correfponded perpendicularly 

 with the upper points of the fignals. As the line of the bafe 

 formed towards the middle a fmall bending, the angle was 

 meafured, and found to be 179 n', which produced in the 

 total length a difference of 10^ inches. Departing from the 



• See the preceding tabic of the new French meafures. Edit. 



f It was propofed to extend this labour to Majorca; but it was found 

 impoilible to proceed to that Ration, on account of the too great diftance 

 of the fignals. 



% The object of Delambre and Mechnin's labour being to cftablifh ? 

 relation between the old and the new meafures, and this labour having 

 been begun in 1791, it was necefiary that the meafurement ihould be ex- 

 preffed in toifes, and fractions of a toife ; the ufe of which could not be 

 abandoned till the metre was exactly determined. The commiflion of 

 weights and meafures gave, according to the ancient mode of calculation, 

 a provilional metre, the approximation of which is more than fufficient for 

 common ufes. This metre furpaffes the half toife by 11.44 line*. 



fummit 



