Meafure of the Meridian in France^ &c. 321 



The precifion with which the angles were obferved is fuch, that out of ninety triangles, 

 which coniiefl; the extremities of the meridian, there are thirty-fix in which the fum of the 

 three angles differs from its proper quantity by lefs than one T-cond ; that is to fay, in which 

 the error of the three angles taken together is lefs than one fecond : tliere are 27 triangles in 

 which this error is lefs than two feconds; in 18 others it does not amount to three feconds ; 

 and there are four triangles in which it falls between three and four feconds, and three tri- 

 angles only in which it is more than four, but lefs than five feconds. It may be doubted 

 whether a greater degree of accuracy be obtainable, pai-licularly in the country where the 

 operations were performed ; and accordingly it may be fuppofed by thofe who confider thefe 

 tables without being informed of the manner in which they were made, that this appearance 

 of precifion may have been given by management and fubfcquent corredlion ; but ihe ori- 

 ginal regifters of the obfervers, the refults which they themfelves fent to Paris, long before 

 the bafes were meafured, and at a time when they were ftill bulied with their operations, 

 and the labours of the commiffioners the tifelvis, prove the contrary in the mod authentic 

 manner. No arbitrary or conjectural corredtion, however flight, has in any cafe bsen made; 

 and all the tingles have been determined from confiderations derived from the obfcrvations. 

 themfelves. 



Two bafes were meafured by Cit. Delambre; one between Melun and Lieufaint, the oihet 

 near Perpignan, between Vernet and Salces. The care and precaution with which thefe 

 operations were performed, and the means ad-pted for that purpoie, are detailed at full length 

 by Cit. Delambre, in his Memoir already mentioned. The inftruments were four rods 

 of platina, conftrufted with great care by Citizen Lentlre. from the inftrudions, and under 

 the infpedlion of Citizen Borda. Each of thefe rules is covered to within four inches of its 

 anterior extremity with a fimilar plate of brafs, .novable in the diredlion of the length of 

 the rule of platina, and fixed to it by the extremity which is moll remote from the unco- 

 vered part. This plate of brafs forms, by the dilieient dilatations which the fame variation 

 of temperature produces in the brafs and the platina, a very fenfible metallic thermometer, 

 the dimenfions of which are engraved upon the anterior extremity, which carries a ver- 

 nier and a microfcope to afcertain the fubdivifions. Before thefe rules were ufed a number 

 of experiments were made to afcertain their dilatation, the ftate and motion of the metallic 

 thern.oireters, and their comparifon with the ordinary thermometers. The lengths of the 

 rules, Nos,. 2, 3, and 4, were compared with that of No. i, to which all the nicafures were 

 reduced, which for that rcafon was called the original (le module) ; which comparifons were 

 made with fuch accuracy as to have no doubt of the two hundred thoufandth part. Citizen 

 Bo: da has delivered to the commiffion a memoir containing a detail of all his experiments, 

 which will form an eifential and interefting part of the colieflion to be publifhed refpefling 

 this great op?ration. 



1 hefe rules v/ere placed in proper cafes, to fecure them for every external aftion or flexl^re 

 without checking their expanfion or cofltra(Sion, as well as to defend them from the rays 

 of the fun, &c. 



Every 



