LEVELS OF FRANCE. 219 



vertical lieJglit which they are elevated above the furface ofv«ticale)evat;ori 

 ,, above the fea ca 



the ocean. ^ jts ,3^,^^^^ ^^^ 



The obje6i of this memoir Is to indicate the means of deter- longitude. 



mining this vertical heighth, by their particular application to Management 

 ,, , .. CT? proper for afcer- 



Ihe territory of France. taining d^efe po- 



It is evident, that all the operations neceH^ary for this deter- fitions /hewn in 

 mination, may be reduced to a feries of levels made in deter, p^.^jj"^^^"''^ °*^ 

 minate dire6iions. 



Nature itfelf has pointed out thefe dlretSlions, by the lines 

 of grealefi declivity, which the large rivers, and ihofe which 

 flf)w into them, form on the furface of the earth. 



Thus, France being divided into five principal bafons, by The levels of 

 the Rhine, the Seine, the Loire, the Gironde, and the Rhone, ^j^g^j of^Francc 

 — the levels of the courfe of thefe rivers, from their fources, would form the 

 or from their entrance into France, to their terminations >" ratbn'for thT" 

 the ocean, would form the firft bafis of the work propofed to country. 

 be undertaken. 



After having afcertained this firft bafis of the general ope- The levels of 

 ration, the levels of the ftreams by which the great rivers are which fuppjy 

 fupplied, (hould be next taken, and thefe ftreams (hould be thofe great rivers 

 confidered without any regard to thofe of the third order, by ^^^^^ ''* "**^ 

 which they are themfelves maintained. 



At the fame time, the levels of the rivers of the fecond The levels of 

 rank, which fall into the two feas, fliould be taken ; fuch as fg^ond rank 

 the Efcaut, the Somme, the Orne, the Vilaine, the Cliarente, taken at the fame 

 the Adour, the Herault, &c. ihTfirft!^"^' '' 



The declivities of the beds of the fecondary rivers being The levels of 



known, thofe of the rivers of the third, fourth, and fifth or- '!*'.^" "/ ^^""^ 



third, fourth, 

 ders, &c. ftiould be determined lucceffively, according to and fifth order, 

 fpecial inftru61ions which ftiouid be given for this purpofe. taken. 



By thus clalfing the operations relative to the general levels 

 of France, and by arranging their refulls in order, as they 

 were obtained, all the data would be foon collefled, which 

 were neceflfary for tracing the elevation of its territory on a 

 geographical chart already prepared. 



This tracing of the elevations would be effefled, by joining ^''^Y^^'O" °^ ^^^ 

 ... , , , , r ,. fiiffa" of 



all the points on one level by the lame Ime. France to be ex- 



Thefe lines of kvda might be fuppofed to be elevated per- prefled in the 

 pendlcularly, one above the other, by a determinate fpace, [ng all'the poir"s 

 conformable to the fcale of the chart on which they were on one level by 



, the fame line. 



traced. 



