REFORMATION OF CARTOGRAPHY IN FRANCE 129 



meridian ; (4) the planned survey of the whole country, de novo, 

 based on a complete system of triangulation, which resulted in 

 the celebrated Cassini Survey. This had been advocated by 

 Picard as early as 1681. 



A remarkable contribution to this work was made by the four 

 generations of the Cassini family. The first, Jean Dominique, 

 who was invited to work at the Paris observatory in 1669, 

 assisted in the determination of the meridian, but his greatest 

 service to cartography was his perfection of a method of deter- 

 mining longitude by observation of the movements of Jupiter's 

 satellites, a great improvement on the method of lunar eclipses, 

 though the probable error was one kilometre. After the early 

 work on the meridian, it was resolved to apply the new methods 

 to rectifying the map of France, and Picard with other sur- 



Flandre 



c Amtcii9 



PARIS paraUeU Je Parii 



§2 



lionf 



Lanquedoc . .- 

 MontpelUcr J^ 



Provence ^ 



Batjomttf 



^/orbotin; 



V/^ 



France, from the 'Carte de France corrig6e . . . sur les observa- 

 tions de MM. de I'Acad^mie des Sciences', 1693, showing the 

 revised position of the coast-line 



