52 



llanos, combined with the observations of the 

 pendulum, as interesting to science alone; they 

 are at the same time the principal bases of maps, 

 without which any regular administration of the 

 affairs of a country is impossible. Hitherto this 

 has been necessarily limited to a simple astrono- 

 mical sketch ; this being the surest and most 

 ready means on a surface of large extent. At- 

 tempts have been made, to determine the longi- 

 tude of certain points on the coast and in the 

 interior in an absolute manner ; that is, by celes- 

 tial phenomena, or series of lunar distances. 

 The most important places have been fixed 

 according to the three coordinates of latitude, 

 longitude, and height. The intermediate points 

 have been deduced chronometrically from the 

 principal points. The very uniform movement 

 of the chronometers in the boats, and the 

 strange inflexions of the Oroonoko, have facili- 

 tated this connection. By bringing the chro- 

 nometers to the point of departure; or by ob- 

 serving twice, going and coming, at an interme- 

 diary point, joining the extremities of the chrono- 

 metric lines* at two places very distant from each 



* I mean by this expression, perhaps improper, the lines 

 that unite points, the longitude of which has been determined 

 by means of the chronometer, and which are consequently 

 dependant on one another. It is on the proper disposition of 

 these lines, that the precision of a measurement merely as- 

 tronomical depends. 



