ASTRONOMY. 71 



s.tructed by the addition of the secants of a series 

 of arches taken in arithmetical progression. 



It was afterwards observed, that the meridian line 

 thus divided, was analogous to a scale of loga- 

 rithmic tangents of the half- complements of the 

 latitudes ; this was at first only known as a fact, 

 but was afterwards demonstrated by JAMES GRE- 

 GORY, in his Exercitationes Geometric*?, 1668* Dr 

 HALLEY proved the same in a more concise man- 

 ner, Phil. Trans. N 219., and greatly improved 

 the construction of the chart. 



For other methods of constructing maps and charts, 

 see VARENIUS, Sect. iv. chap. 32. Encyclopedic 

 Methodique, art. Cartes. LORGNA, Principii di 

 Geogrqfia, 4-to, Verona, 1789. Traite de Topo- 

 graphic, &c. par L. PUISSANT, Liv. n. LA 

 GRANGE, Mem. de Berlin, 1779. 



SECT. 



