70 OUTLINES OF NATURAL PHILOSOPHY. 



the globe. See Memoirs sur la Projection des 

 Cartes Geographiques, par M. HENRY, 4to, Paris, 

 1810, chap. 8me, p. 55., & c . 



73. The construction which is called MERCA- 

 TOR'S Projection, is chiefly used for nautical 

 charts. In it the meridians are parallel lines j 

 the degrees of longitude are all equal ; the pa- 

 rallels of latitude are also parallel lines ; and the 

 degrees of latitude increase on the chart in the 

 same ratio that the degrees of longitude dimi- 

 nish in the sphere, or in the spheroid. 



a. The consequence of making the degrees of latitude 

 increase, in the manner described, is, that the de- 

 grees of latitude and longitude bear to one another 

 the same ratio in this chart, that they actually do on 

 the surface of the earth : and as the meridians are 

 all parallel, the rhumb-lines, or the lines of azi- 

 muth, are straight lines. Hence the great use of 

 this construction in navigation. 



b. This very ingenious contrivance is alluded to, 

 though obscurely, by PTOLEMY. It was first used 

 among the moderns by MERCATOR, whose name it 

 bears ; but the principle of it was first explained by 

 ED. WRIGHT in 1599, who shewed that the parts 

 into which the meridian is divided, must be in- 

 versely as the cosines, or directly as the secants of 

 the latitude ; and he taught how it might be con- 

 structed 



