NA VI G A TION. 



get a very convenient chart for the middle and 

 tropical regions, which is called Mercator's pro- 

 jection. It is illustrated in the annexed diagram, 

 Fig. 8. Contrast the shapes of Greenland as 

 shown on these two charts, Figs. 7 and 8, with 



50 



40 20 20 40 60 



FlG. 8. Chart on Mercator's Projection. 



one another, and with that shown on the magnetic 

 chart of the northern hemisphere, Fig. 5 (p. 22\ 

 which is more nearly the true shape than either. 



A " great circle " of the earth's surface is a circle 

 whose plane passes through the earth's centre. 

 Any diameter of the great circle measured along 



