30 POPULAR LECTURES AND ADDRESSES. 



suppose you were to cut the skin into countless 

 liths, and then cutting it open across one point of 

 the equator, lay it flat and fill up the spaces 

 between the liths : then you have a plane drawing 

 or chart of the earth's surface such as the ac- 

 companying diagram, Fig. 7, shows. You have 



so 



20 



60 



40 



20 20 



FIG. 7. Plane Chart. 



stretched the polar regions in longitude without 

 altering them in the north and south direction. 

 Stretch them now polewards north and south to 

 the same proportionate extent as you have already 

 stretched them in longitude. By doing so you 

 put the north and south pole away to an infinite 

 distance and lose the polar regions, but you thus 



