Appendix II 



353 



on a conical projection. Those of the British Islands (Plates IX. X. 

 etc.), for example, are on a conical projection; the meridians con- 

 verging to the proper degree and the parallels being arcs of circles. 

 If a cone of transparent paper were placed over an artificial globe 

 (Fig. 67) and the lines traced through, a map of this kind would 

 result ; the distortion being greatest at the greatest distances from the 



FIG. 67. Conical Projection. The left hand figure represents a cone placed on 

 the globe, the surface features of which are projected, as in Fig. 66, by lines 

 drawn from the centre. The right hand figure shows the cone unrolled 

 showing the parallels as semicircles and meridians radiating from a centre. 

 The double lines show a map cut from the developed cone. 



parallel along which the cone touched. When the cone is supposed 

 to cut the globe along two parallels, the resulting map is much more 

 accurate. In actual map-making the distance and curvature of the 

 parallels and meridians for each projection are ascertained by mathe- 

 matical calculations. 



446. Contour -lines are drawn on maps to express differences of 

 level in an exact manner. 

 They express the height of 

 the land in the same way as 

 isotherms express the tem- 

 perature. Each contour-line 

 represents a string of figures 

 of elevation having the same 

 value. The sea -coast is a 

 natural contour - line, and 

 raised beaches are natural 

 contour-lines etched on the 



hill -sides. Every contour- 

 line represents the coast- 

 line that would result, if 



FIG. 68. Contour-lines. The Line BC re- 

 presents sea-level, each of the inner lines 

 represents a level 100 feet higher than that 

 next to it on the outside, the line round A 

 being 500 feet above the sea. The scale 

 below refers to horizontal distance. 



the sea rose to that level. When 



contour-lines are far apart the gradient or slope is gentle ; for ex- 

 ample, along AB (Fig. 68) we could advance nine divisions of the 

 2 A 



