456 APPENDIX 



without modification only on those days ; but since the 

 angle of the sun above or below the plane of the equator is 

 given in the Nautical Almanac for every day in the year, 

 by adding this angle to the angle BAI when the sun is 

 above the equator, and subtracting it when the sun is be- 

 low the equator, the latitude of a place can be found for 

 any day. 



On board ship, every fair day, the officers will be seen 

 just before noon coming on deck with their sextants to 

 take the elevation of the sun. They find the elevation 

 several times until they are sure that the sun has reached 

 its highest point, and. at this moment they call for the 

 time to be taken on the chronometer; for w r hen the sun 

 reaches its highest point, it is noon for that place. Thus 

 by making use of this one observation they are enabled, 

 with the help of the chronometer, to find both their latitude 

 and their longitude, or their exact position on the earth. 



218. Topographical Maps. Maps which attempt to show 

 the surface features of the earth are called topographical 

 maps. There are several ways in which we may try to 

 show on a map the irregularities of the surface. One of 

 these is shading, that is, making the hills and ridges light, 

 while the valleys are shaded dark. A somewhat similar 

 way is to draw short broken lines in the direction of the 

 slopes. This gives a more accurate representation of the 

 steepness of the descents, since the lines are made short 

 and heavy when the slope is steep and longer and lighter 

 when it is gradual. Such maps are called hachure maps. 



The commonest way in this country is to draw lines 

 connecting places of equal elevation. These lines wander 

 in and out of the valleys and around the hills, but always 

 pass through places which are of the same altitude... The 

 distances apart of the lines vary continually, but the eleva- 

 tions never. From these maps the height of any place can 



