PRACTICAL EXEBCISES IN GEOGRAPHY 65 



But when the earth is stated to he very small in comparison to the 

 distance to the stars, the two parts of the sky separated by a horizon 

 plane will be recognized as equal. The horizon planes of observers 

 at different points on the earth will cut the sky into different halves, 

 as may be shown by the aid of a haiid globe. The uneven border of 

 the sk}^ against hills should be called the sky-line, not the horizon. 

 All this is as much astronomy as geograph}^ ; but it is all essential to 

 the clear understanding of matters that are constantly taught in geog- 

 raph}^ such as latitude and the seasons ; no safe entrance into such 

 matters can be made without careful attention to fundamental con- 

 ce})ts. 



The discovery, attributed to Eudoxus, that an observer, traveling 

 north or south, sees that stars change their position with respect to 

 his horizon, will be considered in connection wdth measures of the 

 size of the earth further on. 



The causes and consequences of the earth's shape are better pre- 

 sented in the text than in practical exercises. Among the consequences 

 are the essentially uniform value of gravit}^ at all points on the earth's 

 surface, and the absence of immense ascents and descents that must 

 occur on an earth of any other shape. The nearly globular form of 

 the actual earth has been of enormous importance during long past 

 ages in facilitating the migration of plants and animals from one 

 region to another, and in recent centuries in permitting the migrations 

 of mankind and the development of commerce. 



Rnldlion. — ^The vague ideas in the minds of adults regarding the 

 earth as a rotating globe suggest that no good ground w'as provided 

 in their school da^^s for a correct understanding of this fundamental 

 proljlem. The })roljlem pertains equally to geography and to astron- 

 omy ; ])\\i as it should be encountered before these two suljjects are 

 differentiated, it is naturalh^ classified under the first and more usual 

 school subject. Very simple apparatus suffices. A pointer, ]nvoted 

 at one end and sighted at the sun at different hours through the da}^ 

 enables a young observer to gain a definite idea of the sun's (api)arent) 

 dail_y iiioveniont across the sky. (Actual sighting at the sun is not 

 nece.ssar}' ; when the pointer is held so that its shadow is no larger than 

 its cross-section, it is i)roj)erly directed.) Record of successive obser- 

 vations may 1)6 made by setting up stakes so thattludr tops sliall just 

 touch the end of the pointer in the successive sights at the sun. On 

 the f(jllowing day the sun n)iiy l)e seen again in the earliest position 

 oliservod on tlie first daw tlic period thus measured heini'- a natural 



