344 



Wilbrand and Ritsen^s 



some parts where the snow melts, and exposes the surface 

 rocks or soil a part of the year. There minute lichens adhere 

 to the surface, and animals, chiefly insects and birds, are occa- 

 sionally found ; but where the surface is enveloped with eter- 

 nal snow, vegetation ceases, animals die, and the inquisitive 

 disposition of man terminates. 



' " But besides this perpetual line of snow, there is another, 

 constantly varying according to the seasons. In the northern 

 hemisphere, after the autumnal equinox, this line gradually 

 becomes lower; being in the winter, according to circum- 

 stances, even in the middle of the temperate zone, at the level 

 of the sea; on the contrary, in the southern hemisphere, as 

 the sun reaches the southern tropic, the line rises, till it joins 

 the perpetual snow ; and as the sun returns towards the 

 northern tropic, it again gradually descends towards the sea. 

 Thus organic life fluctuates perpetually from north to south, 

 and from south to north. It is this varying line of snow which 

 intimates to birds of passage their time of migration," 



In the picture, the detached mountains, as well as conti- 

 nuous ranges, which are, in the five parts of the globe, elevated 

 above the perpetual line of snow, are delineated according to 

 their latitude, and their names and height are marked on them ; 

 but of course in such a picture it is impossible to give any 

 idea of their longitude. Thus the Himalaya Mountains of 

 Asia {fig, 103. c), the highest in the world, are placed between 



