250 PHYSIOGRAPHY 



Indian Ocean had great influence on the early trade in India. 

 Vessels sailing from Europe used to time their outward voyages so 

 as to take advantage of the southwest monsoon, and their return 

 voyages so as to take advantage of the northeast monsoon. 



3. Mountain and valley breezes. Winds due to changes of tem- 

 perature sometimes blow about mountains. Mountain-breezes 

 blow from the mountains at night, and valley-breezes blow toward 

 them on sunny days. 



Mountain and valley and land and sea breezes, and monsoon 

 winds are not the only ones due to differences of atmospheric tem- 

 perature, but they afford the simplest illustrations of air move- 

 ments due to this cause. 



Vertical movements and temperature. When air rises it ex- 

 pands, and as it expands it becomes cooler. When air descends it 

 becomes denser and warmer. These changes of temperature have 

 an important influence on rain, snow, etc., and will be considered 

 in connection with those topics. 



