452 THE MOUNTAIN. 



which produce moisture in one country and drought in an- 

 other in its vicinity, the former, when the country is on the 

 side of the mountain against which the rain- winds blow, and 

 the latter, when the country is on the opposite side of those 

 mountains. 



In Johnston's Hyetographic, or Rain Map of the World,* 

 we are presented with a division into the three important 

 zones of precipitation. The first is the zone of the peri- 

 odical rains, extending both sides of the equator to the 

 tropics of Cancer and Capricorn. This includes the sub- 

 ordinate zone of " frequent, almost constant, precipitation, 

 always accompanied by electrical explosions." This is a 

 narrow belt of from 5 or 6 width, near the equator. 

 The greatest precipitation occurs in this belt, amounting, 

 according to Johnston, at one point on the western coast 

 of Africa, to "upwards of 300 inches, or twenty-five feet, 

 which frequently falls during one season alone." 



The other two are the northern and southern zones of 

 constant precipitation. 



"The zones of constant precipitation are so named in order to dis- 

 tinguish them from those of periodical rains. In the former, it does 

 or may rain during every day in the year, whereas, in the latter, 

 during many months, not a drop of rain falls." JOHNSTON. 



These northern and southern zones of constant precipi- 

 tation extend to the arctic and antarctic circles. There are 

 rainless districts in all these zones ; stretching around the 

 earth in different latitudes, they are generally, however, 

 within or near the tropics. Within these zones of precipi- 

 tation there are, as suggested in the quotations from John- 

 ston's Physical Atlas, various causes for irregular distribu- 

 tion of the quantities of rain in different parts of the earth's 

 surface. 



On this subject, Schouw, of the University of Copen- 

 hagen, has the following remarks : 



"Another principal cause of the increased quantity of rain, lies 

 in the inequalities of the earth's surface. Mountains increase the 



* Johnston's Map is VERT far from correct for the American continent. 



