32 THE CLIMATE OF AUSTRALASIA 



CHAPTER I. MONSOONAL WINDS AND 

 RAINFALL. 



WE must therefore, briefly consider the effects 

 of an ocean on the climate of the adjacent 

 lands. It is well known that water has a higher 

 specific heat than land ; that is to say, it 

 requires more heat (the ratio is about 5 to i), 

 to raise one pound of water one degree in 

 temperature than to effect the same change in 

 one pound of earth. Moreover, while water is 

 more slowly heated on exposure to the sun, it 

 gives off its heat more slowly. Thus in the 

 case of equal areas of land and water, each 

 receiving precisely the same amount of heat 

 from the sun, the land becomes the hotter 

 during the daytime and cools the more quickly 

 at night. As in summer the days are longer 

 than the nights, it follows that land will, on the 

 whole, be warmer in summer, and colder in 

 winter, than water adjacent to it. 



Any area, which is warmer than the air above 

 it, will give off some of its surplus heat to 

 the air in contact with it ; the air being heated, 

 expands, and thus becomes lighter and rises as 

 a warm ascending current. Cool air from the 

 surrounding areas accordingly blows in to take 

 its place, and, over these cooler areas, there is 

 a descending air current, which, on reaching 

 the earth's surface, flows to the warmer area. 



