1Tt Mom 83 



the normal condition in summer is that of a 

 breeze from the ocean toward the land during 

 part of the day and a corresponding breeze 

 from the land to the ocean during part of 

 the night, with a period of no wind during 

 the morning and evening of each day. 



The forces that work to produce all the 

 varying phenomena of air currents on differ- 

 ent portions of the earth are difficult to ex- 

 plain, as there are so many local conditions of 

 heat and cold, and these are modified by the 

 advancing and receding seasons. The un- 

 equal distribution of land and water upon the 

 earth's surface ; the readiness with which some . 

 portions absorb and radiate heat as compared 

 with others; the tall ranges of mountains, 

 many of them snow-capped; the lowlands ad- 

 jacent to them that become intensely heated 

 under the sun's rays; the diversity of coast- 

 line and the fact that there is a zone of con- 

 tinually heated earth and water in the tropical 

 regions all these conditions, coupled with the 

 fact that the earth rotates on its axis once in 

 twenty-four hours, are certainly sufficient to 

 account for all the complicated phenomena of 

 aerial changes on the various portions of the 

 earth's surface. 



The trade winds are so called because they 

 blow in a certain definite direction during cer- 

 tain seasons of the year, and can be reckoned 

 upon for the use of commerce. If you trace 



