WINDS. 



.7/19 



and may possibly be assisted by the rotation of the earth. This flow 

 continues constant, though invisible, throughout the year, from the 

 water to the land. The temperature of the ocean, we know, remains 

 nearly the same, but the land is subject to great variations. So long 

 as the temperature continues the same, the vapor is held suspended ; 

 consequently, we have but little rain on the ocean ; but when it en- 

 counters the land, if the heat over it is greater, it is expanded and 

 passes on ; if less, condensation takes place, and precipitation ensues. 

 Thus the supply is afforded in inexhaustible quantities in the most 

 simple way, — one that is alone dependent upon a change of tempera- 

 ture. From these causes a greater quantity of rain falls near the 

 coasts, decreasing towards the interior of continents, and rains of 

 shorter or longer periods are produced. Local winds and even fresh 

 gales are the result of the heat evolved by the condensation of the 

 vapor, which forms large rarefied areas, into which the denser air 

 flows with greater or less velocity. 



According as the air is more or less surcharged with vapor, are we 

 liable to have rain. The clouds are the evidence of the presence of 

 vapor; they form and disappear at times rapidly. This is the result 

 of the ascending and descending currents. 



Within the tropics, when the sun is passing over the zenith of any 

 parallel, it has been found that the rainy season prevails. It is ex- 

 plained by the fact that the evaporation at that time is greater, and 

 the atmosphere more saturated; condensation takes place more easily, 

 and the rain is more copious. It is remarkable, that when it is the 

 rainy season in the Tropics, the rains occur only during certain hours 

 of the day, and that the nights are cloudless. The part of the twenty- 

 four hours in which the condensation and precipitation take place, is 

 after the sun has passed the meridian. Now, under the hypothesis 

 that the vapor is left behind by the rotary motion of the earth, we have 

 a ready explanation of this phenomenon, and some idea may be had 

 of the velocity of the retardation of vapor. Let us suppose the width 

 of the ocean which lies to the eastward of the place where this pheno- 

 menon occurs, an arc of the earth's surface, from which the evapora- 

 tion has arisen ; and the time the rains fall, to represent the condensa- 

 tion of the same vapor — the difference between these will give the 

 time of the retardation. 



There are several localities within the Tropics where this phenome- 

 non occurs, and where the rain falls for five hours. The width of the 



