WINDS. 



391 



within their range parts quickly with its moisture, leaving it entirely 

 blighted. 



Hot winds, so called, are liable to mislead us. If they could be 

 traced, they would be found to be tending to areas of still higher tem- 

 perature ; and it is well known that they are comparatively local ; — 

 but many are so called from being dry and suffocating, rather than 

 hot. We judge of them from our feelings, rather than test them by 

 means of our instruments. 



At other times, the Monsoons often unite with the Trades, and 

 flow in a common direction, and, where the one wind is warmer than 

 the other, they are found to commingle and produce precipitation. 



On the ocean, where the areas of high temperature exist, the air 

 generally flows towards them from all sides, though with greater or 

 less velocity. In the Atlantic and Pacific Oceans, we have two very 

 remarkable nuclei of heated water, where the temperature ranges 

 nearly to 90°, and through which the Equator of heat passes. To 

 these the air tends, although only a few degrees above the surround- 

 ing temperature; and the currents of air, after the equilibrium is 

 restored, cease to move in any horizontal direction, when calms 

 ensue. These areas of calms have various positions, but they always 

 exist where the heat is equable, and generally hold a midway position 

 between the Trade Winds, or between these and the variables. In 

 both cases, they change to and fro, vibrating through a few degrees of 

 latitude. 



The calms, therefore, are the result of the restored equilibrium, and 

 they endure as long as there is no disturbance produced by a change 

 of temperature. These calms are another proof that the earth in her 

 rotation produces no friction to affect motion on the air, and that the 

 air moves with it. In the northern hemisphere, where they prevail 

 during the summer months, the temperature is generally equable. In 

 all places where they exist within the Equatorial belt, frequent local 

 gusts of wind, of short duration, are experienced from every quarter. 

 There the warm air ascends rapidly, evaporation and condensation 

 take place, and explosions of electricity, with rain, are frequent. The 

 period when these occur most frequently is during the season when 

 the sun is vertical, and his action most powerful. 



The intertropical seas being occupied by these large areas of 

 heated water, light winds and calms must prevail, as the air can flow 

 no faster towards them than it ascends to the upper atmosphere. 



