WINDS. 



385 



the impulse of motion in either direction is changed or ceases, and 

 the vis inertia of the body of air destroyed. 



Now, in the region lying to the north and south of these areas of 

 calm, it is found that the temperature of the ocean is higher in the 

 summer months of the two hemispheres, and that there is in conse- 

 quence a flow of air from it towards the parallels a few degrees to the 

 north and south ; — those in the northern hemisphere veering from 

 the southwest to the southeast by the south, whilst those in the 

 southern veer from the northwest to the northeast by the north. 

 These currents of air frequently coincide with the general direction 

 of the variable winds in higher latitudes, the flow of which is simply 

 induced by the difference or variations of temperature, as shown by 

 the isothermal lines of the oceans lying between the old and new con- 

 tinents in either hemisphere, combined with the heating of the sur- 

 faces of those continents during one portion of the year, which 

 induces the flow towards them to be the greater. When they cool, the 

 flow returns from them to the ocean, and this creates as well as gives 

 direction to the alternate flow of currents of air familiarly called the 

 variables, and with which the rotation of the earth can have nothing 

 to do. The Polar winds, in like manner, circulate, caused by the 

 unequal distribution of heat, and by the rays of the sun during his 

 semi-annual sojourn, as well as the evolvement of heat in the con- 

 densation of vapors, and the changes of water into ice. The order 

 of these movements is simple and effective in producing a thorough 

 interchange and commingling of the atmosphere, and results wholly 

 from the one great natural law which has been given to it by an All- 

 wise Providence. 



Having traced out the aerial currents on the surface, we will now 

 take up those of the upper regions, which the theories quoted in the 

 first part of this chapter represent as setting towards the Pole, " for 

 the purpose of restoring the equilibrium, and drawing off the accumu- 

 lation which would soon exist at the Equator, as well as to ameliorate 

 the climate by diffusing heat around the Poles." 



In confirmation of this upper-current theory, it is stated that the 

 winds pass in a constant current from the southwest and northwest ; 

 but this, it appears, is only an inference from induction, — that there 

 must be a return current to replace the air coming from the Poles, 

 which otherwise would soon be without atmosphere. Where is the 

 proof that these winds do prevail, and are constant ? 



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