372 



HYDROGRAPHY. 



the Tropics. At the same time, it will be observed that the prepon- 

 derance of these heated waters lies in the northern hemisphere. 



It would be foreign to the subject in this place, to institute the 

 inquiry, Whence do these waters derive their heat ? But the question 

 may be so far answered, that this heat cannot be wholly from the 

 sun ; and it may be questioned if his heating rays have any other effect 

 upon them than to increase the evaporation. 



Many philosophers assert that what heat is derived from the sun's 

 rays is again returned to the air by radiation. If such is the case, it 

 is not by accumulation from that source that this heat can have been 

 originated. 



How great must be the evaporation which is constantly taking 

 place, both by day and by night, from these heated waters ; and what 

 an immense rarefied area is here exhibited to view, to destroy the 

 equilibrium in the atmosphere, and generate the vapors ! In it we see 

 ample cause for the wonderful effects which we witness in the pheno- 

 mena under consideration, and which must continue so long as the 

 same cause prevails. 



It is thus evident that on this planet we have a continuous belt of 

 heated water around the globe. 



If we recur to authorities, we are informed that the air is an elastic 

 fluid, acted upon by the same laws of gravitation as the more solid 

 particles of matter. Consequently it will remain at rest from its vis 

 inertia, provided an equilibrium of temperature is insured, and will be 

 carried with the earth in its revolution. 



That the rotary motion of the earth cannot have any effect upon 

 the surface currents of air, is also fully evident, by the fact of the 

 prevalence of westerly winds at the same time that we have easterly 

 winds within the Tropics moving in opposite though parallel direc- 

 tions. Now, if this rotary motion was felt in one direction, it ought to 

 operate in the other, and to produce a westerly wind, to be felt on the 

 surface at the Equator, moving at the rate of 1000 miles per hour, it 

 would be necessary for the wind to have greater velocity. This will 

 be readily seen to be impossible ; for the greatest velocity that wind 

 has been known to attain in a hurricane, is short of a hundred miles 

 in the same time. We therefore consider that the earth must 

 carry with it in its revolution a large part of the atmosphere, which, 

 undisturbed by heat, would remain quiescent, and be free to move in 

 any direction. If this were not the case, none but easterly winds 



