HUTCHISON'S OBJECTIONS, WITH REPLIES. 457 



begin to form, if continued, must increase their density un- 

 til rain is produced. 



Again, if clouds and rain be produced only by an upward 

 vortex of air, (supplied by converging currents below the 

 clouds, and disposed of by diverging currents above them,) 

 which, according to your theory, has the power of perpetu- 

 ating itself; when once begun, it should become a sort of 

 perpetual motion, that could not by any possibility come to 

 an end. But instead of this being the case, we find that 

 all rains terminate. 1 



2d. If you state that upward vortices must be occasioned 

 during day, by the atmosphere nearest the surface of the 

 ground becoming then much more heated than the aerial 

 strata above, the following and similar objections present 

 themselves : 1st. How does more rain fall during night than 

 during day ? 2d. How does it never rain in Egypt, where 

 the wind blows almost incessantly from the north, that is, 

 from a cold towards a comparatively warm climate, and 

 from the sea towards the land? According to your theory, 

 the cold saturated air from the Mediterranean should have 



1 When a lofty cloud is once formed, it certainly has a self-continuing 1 

 power; and accordingly, we find that many storms originating in the West 

 Indies, have continued for many days and nights in succession, and travelled 

 many thousand miles from the place of beginning ; terminating, it is true, in 

 one place, but continuing to rage with violence in another. But to infer 

 that they could not, by any possibility, come to an end, if they are really gen- 

 erated in this way, is illogical ; for there may be many causes tending to di- 

 minish and finally destroy their force. 



The quantity of rain which comes down from a great height has a tendency, 

 both by impulse and its cooling effect on the air below, to diminish and some- 

 times stop its upward motion, and in the case of the rains in Jamaica, in the 

 middle of the day ; they appear to invert the motion, and produce a land breeze 

 towards evening. And when the land breeze commences, the air over the 

 middle of the island must come downwards, and then not only will the rain 

 cease, but the cloud which was formed by the upward motion will disappear, 

 as it comes under greater pressure as is demonstrated by experiment. 

 Other means of terminating storms were explained at the latter end of the 

 section on meteoric rivers. 

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