HUTCHISON'S OBJECTIONS, WITH REPLIES. 467 



supplied from underneath, by aerial currents near the sur- 

 face of the ground, are constantly and simultaneously oc- 

 curring on an immense number of different parts of the 

 earth's surface. Whirlwinds afford examples of upward 

 vortices of small extent. Sea and land breezes, monsoons, 

 and local as well as more extended winds, blowing from a 

 cold towards a comparatively warm climate or locality, can 

 only be accounted for by supposing that opposite aerial cur- 

 rents simultaneously exist in the upper and lower halves of 

 the atmosphere. The air, in such circumstances, must be 

 gradually descending over the cold locality to supply the 

 lower current, and ascending over the warm locality to sup- 

 ply the upper current. But some of the facts which I have 

 mentioned, such as the case of the north wind in Egypt, sea 

 and land breezes in intertropical climates during the dry 

 season, and the general fact of all winds that blow from a 

 cold towards a warmer locality, being comparatively dry 

 winds, show that the upward ascension of air is not the 

 only cause of rain. 1 And judging from the facts mentioned, 



mystery how so great a quantity of vapor is condensed by cold, in air which 

 is at the same moment receiving such an immense amount of caloric. 



1 This conclusion does not follow from the premises. It would be logical 

 to say, these facts show that an upward motion of the air is not always a cause 

 of rain ; and such is undoubtedly the fact. I have myself seen hundreds of 

 upmoving columns forming large cumuli without producing rain ; but it cer- 

 tainly does not follow from that fact, that cumuli are ever formed without up- 

 moving columns. 



Flat low islands in the West Indies have sea breezes, and of course upmov- 

 ing columns in the central parts of them, but there being no mountains to 

 prevent these columns from being swept off, out of the perpendicular, before 

 they rise high enough to form dense and deep clouds, rain is frequently not 

 the result. Now, when the wind blows from the north west at. Philadelphia, 

 though upmoving columns may be formed in great numbers, as they no doubt 

 are, yet they do not rise very high till they enter a current above, moving in 

 a different direction, and though clouds may begin to be formed before they 

 enter that current, yet, when they do enter it, the columns will be broken and 

 their force destroyed. 



On the contrary, whenever the lower current of the air is moving in the 



