84 Progressive Changes of Matter. [Feb., 



in a clear day, than a level surface. This fact is tested in the 

 experience of animal and vegetable existences. The heat of the 

 noon-day sun also proves this fact; hence a variation in the incli- 

 nation of surface will cause also a variation of warmth produced 

 in those places. We are nov/ to consider the uneven surface of the 

 earth, in which we behold hill and dale, the river valley with its 

 varied sides of slope and gorge — the upland range and the moun- 

 tainous country, each presenting some surface form peculiar to 

 itself There is another condition of surface Avhich will vary the 

 amount of warmth produced by the sun's rays. We have spread 

 out before us the forest and cultivated field, the water surface — 

 snows lingering upon the hills or in the shade of the wilderness. 

 Again we behold the shadow of clouds, the passage of storms, 

 and the alternation of a wet and dry surface: add to these the 

 succession of day and night, in which these warming rays fall 

 upon a given surface at unequal angles during every hour in the 

 day. Again, we have a more magnificent order of causes, giving 

 us a still greater variation of temperature in the same localities. 

 The sun, as he comes peering over these northern climes, dispen- 

 ses to us the summer's heat, and receding to the southern extreme 

 of his pathway leaves us to the rigors of the polar blast: hence 

 from this movement of the sun, the general heat is daily increased 

 in one zone, while in an equal ratio it is diminished in another. 

 In a nicely balanced scale beam, how interesting it is, to see it 

 rocked by the weight of the minutest hair. But in the subject 

 before us, the balance beam rests its central point upon the most 

 subtle of all fluids, the atmosphere; — then how inconceivable 

 slight may be the weight to set it in motion. Under the above 

 law and the varied and magnificent causes existing at all times 

 in some form or other, in relation to the production of atmo- 

 spheric currents, what are the effects we calculate will follow. 

 A perpetual circulation of currents in the great body of the 

 atmosphere. The air, unless confined, never appears at rest — we 

 have the soft breath of the morning, the noon-tide breeze, and 

 the sweeping tornado, all perhaps during the same day. Atmos- 

 pheric currents are most commonly indicated by the motion of 

 clouds and vapors, by the waving of trees and fields of grain, 

 by the smoke of fires and by various other phenomena. We have 

 local winds, such as arise around mountains or some prominent 

 head land, or such as trail over the plain without following any 

 settled direction. 



There is another order of winds, generally named from the 

 four cardinal points of the compass;, these may be termed periodic 

 winds. These winds however, are frequently guided by moun- 

 tainous ranges. The southerly wind at Albany, becomes an 

 easterly Avind as it passes up the valley or the Mohawk. A 



