1847.] Progressive Changes of Matter. 85 



north wind is seldom experienced at Herkimer, while at Albany 

 it is common. The prevailing periodic wind in this latitude, is 

 the north-westerly, and this we should expect to be so from the 

 fact that the greater amount of heat is dispensed along the line 

 of the equation. In the movement of all these winds, there ap- 

 pears to be a general uniformity, varying perhaps more in intensity 

 than otherwise. There is a class of winds which appear to be 

 more continuous than the preceding; such as the trade winds and 

 the monsoons. There is another phenomenon in the theory of 

 winds, interesting to those who may contemplate it. There are 

 at times various currents of air existing, the one above the other, 

 at the same time. Three or four strata of clouds are not unfre- 

 quently seen moving the one over the other, and in as many 

 directions, and so continuing for a day and perhaps days. It may 

 not appear mysterious that these various currents should exist for 

 so long a period, when a cold and a warm current coming in 

 juxta-position, have so strong a propensity to mingle and the 

 barrier intervening so feeble. It is said that there is a great 

 atmospheric current constantly passing over from the equator to 

 the poles. This perhaps would follow from the fact that the ten- 

 dency of surface winds is toward the equator. 



Evaporation, Clouds and Rain. 

 That water disappears on being evaporated is familiar to all, 

 but that it maintains an elementary existence in this condition 

 may not be so well considered. The last visible traces of evapor- 

 ating water is seen in the form of steam and spray, but it soon 

 disappears in the surrounding air. Whether it in its evanescent 

 state combines chemically or mechanically with the atmosphere, is 

 not fully determined, — the matter seems to be somewhat in dispute. 

 A simple experiment of steam will favor the idea that it is me- 

 chanically combined. Attach a tube to the spout of an ordinary 

 tea-kettle, containing boiling water, and keep the exterior surface 

 cool by snow or cold water, and instead of a jet of steam escaping 

 there will be a trickling of water. Let a plate be held over a 

 steam rising from boiling water, and drops will collect on the un- 

 derside. The process of distilling is but the evaporating and 

 condensing water, and is a method resorted to for the purpose of 

 freeing it from its impurities. There are two agents in nature 

 that appear to be active in hastening the process of evaporation, 

 the warmth of the sun's rays and a brisk wind. Manufacturers 

 of cloths have profited by an observance of the latter fact. They 

 construct a fan- wheel w-hich is moved with great velocity; the 

 warp on being sized becomes wet, they pass it over this wheel 

 while in motion, and it is dried by this current of air. Our ex- 

 perience has taught us that the wet surface of the ground after a 



