254 Professor Kaemtz on the more important 



It is these two winds, which, engaged in anveverlasting con- 

 flict, produce the phenomena of the winds, and with these the 

 changes in the weather of the temperate zone and of higher la- 

 titudes. Sometimes the one and sometimes the other prevails ; 

 and at other times the two form directly opposing currents, 

 and, at the place where they meet, calms alternate with violent 

 gusts of wind. Most frequently, however, both advance next 

 each other with greater or less violence ; and as in the middle 

 of their course we meet with both winds in greater purity, there 

 arise, at the place where they proceed next each other, whirl- 

 winds of great extent, which are the causes of all the other 

 winds. Without adducing the proofs offered by Dove, it may 

 be sufficient to offer a short account of the alternation of the 

 winds. Let us suppose that the NE. has the preponderance *at 

 the surface, and that it has either completely pressed back the 

 SW., or driven it to very high regions of the atmosphere ; it thus 

 continues to extend, and, as it comes from places more to the 

 north-east, it gradually becomes changed to an east wind. How- 

 ever, the SW. gradually shews itself in the upper regions, as 

 we may observe by the course of the higher clouds, while the 

 vane indicates NE. or E. By the action of the two winds on 

 each other, the current of air becomes gradually SE. and S., 

 until at last it is SW., which direction, owing to the rotation 

 of the earth, is gradually changed to W. But now, the NE. 

 gradually recommences, and as both contend at the surface, a 

 middle direction is produced by the union of the two, which is 

 moved to N W. and N. as the predominance of the NE. becomes 

 greater, till at length this last alone blows in the atmosphere. 

 Thus, in our part of the globe, this circular change is unceas- 

 ingly going forward, only not with the regularity here supposed, 

 for it may happen that the NE. has already turned the SW. 

 to NW. or N. ; but the SW. now acquires new strength from 

 the equatorial regions, and the wind returns, contrary to rule, 

 back to the W. and SW. 



Moisture of the Atmosphere. — If the relations of wind and tem- 

 perature which have now been considered are themselves worthy 

 of close attention, they become much more important by the in- 

 fluence which they have on the constitution of the sky and the 

 pressure of the air. The amount of vapour which arises from a 

 mass of water is a quantity depending on the temperature. The 



