INFLUENCE OF PREVAILING WINDS. 83 



considered wind entitled to a leading place in this 

 respect, because rains and other changes of weather 

 are mostly brought about by variations of wind, pro- 

 ducing sudden alterations of temperature. 



Thus rain, as we know, is caused by a warm current 

 of air, surcharged with watery vapour, meeting a cold 

 one, which condenses and precipitates its superabundant 

 moisture as rain. 



In a changeable climate like England, therefore, the 

 influence of the winds is peculiarly marked, and those 

 who aspire to become weatherwise there will find 

 noting the variations of the wind, by means of a vane 

 placed in some commanding position, one of the best 

 aids in making forecasts as to w^eather. The cause of 

 our rainy climate, for instance, becomes apparent when 

 we observe that the prevailing wind is from the S.W., 

 and that this wind comes to us across a vast expanse 

 of ocean, from warmer latitudes, and therefore sur- 

 charged with vapour, which is precipitated on meeting 

 with our variable and colder winds. 



We have, however, placed heat (i.e. temperature) and 

 elevation, which, as we have explained, modifies tem- 

 perature in certain well-known mathematical ratios, 

 before wind, as the two leading factors of climate, 

 because it is now pretty well a matter of ascertained 

 fact that wind is simply a product of heat, and that 

 the sun which is the ultimate source of every form of 

 life and movement, and in the widest and most literal 

 sense of the term, governs everything here on earth, 

 among other things, creates the wind. 



" From the heat of the sun," says Professor Tyndall,* 



* Heat a Mode of Motion, by Professor John Tyndall, F.R.S., 1875, 

 p. 164. 



