96 A NEW ZEALAND NATURALIST'S CALENDAR. 



large amount of heat is liberated. The result is that the 

 wind, in being forced up the mountain sides, pours out an 

 immense quantity of rain on the West Coast, but reaches 

 the summit of the ranges as warm as it was at the foot, 

 this being due to the latent heat which has been parted 

 with. Coming down the eastern slopes of the mountains 

 it regains as much heat as it lost in consequence of being 

 forced up the other side, and so pours down on the open 

 country as a hot wind. This rise of temperature causes it 

 to expand very considerably, so that what is a quiet mild 

 rain-bearing wind at Hokitika, appears on the Canterbury 

 Plains as a strong hot and parching blast, which shrivels 

 vegetation and makes life generally rather disagreeable. 



The phenomenon is common to many countries of similar 

 conformation. Thus southerly winds from the Mediter- 

 ranean, which cause heavy precipitation on the Italian 

 slopes of the Alps, blow over Sputhern Germany as hot dry 

 scorching winds, exactly as our nor'-westers do. This 

 wind is called the "fohn" in Germany and is very much 

 disliked. 



Though these winds "feel" heavy in Southland we 

 used to notice that they seemed to blow down on us at a 

 considerable angle they are really so expanded by heat as 

 to lower the barometric pressure very considerably over a 

 wide area. Therefore, after they have blown for a few 

 hours they are almost invariably replaced by a colder 

 heavier wind from the south-west. This inrush of cold 

 wind usually lowers the temperature of the warmer air to 

 below its saturation point and brings down a more or less 

 prolonged rainfall. \Ve had a very remarkable example of 

 this only as recently as yesterday, when a warm north- 

 west breeze, hardly felt in Dunedin as a wind at all, 

 dropped the barometer very sharply, and into the area of 

 low pressure so produced there came an inrush of cold 

 southerly wind with a very heavy downpour of rain. Of 

 course such an explanation is only a very partial one, for 

 we know little of the gigantic processes which are con- 

 stantly at work in the atmosphere, but it gives a general 

 idea of one at least of the potent causes of weather change. 



