Chemical and Physical Notes 



119 



TABLE XX. Temperature of the air at St Moritz, observed at 

 Intervals of twenty seconds. 



There is a class of weather which is generally known by its Alpine name 

 Fohn, the distinguishing feature of which is the rapidity with which the 

 temperature of the air changes from moment to moment, and the excep- 

 tionally high average temperature of the air. 



" It has been most observed in the valleys stretching in a northerly 

 direction from the main summit line of the chain of the Alps and takes 

 the form of an abnormally warm wind blowing from the mountains 

 towards the plain. It has largely occupied the attention of continental 

 meteorologists, and more particularly it has been the subject of exhaustive 

 investigations by Hann, who has shown by very strong evidence that its 

 high temperature must be due to its compression in descending from 

 a great altitude. In the descriptions of the Fohn, attention is almost 

 exclusively directed to the high average temperature of the air, and no 

 mention is made of its extraordinary variations, although every observer 

 must have noticed them. They are so great as to be recognised at once 



