26 THE EUROPEAN STORM OF DECEMBER 21-28, 1836. 



not coincide with that of the area of low barometer, or Avith the centre of the area 

 of rain and snow. In the United States, on the northeast side of a storm, at a dis- 

 tance of over 500 miles from the area of rain and snow, the thermometer sometimes 

 rises even twenty degrees above its mean height. 



14. The storms of Europe are very much modified, and sometimes in a great 

 measure controlled by the Alps of Switzerland. By the interposition of these 

 mountains the air which sweeps over them is forced up to a great height, where it 

 is suddenly cooled ; its vapor is condensed ; heat is accordingly liberated, by Avhich 

 the surrounding air is expanded, and rises above the usual limit of the atmosphere. 

 It thence floAVS off laterally, leaving a diminished pressure beneath the cloud ; that 

 is, the barometer shows a diminished pressure in the neighborhood of the moun- 

 tain. The mountain thus becomes the centre of a great storm, and the storm may 

 continue stationary for several days, being apparently held in its place by the action 

 of the mountain. 



