238 



THE ATMOSPHERE AND METEOEOLOGY. 



Still, we must not expect to find exactly the same amplitude per 

 month at all the points situated at the same distance from the equator. 



35 



;30 



25 

 go 

 15 



5 



f I I _, I 



Ifl" 20" 30" AO"* ^09 60* 2J>» 



Fig. 102.— Monthly amount of the oscillations of the barometer in the northern hemisphere. 



In this respect, on the contrary, we observe great diversities, which 

 we must attribute to the difference of continental forms and of 

 climates. By uniting with each other all the points in which the 

 same monthly variation in the pressure of the air occurs, we obtain a 

 series of lines called iso-baromcfric, which all curve to the north across 

 the Atlantic, and on the w^hole much resemble the lines called 

 isothermal* These are curves imagined by Kiimtz, which indicate 

 the true latitude for the general movements of the atmosphere. In 

 spite of the extreme mobility of air, in spite of the tempests which 

 roll with fury from one point to another of the horizon and disturb 

 for a moment the regularity of atmospherical phenomena, these lines 

 maintain from year to year their mean direction ; while indicating 

 the disturbances of the air, they show by their permanence and their 

 regularity how much these commotions depend on the great laws 

 which rule our planet. 



* See below the section entitled. Climates. 



