20 



A. BL YTT. 



[No. 8. 



atmosphere should, thus, become imeven, and, consequently, in 

 the upper strata of the atmosphere air must flow from the warm 

 regions into the cold ones, so that equilibrium be maintained. 

 For this reason a greater mass of air will lie over cold regions, 

 which have therefore a higher atmospheric pressure. But at 

 the surface of the earth, too, the equilibrium will be disturbed 

 as a high atmospheric pressure will drive the air from the cold 

 to the warm regions. As long as the temperature of the air 

 varies, movements will be created by the disturbed equilibrium, 

 during which, therefore, air will flow from the cold to the warm 

 regions along the surface of the earth and vice versa in the 

 upper part of the atmosphere. In winter as well as in summer 

 the disturbances of the equilibrium of the atmosphere will pro- 

 ceed from the continents, because the latter are heated and 

 cooled more intensely than the oceans. Over the ice covered 

 interior of Greenland the sun in the summer cannot create any 

 low pressure because all its heat is consumed in melting the 

 snow. Even in the summer comparatively cold air and high 

 pressure prevails over Greenland, and this is probably the cause 

 of the atmosphere in the North Atlantic differiug from the above 

 mentioned la w, inasmuch that this ocean has a low pressure even 

 in summer. This low pressure, which lies generally near Ice- 

 land, is, however, more marked in winter. 



The air, according to the law of Buys Ballot, moves against 

 the low pressure, so that in the Northern Hemisphere one has 

 the low pressure a little in front, to the left, when turning the 

 back to the wind. That is a but natural consequence of the 

 rotation of the earths axis. At lower latitudes this action is 

 more intense. Air, flowing from lower to higher latitudes, retains 

 for a time its original speed of rotation, and will thereby deviate 

 in the direction of the rotation of the earths axis i. e. to w ards 

 the east. And vice versa, when the air flows from higher to 

 lower latitudes. In this manner southerly winds become south- 

 westley, and northerly ones north-easterley. In fact, the low 

 atmospheric pressure at Iceland draws the south-west winds up 

 the North-Atlantic, and as the cause prevails all the year round 



