SHORT MEMOIRS ON METEOROLOGICAL SUBJECTS. 431 



The earth's rotation will exert its influence upon this current of air; and 

 under the simultaneous influence of gravitation and the deviation to the 

 right in consequence of the rotation, the level surfaces, or surfaces of 

 equal pressure, can no longer remain parallel to the earth's surface, but 

 must ascend toward the southeast. 

 If we designate by 



n the angular velocity per second of the rotation of the earth, 



2r 

 ~ 8G16.4 ' 

 <P, the geographical latitude; then will 

 n sin <p = the deviation to the right, or the apparent turning which a 

 moving particle experiences, as is shown in elementary 

 physics ; 

 V n sin ^ will therefore be the linear deviation where 



V is the path described in the unit of time, and consequently 

 2vnsm</' is the corresponding acceleration [Beschleimiguiig]. 

 If we designate by 



h the ascent of the level surfaces for a breadth h of the current 



of air, and by 

 g the acceleration [Beschleunigung] due to gravitation, the fol- 

 lowing equation must then obtain : 



g • Y = 2vnsiu <p , 



or 



, 2hvn&ma> 



h = ' 



g 



From this equation (which has already been previously applied to the 

 computation of the elevation of the water on the right bank of our rivers 

 in conwsequence of the earth's rotation, and which must also hold good 

 for currents of air) can be computed the ascent from northwest to south- 

 east of the level surfaces in our current of air. If we take for <f its mean 

 value 530, and for b 1113 kilometers, we find. 



h = 39G.5 meters. 



Therefore the surfaces of equal pressure are elevated by 396 meters 

 from northwest to southeast, which corresponds to a difference of press- 

 ure of 37.7 millimeters of mercury. In our present case, therefore, 

 simply in consequence of the influence of the earth's rotation upon the 

 southwest wind, the pressure must diminish by 38 millimeters from the 

 northern slope of the Alps to the northern portion of Scotland. I 

 see no way by which we can evade this conclusion. Owing to the rota- 

 tion of the earth, a current of air must always, in the northern hemisphere, he 

 accompanied by a diminution of pressure on its left side. But this diminu- 

 tion of pressure corresponds to a condition of equilibrium so long as the 

 movement of the air, or the quantity v, remains the same. There are, 

 therefore, barometric depressions (and so-called barometric gradients), 

 and very large ones too, that are the consequences of air currents whicli 



