194 THE MECHANICS OF THE EARTH'S ATMOSPHERE. 



Moreover, a is determined by the same equation as before,* 

 Finally, from the equation (9) 



m 



cV 3 =const+#— h 



dz 



there results the following : 



c 2 r 3 =const+f J B 2 1 (jf^+X*) cos 2 0- X i cos 4 6 } 



(17) 



This last equation allows of a direct comparison with the above-men- 

 tioned observations of the distribution of pressure. 



IV. 



The average values of the pressure of the air in the Southern Hemi- 

 sphere are given in the following table (under the column of observa- 

 tions) as a function of the latitude.* 



Air pressure at the earth's surface. 



These pressures are fairly represented by an expression of the form 



p = pz+ a cos 2 6—b cos 4 6. 



If we determine the constants a and b from the observed values for two 

 different polar distances, for which I have used #=50° and #=20°, 



then we obtain 



# = 75S+31.295 cos 2 #-61.094 cos 4 6. 



By the means of this formula the values given in the second column, 

 under " computed," have been obtained. 



*See A. Sprung, Lehrbuch der Meteorologie, p. 193; J. vau Bebber, Handbuch der 

 Witterungskunde, II, p. 136. [These figures are taken originally from Ferrel, •' Meteo- 

 rological Researches," i, 1830.— C. A.] 



