196 THE MECHANICS OF THE EARTH'S ATMOSPHERE. 



valt:e of tbe rotatory niotiou is positive, that is to say, directed toward 

 the east ; tbeuce to tbe equator tbe value is negative, therefore directed 

 toward tbe west. 



Tbese results cnu easily be combined with tbe conclusions of my pre- 

 vious memoir, accordiij<^- to which tbe motion of ro ation can be consid- 

 ered as the sum of two terms that are of entirely different natures. Of 

 the second term It was remarked especially that the current correspond- 

 ing to it tirst attains sensible values at great altitudes. This therefore 

 becomes at that altitude materially larger than tbe above deduced av- 

 erage value. The first term gave a movement entirely confined to the 

 lower strata of the atmosphere: it is directed towaid the east from the 

 pole down to 35'^ latitude, but directed toward the west exclasively in 

 tbe equatorial zone and less in velocity than the first com])onent move- 

 ment. The numerical computation leads to tbe same conclusion, since 

 j2 i-^ small in com]>aiison with Xi Since from 35° of latitude down to 

 tbe neighborhood of tbe equator there are two currents of 0])posite 

 signs flowing over each other, therefore the place where tbe average 

 movement of rotation is 0° will lie nearer to tbe equator than to 35°. 



Therefore the conclasion of W. Siemens, which gave tbe tirst stimu- 

 lus to the present investigation, has to be subjected to a modification 

 only in so far as we must consider that the westward movement of the 

 upperregionsand higher latitudes has a predominance over the easterly 

 movement of tbe lower regions and lower latitudes, because the former 

 loses a much smaller fraction than tbe latter of its living force in con- 

 sequence of friction. 



The vertical and meridional components V and iV'are to be added to 

 the corresponding components that were computed in my first memoir. 

 The vertical comjionent is positive at tbe equator and at the i)ole, it 

 therefore gives an ascending current at both places, whereas Fis neg- 

 ative throughout a broad central zone. Therefore at the equator the 

 ascending current is strengthened, at the pole the descending current is 

 enfeebled. 



The meridional component iV is zero at tbe surface of the earth at tbe 

 equator ; it is negative, i. e., it is directed toward the south from thence 

 to about 24° latitude ; thence to the pole, where it is again zero, it has a 

 northerly direction. Therefore in the tro])ics it strengthens tbe equa- 

 torial current and in higher latitudes it enfeebles it. Perhaps this ex- 

 plains the occurrence of northwest winds which frequently occur in the 

 southern hemisphere between 50° and 00° south latitude. 



Finally it may be remarked that tbe formula abo\'e used for the dis- 

 tribution of pressure agrees stdl better with tbe observations if a third 

 term with a Gth power of cos 6 is introduced. This term would also 

 find its explanation by the analytical devel()})ment, since the newly 

 found meridional current should ]iroi)erly be again evaluated, in order 

 to further compute the movemeutG of rotation that are to be added 



