458 SHORT MEMOIRS ON METEOROLOGICAL SUBJECTS. 



the air grows heavier, and gradually (in the nortberu hemisphere) breaks 

 its way toward the north, alongside of the cold currents of air which 

 move toward the equator. On account of the force of the earth's rota- 

 tion, the equatorial current of air thus appears as a southwesterly wind, 

 while the polar current of air appears as a northeasterly wind in the 

 northern hemisphere; and thus we see both of these currents are deflected 

 by the force of the earth's rotation, as is the case with the currents of 

 the sea. On both sides of any equatorial current there naturally runs a 

 polar current of air in a southerly direction, and on both sides of every 

 polar current in like manner an equatorial current in a northeasterly 

 direction, and so on round the entire globe. 



If we now direct our thoughts to two of these neighboring currents, 

 which move side by side in diametrically opposite directions, and if we 

 suppose that the polar current moves upon the west side of the equa- 

 torial air-current which is under consideration, it is evident, from what 

 I have elsewhere i)reviously shown in relation to the Gulf Stream and 

 the polar current which runs west of it, that both the currents of air in 

 question are constantly tending to separate from each other. Since they 

 do not separate, however, the consequence is that while this tendency 

 exists, a rarefaction of the air takes place between the two currents, and 

 in consequence thereof the pressure of the air diminishes toward the 

 dividing surface between these currents, whereby, at every point of the 

 currents referred to, precisely that reaction is caused which is required 

 for the preservation of equilibrium with the force of rotation. From the 

 dividing surface between the aforesaid currents of air, the atmospheric 

 pressure must therefore increase toward both sides, if the currents are 

 to continue their course in their diametrically opposite directions, and 

 the increase of pressure in air-currents for any transverse distance I from 

 the dividing surface can, if it is measured by a column of air = h, be 

 computed according to a formula previously given, as applicable to 

 ocean currents, viz : * 



7i sin ^siu^ w . v ,_, 



^1= 13750 > ("^ 



iu which V denotes the velocity of the air-current at the latitude 0, and w 

 the angle w^hich the direction of the current) forms with the east point 

 of the circle of latitude, — the whole in accordance with the formula (70) 

 in my dissertation upon marine currents.! What has been stated shows 

 that the atmospheric pressure iu these currents, when they are of the 

 same density, must diminish toward the common dividing surface of the 



* Note by the Translator. — This formula should have heea 



5f--=2ji vsin (j), 



as has been })ointed out by Ferrel and Hann. Colding's error resulted from having 

 considered but a portion of the eliect of the earth's rotation — an error that also pervades 

 his elaborate memoir on ocean currents. See Ferrel in "Nature," 1871, iv, p. 226, and 

 1872, V, p. 384. 

 t[An abstract of this memoir is given in ''Nature," vol. v, p. 71 et seq.—C A.] 



