104 On Dove's Laio of the 



these two currents form the skeleton of the whole complex 

 phenomena within the ec-tropical region, the principal 

 features of which we have to explain for the southern hemi- 

 sphere.* Throughout the remainder of my paper, therefore, I 

 will refer to the phenomena as they present themselves in our 

 hemisphere. 



Up to the present time we have supposed the earth not to 

 he in a state of rotation, and we found two currents in the 

 southern hemisphere, the one from the equator at a great 

 height above the equatorial belt of calms, and then descending 

 to the earth's surface, moving towards the pole; and the 

 second in a northern direction flowing from the pole towards 

 the equator. But the rotation of our earth alters this state 

 of things considerably, as we at once perceive, when entering 

 into Hadley's theory of the cause of the " trade winds." 



Columns of air proceeding from the poles in an originally 

 northern direction will have a smaller rate of motion, in the 

 sense of the rotation of our earth, than the parallel of lati- 

 tude at which they arrive, f and an observer on that parallel 

 participating in the rotation of the earth from W. to E., 

 will find a resistance offered him by the comparatively 

 stationary columns, which cannot follow at once at the same 

 rate, and the result will be that the south direction will be 

 changed into one between east and south. 



Further, we find with regard to the columns of air moving 

 from the equator to the pole that they will have a greater rate 

 of motion, in the sense of the rotation of our earth, than the 

 parallel of latitude at which they arrive, and an observer on 

 that parallel will consequently feel a draft of air from the 

 west, the northern direction of the current thus being altered 

 into one between N. and W. It is the usual practice to call 

 the S.E. current the "polar current" and that flowing from 

 the N.W. direction the " equatorial current." The greater 

 the difference of the rate of motion, in the sense of the rota- 

 tion of our earth, between the place of observation and the 

 column of air, the greater will be the deflection of the " equa- 

 torial current" towards W., and of the "polar current" 

 towards E., under the supposition that the rate of meridianal 

 motion of the column remains constant. Those parts of the 

 column of air which arrive later at a place of observation 



* I give these few explanations because the different recently pub- 

 lished works have partly introduced confused ideas on this subject. 



t As the motion is in a ratio of the radius of the parallel. 



