460 Dr. Werner Siemens on the Conservation 



directed current, into the lower equatorial current must take 

 place. The partial change of the upper current into the 

 lower one will take place by means of the tract of horizontal 

 cyclones separating the two regions without any important 

 loss of vis viva. If there were no earth-rotation, this return- 

 flow would take place up to the poles without disturbance. 

 The loss of vis viva by internal friction can only be small in 

 the higher strata of air, on account of their great dimensions. 

 They will therefore flow into the polar regions from all sides 

 with little loss of velocity, there produce a blockade and sink to 

 the earth's surface, in order to return to the equator as a polar 

 current. This process would take place partially in all lati- 

 tudes, and the final result would be a system of cyclones 

 taking place in meridional planes, embracing the whole 

 atmosphere, in which the vis viva obtained by the impulse in 

 lower latitudes is again destroyed by friction with the earth's 

 surface and by internal friction communicating the same to 

 the higher strata of air, or is converted into heat. 



This representation of the circulation is, however, essentially 

 altered by the rotation of the earth. 



In consequence of the continual transference of air from 

 lower latitudes to higher ones, and conversely, the atmosphere 

 must assume a mean velocity of rotation, so that the kinetic 

 energy accumulated in the whole rotation may remain un- 

 altered. As already shown, this mean velocity of rotation cor- 

 responds to that of the 35th degree of latitude. Consequently, 

 the courses of all air-currents must be displaced. Between the 

 35th degrees of north and south latitude, both the upper and 

 under currents will lag behind the earth, and thus acquire a 

 westerly direction ; whilst between the 35th degrees and the 

 poles a velocity increasing rapidly with the latitude, over- 

 taking the earth's rotation, and thus eastward, must prevail 

 in both currents. The return of the upper pole-directed 

 current to the equator takes place therefore below the 35th 

 degree in westerly paths as strengthening of the lower trade- 

 wind, and the cyclonic motions separating the upper from the 

 under current must also assume this figure of motion. 



The motions of the air beyond the 35th degree assume a 

 more complicated form ; whilst the upper air-current, here 

 wholly directed to the pole, will retain its eastward velocity 

 of about 380 m. almost without alteration — since the re- 

 tardation of the same by internal friction can only be very 

 small in the higher regions of the air — the returning lower 

 current will be very considerably retarded by friction with 

 the earth's surface, and the more so the longer this lower 

 course is, 



