456 Dr. Werner Siemens on the Conservation 



paratively cooler masses of air. The current of air rising 

 with increasing velocity must therefore retain a positive 

 excess of heat up to the highest rarefaction, the descending 

 stream a negative excess above the adiabatic temperature 

 corresponding to the height. 



4. The energy accumulated in the ascending and descend- 

 ing currents of air can only be destroyed again by being 

 again transformed into heat by internal or external friction, 

 or by local increase of pressure. 



5. The mechanical energy accumulated in the rotation of 

 the atmosphere round the earth's axis must be constant, and 

 in the condition of relative rest must correspond to the 

 velocity of rotation of that part of the earth's surface upon 

 which it rests. Since; in consequence of polar and equatorial 

 currents, a constant change in the geographical position of 

 the air-masses takes place, the velocity of rotation of the 

 whole atmosphere must lag behind the velocity of rotation of 

 the earth's surface in low latitudes, and must gain upon it 

 in higher latitudes. The magnitude of the friction with the 

 earth, which diminishes these differences in velocity, must be 

 as great in equatorial latitudes as in the polar latitudes, in 

 order that the constancy of the mean velocity of rotation of 

 the whole atmosphere may be preserved. The velocity lost 

 by friction influences, therefore, only the local magnitude of 

 the difference in velocity. 



6. At the boundaries of currents of different velocities there 

 takes place a constant mixing of neighbouring portions of 

 air having different velocities. By this process, analogous to 

 friction, there is caused a retardation of the more swiftly 

 moving currents, and an acceleration of the slower ones pro- 

 portional to the difference in velocity. There is thus pro- 

 duced in the boundaries an increase of pressure in the swifter, 

 and a decrease of pressure in the slower, currents of air. 



Of these fundamental statements only the last two require 

 special explanation. 



If we suppose the whole atmosphere in relative rest, and if 

 we neglect its height as small in comparison with the radius 

 of the earth, then its vis viva is 



where K is the sum of the vis viva, q the weight of the air 

 resting on the unit area, T the time of revolution of the earth 

 in seconds, and a the angle of latitude. This gives for the 



