458 Dr. Werner Siemens on the Conservation 



the neutral equilibrium and the adiabatic temperature of the 

 strata at different heights of the atmosphere can be influenced 

 only by the currents of air which are caused by the various 

 heating of the air by the sun's rays and by the various cooling of 

 the same by radiation. The heating of the air, and especially of 

 the lower strata, is by far the greatest in the equatorial zone, 

 and from there decreases approximately as the cosine of the 

 latitude. Consequently, the transformation of solar energy 

 into the kinetic energy of air in motion must be greatest at the 

 equator, and decrease towards the poles. This transforma- 

 tion takes place in the ascending current. If, moreover, we 

 disregard, for the present, the displacement of the hot zone, 

 due to the change of seasons, we have present the conditions 

 for a universal and continuous up-current of air. In fact, we 

 have in the lower trade-winds a continuous flow of air from 

 regions near the pole towards the equator. This current of 

 air must have here a smaller velocity of rotation than the 

 earth's surface situated under it, and must therefore have the 

 direction from east to west, for the reason already mentioned, 

 of the maintenance of the mean velocity of rotation of the 

 atmosphere. 



Since the northern and southern components of the two 

 lower trade-currents, regarded as of equal strength, as they 

 approach the equator rise from opposite sides, their vis viva 

 increases the upward drift of the air. There must therefore 

 take place an upward motion of the whole mass of air of the 

 hot zone in spirals of opposite direction to the rotation of the 

 earth. Only over the equator itself will there be left a ring 

 of air which cannot take part in this upward motion, and 

 whose northern and southern surfaces are grazed by the 

 spirally-rising trade-winds. These, carrying with them the 

 surface-layers of the relatively quiescent equatorial mass of 

 air, must produce in it vortices which communicate to the 

 centre of this mass of air an opposite velocity thus opposed 

 to the rotation of the earth. This is the region of calms. The 

 portions of the trade-winds lying next to the earth's surface, 

 and thus more strongly heated, unite above the wedge-shaped 

 ring of calms and form the central portion of the great equa- 

 torial upward-current. The velocity with which these masses 

 of air ascend must increase in proportion with the rarefaction 

 of the air brought about by decrease in pressure ; since equal 

 masses of air must pass through every horizontal section in 

 unit time, and the vis viva thus obtained must drive the cur- 

 rent high above the upper surface of the atmosphere until 

 its weight, no longer balanced by the pressure of the sur- 

 rounding strata of air, has destroyed the vertical component 

 of its velocity. Hence we have formed above the centre of 



