98 THE MECHANICS OF THE EARTH'S ATMOSPHERE. 



But the required directions for the two boundary lines of the mixture 

 can only exist when this mixture passes upwards between the two 

 masses (1) and (2). Only thus can there be a condition of equilibrium. 



Hence results the important consequence that all newly formed mix- 

 tures of strata that were in equilibrium with each other must rise 

 upwards between the two layers originally present, a process that of 

 course goes on more energetically when precipitations are formed in 

 the ascending masses. 



While the mixed strata are ascending, those parts of the strata on 

 the north and south that have hitherto rested quietly approach each 

 other until they even come in contact, by which motion the difference 

 of their velocities must necessarily increase since the strata lying on 

 the equatorial side acquire greater moment of rotation with smaller 

 radius, while those on the polar side acquire feebler rotation with a 

 larger radius. If this occurs uniformly along an entire parallel of lati- 

 tude we should again obtain a new surface of separation for strata of 

 different rates of rotation whose equatorial side would show stronger 

 west winds than the polar side, which latter might occasionally show 

 east winds. On account of the numerous local disturbances of the 

 great atmospheric currents there will, as a rule, be formed no contin- 

 uous line of separation, but this will be broken into separate pieces 

 which must appear as cyclones. 



But as soon as the total mixed masses have found their equilibrium 

 the surfaces of separation will again begin to form below, and new 

 wave formations will initiate a repetition of the same processes.* 



From these considerations it follows that the locality for the forma- 

 tion of billows between the strata of air is to be sought especially in 

 the lower parts of the atmosphere, while in the upper parts an almost 

 continuous variation through the different values of rotation and tem- 

 perature is to be expected. The boundary surfaces of different strata 

 of air, along which the waves travel, have one edge at the earth's sur- 

 face and there the strata becomes superficial. Experience also teaches, 

 as does the theory, that water-waves that run against a shallow shore 

 break upon it, and even waves which originally run parallel to the 

 shore propagate themselves more slowly in shallow water. Therefore 

 waves that are originally rectilinear and run parallel to the banks will 



* In the last section of my previous paper [see ante p. 91] I located the origin of 

 the discontinuity principally in the upper strata of the atmosphere. But in that 

 paper the point of departure was different from the present. In that the question 

 considered was: If at any time the atmosphere has attained an initial stage of contin- 

 uous steady motion without surfaces of separation, where will such a surface first 

 form ? To this the answer is : At the upper houndary of the tropical belt of calms. 



At present the question is, Where in consequence of processes of mixture will the 

 surfaces of separation necessarily he renewed ? But I must take back the proposi- 

 tion on page 91 that treats of the descent of mixed strata, now that I have found 

 the law expressed in this paragraph. 



