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PAPER BY PROF. I3EZOLD. 241 



Furthermore, the lines whose projections are here considered are not 

 so far from the coordinate plane as in summer, because the absolute 

 capacity for moisture remains always slight. 



If now we follow more accurately the change of condition during 

 ascent in the cyclone, we may at first assume that the process up to the 

 attainment of the upper limit of the 

 cloud stratum very nearly agrees 

 with the adiabatic expansion, since 

 below this limit radiation, either to 

 or from, can only play an unimport- 

 ant part. If however a departure 

 from the adiabatic process does oc- 

 cur then it can be only in the oppo- 

 site direction to that which occurs 

 in summer, that is to say, the lines 

 will descend more decidedly than in 

 summer. 



In Fig. 35 this latter case is as- 

 snmcd, as also that the passage out 



of the dry stage into the snow stage takes place immediately. From 

 this point onwards the curve of condition again sinks more gradually, but 

 with steadily increasing gradient in consequence of the overpowering 

 cooling that certainly occurs at higher altitudes, until finally the turning 

 point is attained and compression takes the place of expansion. The 

 entire course of the change of condition to this point is presented by 

 the curve abc. From this point onwards in consequence of the compres- 

 sion, the curve of condition must gradually advance to the point d. So 

 far as our knowledge of the actual conditions of the atmosphere has at- 

 tained hitherto, this gradual return to the point d occurs in such a way 

 that at greater altitudes the compression proceeds adiabatically accord- 

 ing to the adiabatic of the dry stage, whereas on approaching the ground 

 the cooling by radiation that prevails there causes a deviation of the 

 curve of condition from the adiabatic toward the axis of ordinates, 

 and corresponding thereto the curve shows a course like cd. This curve 

 however is nothing but the graphic expression for the well-known in- 

 version that occurs on clear winter days in the vertical distribution of 

 temperature. By reason of this inversion the curve near d approaches 

 the dew-point curve, aud can even pass it, so that condensation must 

 occur and in the form of ground fog. But with the begiuning of the 

 formation of fog the radiation increases materially and corresponding 

 to it the temperature diminution becomes always more intense with the 

 proximity to the earth of the descending current of air. 



Whether the passage from c to d be also possible by some other path 



by which from the very beginning of the compression the cooling and 



therewith the departure of the curve from the adiabatic makes itself 



felt, is a question that can be decided only after an accurate test com- 



80 A 1C 



