SCIENTIFIC BALLOON ASCENSIONS VON BEZOLD 2QI 



advantage that the adiabats of dry air appear almost exactly as 

 straight lines inclined to the axes at an angle of 45 . On the other 

 hand we must not forget that by this choice of coordinates it is 

 only the temperature that is represented in its dependence on the 

 altitude and hot the thermodynamic condition properly so called, 

 to whose determination a knowledge of the pressure or the specific 

 volume is also necessary. 



But whatever method of presentation we may choose they all 

 have this one point in common, i. e., that each condition charac- 

 terized by the corresponding variables corresponds to a point on 

 the coordinate plane. If now we imagine a given quantity of air 

 (the unit of mass is best) passing successively through different con- 

 ditions then the points corresponding to these conditions arrange 

 themselves in a connected series and form a continuous curve. 



In this way we obtain "curves of change of condition," e. g., as 

 above, "curves of temperature change." 



Since in this study one must know in what direction the changes of 

 condition follow each other, it is therefore necessary to indicate this 

 by an arrow along the curve. If, for instance, the changes follow 

 the altitude, then the arrow shows whether we have to do with an 

 ascending or descending current. 



But we may just as well apply these graphic methods to repre- 

 sent the condition prevailing at a given moment, or the aver- 

 age of a longer interval, along any given line. If, for instance, 

 we plot as ordinates the altitude and as abscissa the temperature 

 prevailing throughout a vertical column of air at a definite moment 

 of time, then the curve becomes a representation of the distribution 

 of temperature prevailing at this moment, or if we add similar 

 curves for the moisture and the pressure it becomes a plot of the 

 total thermal condition along the given vertical. 



In this case I call these "curves of condition" as opposed to the 

 above-mentioned "curves of change of condition," or if we con- 

 sider only the temperature they become "curves of temperature" 

 instead of ' curves of change of temperature." Since the curves 

 of condition do not relate to conditions that follow each other 

 consecutively but that prevail simultaneously, therefore of course 

 no arrow is needed. 



I do not know that any one has yet dwelt on the sharp difference 

 between these two kinds of curves, although both kinds have 

 been made use of. Thus, for instance, the curve for the dependence 

 of the mean temperature on the altitude given on p. 90 in the well- 

 known Lehrbuch of Sprung and constructed from Glaisher's obser- 



