SCIENTIFIC BALLOON ASCENSIONS VON BEZOLD 289 



Helmholtz and had been rather thoroughly developed by W. M. 

 Davis, but that differed often and sometimes to an important extent 

 from the views generally adopted. 



The Results of Balloon Voyages published in the present work 1 

 (whose complete reductions by A. Berson and R. Suring have been 

 accessible to me only within a very short time) allow us to check 

 by experience the theoretical conclusions given in the above-men- 

 tioned memoir of May 1898, and to show to what extent they need 

 to be corrected and supplemented. 



Since it is remarkably difficult to perceive the full significance of 

 the formulas that represent the thermodynamic changes of ascend- 

 ing and descending currents, therefore it is helpful to present them 

 graphically. 



The first to apply a graphic method to these problems was H. 

 Hertz. But the diagram prepared by him had for its object only 

 the replacing of numerical computation by a simpler, less laborious 

 operation. Some years afterward I attempted to follow the 

 processes themselves as such by means of appropriate diagrams. 



Since in the present work an extensive use will be made of this 

 method in order to present the condition of the strata of air through 

 which the balloon passes, it seems appropriate to say a few words 

 relative to these diagrams in general. 



In designing such diagrams one may have in mind many points 

 of view. If, for instance, we deal only with purely theoretical 

 investigations then it is most appropriate to consider only the fact 

 that the condition of a given quantity of atmospheric air is com- 

 pletely determined when we know the pressure, the temperature, 

 and the quantity and form of its moisture. This last item is 

 necessary because particles of water or ice so long as they float in 

 the air are to be counted as constituents of the atmosphere. 



Since the above-mentioned data determine also the volume occu- 

 pied by the unit mass of atmosphere or the so-called specific volume, 

 therefore this latter quantity may be adopted as the independent 

 variable instead of either one of the others, and we may characterize 

 the condition of the atmosphere by the pressure, specific volume 

 and water-content. Hence in the graphic presentation, we choose 

 pressure and volume as the coordinates as has long been customary 

 in the mechanical theory of heat. 



This method which I have hitherto used exclusively offers the 

 great advantage that for any given change of condition we can take 



1 Wissenschaftlicbe Luftfahrten, 3 volumes. Berlin. 1900. 



