SCIENTIFIC BALLOON ASCENSIONS VON BEZOLD 



321 



We obtain a good idea of the magnitude of the error due to this 

 'simplification by means of fig. 48, in whose construction only the 

 values up to 4000 meters could be utilized. We see that the corre- 

 sponding curves end at different ordinates since the same altitudes 

 correspond to 'smaller values of the atmospheric pressure when 

 temperatures are low but to higher pressures when the tempera- 

 tures are high. 



In a perfectly similar way to that by which we have just given the 

 quantity of water we compute in the following table 5 the differ- 

 ences of the quantities of heat that are contained, on the average of 

 the respective seasons, in the several sections of the column of air 

 resting on one-square meter of ground. 



w 



K 



jS 



5OO0TK 



4O0OTTI 



30OOTTV 



2000m 



lOOOm, 



Ottl 



FIG. 49 



Of course in this summary the tens have but little significance, 

 exactly as in the above-mentioned table, where the second decimal 

 figure is a pure result of computation, and is retained only for the 

 sake of an easier check. 



Before I come to the table itself I must first explain the word 

 "Thermal-content" or "Warme gehalt" used in the title of this table. 



By "Thermal-content" I understand the quantity of heat that 

 must be communicated to a given quantity of air to bring it under 

 constant pressure from any arbitrary initial temperature up to 

 any given final temperature. The same expression was, as is well 

 known, some time since applied by H. v. Helmholtz to this concep- 

 tion for which, with his approval, I afterward ' substituted the term 

 "potential temperature." Since, however, this last term has mean- 



