476 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 51 



Thus for expansion from 30 and 76o mm upward and with 10 

 grams as a mixing ratio, we find the saturation point at the inter- 

 section of the dry stage adiabat with the 10 gram line, which occurs 

 at ii° C. and 6io mm pressure. 



Any further expansion must now follow along the adiabat of the 

 condensation stage which reaches the freezing point at a pressure 

 of 465 mra and attains a temperature of — 20 C. at 35o mm . 



The intersection of the condensation adiabat with the gram line 

 will therefore show at any moment how many grams of aqueous vapor 

 are still present, for instance, 3 grams at — 13 C. Since the origi- 

 nal quantity of moisture was 10 grams therefore 7 grams have been 

 condensed either to water or snow. At o° C. we find 6 grams of 

 aqueous vapor remaining, therefore 4 grams have been condensed 

 to water, which would now at once freeze if it were to remain float- 

 ing in the air. 



For the mixing ratio of 3 grams and for initial condition of 20 

 and 76o mm the point of saturation is at — 7 C. and 545 mm which is 

 the intersection of this dry adiabat with the 3-gram line; 



The adiabats of the dry stage become straight lines if instead of 

 the coordinates p and t we introduce log p and log t as the variables 

 putting log p = X and log T = Y so that X — mY = constant 

 which is the equation of a straight line. 



Hertz used this principle in the construction of his table, 22 in 

 which along the horizontal line the values of log p are set off and 

 along the vertical line the values log t. The numbers themselves 

 are written along side as indices. This usage has materially facili- 

 tated the construction of the table. It is only necessary to know 

 any two points of an adiabat in order to draw not only this one but 

 all the others that run parallel to it and are distant from it only by 

 the differences of the constants. 



The value of the constant corresponds to 



dQ 

 T 



which expression is called "entropy" by Clausius and " Warmege- 

 wicht" by Zeuner. 



In the condensation stage we have the formula 



p', t 



log p' — — — m log T — constant = I — — 



Po'< To 



22 Hertz: Graphische Methode usw. Met. Zeit., 1884, S. 426. See previous 

 collection of translations, 1 891, p. 210. C. A. 



I 



