PAPER BY PROF. BEZOLD. 



271 



Since on the other hand, according to the data recently collected by 

 Hann,* quantities of water considerably greater than these can remain 

 suspended in the air (as mist, fog, and cloud), therefore we see very 

 plainly that, while the formation of cloud can be caused by mixture, 

 yet the precipitation of rain or snow in any appreciable quantity can 

 scarcely be brought about iu this way. 



At the same time the following diagram, uhich we here make use of 

 for graphic computation, enables, iu the most simple manner, to com- 

 pare the quantity of precipitation formed by mixture with that which 

 is produced by direct cooling as well as that produced by adiabatic 

 expansion. 



If we assume that by mixture under a favorable mixing ratio of sat- 

 urated air at the temperature t 2 with other saturated air at the temper- 

 ature t u the quantity of water a is precipitated (see Fig. 42), then we 

 obtain the same quantity of precipita- 

 tion when we directly cool the com- 

 ponent y 2 , from its temperature t 2 to a 

 new temperature t d , for which we have. 

 y' il = y' 2 — a, but y' d is the ordinate 

 whose foot is T d in Fig. 42. 



A glance at the general saturation 

 curve suffices to show at once that the J-J^ 

 difference t 2 — t d is very much smaller 

 than the difference t 2 — t ; that is to say, 

 that a very slight direct cooliug affords 

 as much precipitation as a considerable 

 cooling by mixture with colder air, even 

 when the latter is completely saturated. 



The effect of adiabatic cooliug is seen wheu iu the diagram we draw 

 the adiabatic curve as a function of the temperature and quautity of 

 water contained in a kilogram of moist air. 



Such an adiabatic curve sinks, as we easily perceive, rather more 

 slowly from the right toward the left than the saturation curve. For 

 since in this case the diminution of temperature goes hand iu hand 

 with the increase in volume, therefore, the quantity of moisture neces- 

 sary for saturation will for falling temperatures be greater than it 

 would be if the initial pressure were maintained ; that is to say, than it 

 would be by progressing along the saturation curve. 



The adiabatic (which without any difficulty can be introduced into 

 the diagram with sufficient accuracy with the aid of Hertz's Graphic 

 Method*) will therefore have a path similar to that shown by the curve 

 F 2 A in Fig. 42. 



* Meleorologische Zeitschrift, 1889, vol. VI, pp. 303-306. 



* Meleorologische Zeitschrift, 1884, vol. I, pi. VII. [See No. XIV of this collection of 

 Translations.] 



