PAPER BY PROF. BEZOLD. 



271 



Since on the otlier band, according to the data recently collected by 

 Hanii,* quantities of water considerably greater than these can remaiu 

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

 plainly that, whde 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 in this way. 



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

 for graphic computation, enables, in 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 tz with other saturated air at the temper- 

 ature ^1, 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 2/2, from its temperature t-z to a 

 new temperature t^, for which we have 

 y'jz=y'2 — a, but y'a is the ordinate ,jh. 



whose foot is T^ in Fig. 42. 



A glance at the general saturation 

 curve suffices to show at once that the 'J'7,,^ 

 difference t-i — tj^ is very much smaller 

 than the difference ti — t\ that is to say, 

 that a very slight direct cooling aftbrds 

 as much precipitation as a considerable 

 cooling by mixture with colder air, even 

 when the latter is completely saturated. 



The effect of adiabatic cooling is seen when in the diagram we draw 

 the adiabatic curve as a function of the temperature and quantity 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 t mperature goes hand in 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 

 Ft A in Fig. 42. 



y> 





-^^ 



* Meteovologische Zeitschrift, 1889, vol. vi, pp. 303-.306. 



* Meteorologi.whe Zeitschrift, 1884, vol. i, pi. vii. [See No. XIV of this collection of 

 Translatious.] 



