PRODUCTIVENESS OF FOG PRECIPITATION 
upper being a thin film of paraffin oil placed 
above a base of heavier castor oil. The finding 
was immediately recorded by microphotography. 
The samples were taken under various fog situ- 
ations, without any consideration of the de- 
posited amount. Altogether 25 tests were evalu- 
ated, each consisted of an average of 12 samples 
with each several hundred or thousand droplets. 
Types of droplet spectrum—tThe derived fre- 
quency distributions of droplet diameters can 
115 
be classified according to the types of droplet 
spectrum, as seen in Figure 4. Each of these types 
presents obvious relations to the existing air mass 
and through it to the productiveness of fog pre- 
cipitation. Polar cold air is characterized by 
dominating small diameters (Types a and b), 
in case of maritime origin, Type a with a range 
up to 10 to 12 » and a remarkable part of diame- 
ters smaller than 2 »; in case of continental origin 
Type b from 2 to 15 w with a maximum number 
Fic. 5—Microphotographic record of cloud droplets from polar cold air; 
small amount of fog precipitation 
