116 
wire screen. Did you make any estimates of how 
much the precipitation is increased by fog drip 
in a normal forest in a location similar to yours? 
Dr. Grunow—In order to test the effective 
deposit on natural obstacles we have made meas- 
urements with a normal rain gage and with tubs 
under trees which acted as a natural fog meter, 
and in an open area with the fog gage, all at the 
same time. In case of fog without rain we found a 
reduction factor of 0.5 to 0.8 within the forests 
and of 3.2 on the edge of a forest. The reduction 
factors thus found depend on kind, form, and 
size of the trees and of the density of the woods. 
Therefore the reduction factor is only correct for 
the place at which these measurements are made. 
Dr. H. Weickmann—You had pine trees? 
Dr. Grunow—Yes. 
Dr. Weickmann—They would have a higher 
collection efficiency than trees with leaves. 
Dr. Grunow—The pine trees stand before our 
door. It is true, conifers have a higher efficiency 
than broad leafs, but more important is the 
situation of a forest in relation to the fog-bear- 
ing current of air. The highest amounts will be 
caught at the edge of the woods, but also within 
the forests a deposit of fog takes place. I re- 
member, too, the work of Hori in Japan. He has 
also found considerable amounts within a forest. 
Dr. W. E. Howell—With reference to your 
first paper, I recall that some time ago, C. K. 
Stidd (Cube-root-normal precipitation distribu- 
tions, Trans. Amer. Geophys. Union, 34, 31-35, 
1953), when he was considering a possible repre- 
sentation of frequency distribution of rainfall 
amounts found zero, limited at dry stations for 
weekly or monthly rainfall amounts. Apparently 
there is a straight line relationship of the cube 
root of the fall amount broken down for very 
small amounts, and I presumed this was due to 
the fact that amounts less than one millimeter or 
at some stations less than one hundredth of an 
inch were not properly recorded. It occurs to 
me to wonder whether the measurement that you 
have made of the minute rainfall amounts would 
verify Stidd’s presumptions that the cube root 
relationship holds down to very close to the zero 
line. I think it might be of interest of investiga- 
tion. 
Dr. Grunow—Thank you for this reference. In 
our further investigations we will investigate this 
relationship. I think this range of minute pre- 
cipitation, although the monthly amount is not 
modified by this with regard to climatological 
DISCUSSION 
and hydrologic applications, is worthy of con- 
sideration with respect both for theoretical and 
practical purposes, especially for agricultural 
meteorology and for artificial stimulation of rain. 
Dr. B. J. Mason—When you are considering 
the collection efficiency of the fog catcher, do you 
regard this in terms of the collection efficiency 
of the individual wires? 
Dr. Grunow—Yes. 
Dr. Mason—When much fog is coming past 
the cylinder, do the pores, the spaces between 
the wires, become filled with water? 
Dr. Grunow—In winter with riming, yes, but 
in summer we have found that is not of sig- 
nificance. This can be deduced from the nearly 
linear relationship between the amount deposited 
and the velocity of the wind. 
Dr. Mason—Nagel in South Africa got rather 
unreasonable results because when he deduced 
the water content of the clouds from the collec- 
tion efficiency of the single wire and the velocity 
of the cloud air which had gone by, he was out by 
a factor of 5 to 10, I think. This may have been 
because the spaces in between the wires were be- 
ing filled. Then it is no longer possible to regard 
the cylinder as a number of individual wires. I 
would not say you should go so far as to regard 
it as a solid cylinder, but it may have approached 
that. 
Dr. Grunow—Nagel assumed a water content 
of approximately 1 g/m’, and this is a very high 
amount. The efficiency of a wire net cylinder is 
higher than that of a solid cylinder, because 
in the latter case, with increasing wind velocity, 
the current lines are more conducted around the 
profile. But the effect is less than the theoretical 
factor because some spaces will be closed by 
water. But, more important, the efficiency factor 
is nearly independent of wind velocity. We can 
observe the behavior of the cylinder in each 
weather situation because we have the instru- 
ments before our door, and we found that at low 
wind velocity there are no more spaces between 
the wires filled with water than at high velocity. 
However, measurements with our fog gage are 
proposed for determination not of the water con- 
tent of clouds but of the additional fog precipita- 
tion, deposited in the same manner as by natural 
hindrances, and for this purpose we can use any 
efficiency factor. 
Mr. Aldaz—At Mt. Washington Observatory 
we do some collection for the Atomic Energy 
Commission. We use a frame with no more than 
