SWISS RANDOMIZED HAIL SUPPRESSION PROJECT 393 
*Sondrio 
+ 
Pre. Grigna 
e 
as Bergamo 
(50) 
e 
(so) Milano Lingte 
vercelli 
(30) 
Piacenza 9) 
($0) 
"parma 
Ghedi 
Q 
e 
(=) Ferrara. 
(50) 
Marina o/ Ravenna 
e = 
Bologna 
(so) 
(50) 
Rimini 
e 
Sasso Feltrio (50) 
Ancona 
(50) 
(50) 
(50) 
Frontone 
S 
e 
Macerata 
Fig. 6—Kolmogorov-Smirnovy test of northern Italy, 1957 and 1958; per- 
centage probability P of an error of the first type 
precipitation, and as chance would have it the 
seeded days were unduly favored. Statistical 
treatment of the observational data, which in 
conclusion we shall now consider, clearly shows 
that this is, in fact, the correct explanation. 
The experimental results with regard to rain- 
fall were evaluated statistically according to the 
test procedure developed by Kolmogorov and 
Smirnoy [Darling, 1957]; the evaluation was 
carried out by P. Schmid, a statistician at the 
Swiss Federal Institute of Technology. The re- 
sults of these calculations are reproduced in 
Figures 5 and 6 for the recording stations on 
Swiss and Italian territory respectively. The fig- 
ure written beside the station represents the 
probability P that there would be at least the 
same result as regards an increase in precipita- 
tion if the experiment were repeated, but with- 
out any actual seeding. At the same time the 
differences of the values to 100% indicate in 
some way how much reliance we can place in 
the recorded increase in precipitation as a sign 
of the effect of seeding. 
From Figure 6 it is immediately clear that all 
the recording stations south of the Po have 
probability values of more than 50%; thus the 
amounts of precipitation gathered by these sta- 
significance from a_ statistical 
point of view in terms of the possible effects of 
seeding, a result in keeping with the supposition 
we have just made. The recording stations in the 
test area, however, present an entirely different 
picture; their probability values vary between 
30 and 0%, and in no fewer than eight cases the 
probability is less than 5%. The recording sta- 
tions involved here all lie in extremely moun- 
tainous terrain between the Magadino Plain and 
the central Alpine Massif. 
From the point of view of physical meteorol- 
ogy the result of the statistical evaluation is ob- 
viously more consistent than the earlier figures 
given for the recorded rainfall. The possibility 
of effecting an apparently strong increase in 
precipitation as a result of seeding the atmos- 
phere by means of AgI ground generators, makes 
it potentially likely that in similar orographie 
conditions hail formation can also be interfered 
with im some way. At all events it may be legiti- 
tions have no 
