394 
mate to assume that, in the kind of conditions 
existing in the test area, dispersed silver iodide 
from ground generators is able to rise to heights 
where it can have an active nucleating effect. 
This means that when the experiment has been 
continued for a sufficient length of time it will 
be possible to arrive at. some definite decision as 
to the effects, whether positive, negative, or 
neutral, of silver-iodide seeding on hail forma- 
tion. 
DISCUSSION 
REFERENCES 
Darurnc, D. A., The Kolmogorov-Smirnov, Cra- 
mer-von Mises tests, Ann. Math. Statistics, 28, 
823-838, 1957. 
SAncer, R., Fr. Sprinc, W. Staus, anp J. C. THAMs, 
Grossversuch III zur Bekimpfung des Hagels im 
‘Yessin, Eidg. Kommission zum Studium der 
Hageibildung und der Hagelabwehr, Abteilung 
fiir Landwirtschaft des EVD, Bern, Tatigkeits- 
bericht no. 10, pp. 1-111, 1957 and no. 11, pp. 1- 
105, 1958. 
Discussion 
Dr. O. Essenwanger—Did 1 understand cor- 
rectly that you said there is no statistical evalua- 
tion? 
Prof. R. Sdnger—We have too little data to 
undertake an evaluation of the occurrence of 
hail. 
Dr. Essenwanger—That is what I wanted to 
say. The more samples you have, the more pos- 
sibilities exist to get a significant result. One 
may get an insignificant result because of the 
shortness of samples? 
Capt. H. T. Orville—Were your generator sites 
exactly the same in 1957 and 1958? 
Prof. Sdnger—We decided not to change any- 
thing during the whole period, mainly because 
of statistical reasons. 
Mr. Jerome Namias—I do not mean to stick 
my head into a hornets nest here, but I have 
often wondered about the question of evaluating 
rain-making experiments from the rainfall rec- 
ords themselves. While I think the techniques 
used are legitimate from the standpoint of sta- 
tistics, there are two possibilities that I would 
like to suggest for evaluations of this sort. One 
is that the synoptic characteristics of the periods 
be considered. Nature sometimes has a way of 
defeating our procedures of randomization. It 
might be that, because of the small number of 
seeding cases, during one long-period weather 
regime, the recurrent synoptic situation favors 
one period with respect to another. The second 
thought I have to offer is perhaps more contro- 
yersial. One is often dissatisfied with the knowl- 
edge that weather forecasting has amassed up to 
the present. Nevertheless, there is positive skill 
on the part of the forecaster. I have wondered, 
therefore, why the forecaster can not be con- 
sidered as some sort of a control in evaluating 
seeding effects. If one has sufficient cases over a 
long period, and the forecaster has positive skill, 
one can ask him to predict amounts over a long 
period of time and the discrepancy between his 
predictions and the observed amounts can be 
evaluated in terms of the effect of seeding opera- 
tions. 
Or it can be done on a ‘post-mortem’ basis. 
Give him various maps, let him make predictions 
or hindeasts of what might have happened, and 
use these as a control. So, I think there are 
methods other than statistical that might be put 
to use throughout the world. 
Prof. Sanger—Every year we prepare a large 
report including the meteorological situations, 
but here I present only the statistical part. It is 
also our intention to discuss the observations 
made in a manner similar to Mr. Namias’ pro- 
posal. On the other hand we want to have an 
evaluation which is completely free of subjectiv- 
ity. 
Dr. Fred Decker—Will your future work on 
this include enough observation on hail so that 
you establish the area where the hail fell? 
Prof. Sdnger—We intend to evaluate the hail 
fall in three areas separately, and also with re- 
gard to intensity. Our observations have been 
made according to the international scale of in- 
tensity. 
Dr. Helmut Weickmann—I am particularly 
happy about your comment, Mr. Namias, be- 
cause it emphasizes the importance of meteorol- 
ogy in the problem of the evaluation of the 
seeding experiments. I like to recall the days of 
the great argument between Dr. Langmuir and 
the U.S. Weather Bureau on the subject of the 
generation of a seven-day rainfall period as a 
consequence of periodic seeding with one Agl 
generator in New Mexico. In those days the U.S. 
