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PONTIFICIAE ACADEMIAE SCIENTIARVM SCRIPTA VARIA - 28 
logy, history and economics so as to be mainly of a nonexperimeatal 
kind, It is very true that experiments also belong in the picture, 
but that was just to simplify. 
To comment more in detail on the question about meteorology, 
[ would say that while most of the fundamental law of physics can 
be demonstrated by controlled experiments, the empirical evidence 
on the thermodynamic theory of cyclones is essentially nonexperi- 
mental — you do not experiment with cyclones on a world global 
scale, and the same holds true of many other meteorological appli- 
cations of physics. At the same time there are elements of genuine 
controlled experiments in meteorology — rainmaking devices are a 
case in point. The experiments of rainmaking provide material for 
model building at the descriptive and explanatory as well as the 
forecasting level, showing that experimental and nonexperimental 
evidence combine and merge at all levels of model building, including 
the level of forecasting. 
FRISCH 
I want to congratulate both Prof. STONE and Prof. MAHALANOBIS 
for their presentations, I am very much in agreement about what 
they say about the philosophy of models and as a matter of fact 
they have relieved me of a good portion of my own task when I am 
going to speak in a few days from now. Of course I also agree 
completely to the three points which Prof. Worp put before us — 
the three levels of aspiration so to speak, but — and this is so- 
mething which I took down while he was talking — there is a fourth 
point which must absolutely be added (and here of course I am 
talking in the same vein as Prof. MAHALANOBIS) namely the analysis 
of the decision on action. What are we going to do? That of course 
depends on what we would like to see happen sometime in the future 
and as a matter of fact this will really be a very essential point in 
my presentation, This is the essence of the distinction between a 
forecasting model and a decision model. I understand that Pro- 
"1] Stone - pag. 98