PONTIFICIAE ACADEMIAE SCIENTIARVM SCRIPTA VARIA - 23
casting models, whereas other areas are more or less white spots on
the map of successful model building. This point of view goes to
the core of our proceedings: The very theme of our Study Week
makes a challenge to econometrics to give evidence how far our
science has reached towards the goal of valid explanatory and fore-
casting models in two areas of paramount importance: economic
growth and business cycles.
I should like to develop this point a bit more. Let us take very
briefly one example: meteorology. Fact-finding includes of course
everything about the weather. The theory of meteorology has deve-
loped gradually, but it is rather recently that explanatory models
were built that could be exploited for reliable forecasts. The breakth-
rough was the thermodynamic theory of cyclones, founded by the
Bergen school around 1918, with J. BJERKNES and T. BERGERON as
leading names.
Cold r
——,
Warm
With reference to the graph, the theory says that cyclo-
nes tend to develop on the border between cold polar air and
warm equatorial air; on the northern hemisphere the cyclones move
eastwards, go toward culmination in some few days, and then dissolve
in an occlusion of the warm front and the cold front. On the basis
of the thermodynamic theory the forecasting techniques have gra-
dually improved and become more reliable. Here is a clearcut case
where we have seen an important development in model building in
the short span of some twenty years, during which all three levels
of model building have come into the picture. Two points of general
‘1] Stone - pag. 092