cosa serve? Lo spiega Galton...
Galton presenta un dispositivo simile a quello
in Natural Inheritance già nel 1877
in un suo intervento ai Proceedings of the Royal Institution,
pubblicato successivamente sulla rivista Nature,
dove lo utilizza
per illustrare il fenomeno della regressione
In Natural Inheritance, invece, Galton utilizza
l'apparecchio per illustrare in modo meccanico la genesi
della curva normale:
"The Curve of Frequency, and that of Distribution, are
convertible: therefore if the genesis of either of them can
be made clear, that of the other becomes also intelligible.
I shall now illustrate the origin of the Curve of Frequency,
by means of an apparatus shown in Fig. 7, that mimics in a
very pretty way the conditions on which Deviation depends.
The outline of the columns of shot that accumulate in the
successive compartments approximates to the Curve of Frequency,
and is closely of the same shape however often the experiment
is repeated. The outline of the columns would become more
nearly identical with the Normal Curve of Frequency, if the
rows of pins were much more numerous, the shot smaller, and
the compartments narrower; also if a larger quantity of shot
principle on which the action of the apparatus depends is,
that a number of small and independent accidents befall each
shot in its career.
Galton, pp 63-65
In rare cases, a long run of luck continues to favour the
course of a particular shot towards either outside place,
but in the large majority of instances the number of accidents
that cause Deviation to the right, balance in a greater or
less degree those that cause Deviation to the left.
Therefore most of the shot finds its way into the compartments
that are situated near to a perpendicular line drawn from
the outlet of the funnel, and the Frequency with which shots
stray to different distances to the right or left of that
line diminishes in a much faster ratio than those distances
This illustrates and explains the reason why mediocrity is