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La Macchina di Galton
 La Macchina di Galton -> Che cosa è?

Che cosa è la macchina di Galton?

Disegno di Galton del suo macchinarioIl suo inventore, Sir Francis Galton lo descrive così:

"It is a frame glazed in front, leaving a depth of about a quarter of an inch behind the glass. Strips are placed in the upper part to act as a funnel. Below the outlet of the funnel stand a succession of rows of pins stuck squarely into the backboard, and below these again are a series of vertical compartments.

A charge of small shot is inclosed. When the frame is held topsy-turvy, all the shot runs to the upper end; then, when it is turned back into its working position, the desired action commences. Lateral strips, shown in the diagram, have the effect of directing all the shot that had collected at the upper end of the frame to run into the wide mouth of the funnel.

The shot passes through the funnel and issuing from its narrow end, scampers deviously down through the pins in a curious and interesting way; each of them darting a step to the right or left, as the case may be, every time it strikes a pin. The pins are disposed in a quincunx fashion*, so that every descending shot strikes against a pin in each successive row. The cascade issuing from the funnel broadens as it descends, and, at length, every shot finds itself caught in a compartment immediately after freeing itself from the last row of pins."

Galton[1889], p. 63

Disposizione a quinconce

* Quincunx: la parola deriva dal latino "quinque", cinque. La disposizione a quinconce si realizza spostando ogni fila di chiodi rispetto alla precedente in modo che i chiodi cadano nel punto di mezzo di quelli della fila sovrastante. In tre file di chiodi si ha in pratica la stessa disposizione dei punti della faccia n. 5 di un dado. Da qui l'altro nome del macchinario: quinconce.


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