^ From his Letter to the Grand Duchess Christina, translated in Drake (1957).

25 The instructions for censorship were drafted by Cardinal Caetani (Gingerich (1992), p. 113). The majority of the copies in Italy were censored, but it would appear that the decree had little effect in other countries (Hine (1973), Gingerich (1992), p. 79).

The Dialogue was written in Italian with the title Dialogo sopra I due massimi sistemi del mondo Toelmaico e Copernico. It was translated into English by Thomas Salusbury as long ago as 1661 and this translation was revised by Giorgio de Santillana (Galilei (1953)). A more modern translation is that of Stillman Drake (Galilei (1962)).

Fig. 7.3. The motion of sunspots. The dashed line represents the ecliptic.

Fig. 7.3. The motion of sunspots. The dashed line represents the ecliptic.

speakers, Simplicio (a traditionalist named after the sixth-century commentator on Aristotle, but whose name carried an obvious double meaning), Salviati (the spokesman for Copernicanism), and Sagredo (an open-minded man who is persuaded largely by Salviati) and the discussion takes place over a period of 4 days at Sagredo's palace. The first day consists of a systematic demolition of Aristotelian natural philosophy, showing, on the one hand, that Aristotle's physics does not stand up to logical analysis and also demonstrating how recent telescopic discoveries had undermined completely some of its basic principles. In particular, Galileo seeks to dismantle the Aristotelian distinction between the terrestrial and supralunar regions. On the second day, the discussion turns to the motion of the Earth. Aristotle's theory of motion is picked apart and Galileo refutes all the arguments usually put forward to prove that the Earth was stationary.

The advantages of the Copernican theory were discussed on the third day. This included both the arguments that Copernicus had used himself and more recent ones such as the discovery of the full range of phases of Venus and the phenomenon of sunspots. Back in his days of telescopic discoveries, Galileo had observed dark patches on the Sun which moved and, after a period of continued observation, concluded that they were on the surface of the Sun and that the

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