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 vary with her position in the universe. Galileo communicated this appearance, which entailed conclusions so important, and which he therefore wished to investigate more thoroughly before making it known, to his friend and correspondent Julian de' Medici at Prague, in an alphabetical enigma, as in the case of the singular appearance of Saturn. It was as follows:

Having fully convinced himself by nearly three months' observations that Venus and Mars exhibited phases similar to those of the moon, he made it known in two letters of 30th December to Father Clavius, at Rome, and to his former distinguished pupil Benedetto Castelli, abbot of the congregation of Monte Cassino, in Brescia; and in a letter of 1st January, 1611, he sent the following solution of the anagram to Julian de' Medici:—

In this letter he draws the important conclusions, first that none of the planets shine by their own light, and secondly "that necessarily Venus and Mercury revolve round the sun; a circumstance which was surmised of the other planets by Pythagoras, Copernicus, Kepler, and their followers, but which could not be proved by ocular demonstration, as it could now in the case of Venus and Mercury. Kepler and the other Copernicans may now be proud to have judged and philosophised correctly, and it may well excite disgust that they were regarded by the generality of men of book learning as having little understanding and as not much better than fools."

At this time Galileo was also eagerly occupied with a phenomenon which was to be a further confirmation of the