Ten months before his death, thanks to an indiscreet question from one of his former pupils, a last opportunity occurred of speaking of the Copernican system. Francesco Rinuccini, Tuscan resident at Venice, and afterwards Bishop of Pistoja, having apparently forgotten that the master had solemnly abjured that opinion, and had even been compelled to promise to denounce its adherents wherever he met with them to the Inquisition, informed him in a letter of 23rd March, 1641,[1] that the mathematician Pieroni asserted that he had discovered by means of the telescope a small parallax of a few seconds in some of the fixed stars, which would place the correctness of the Copernican system beyond all question. Rinuccini then goes on to say, in the same breath, that he had lately seen the manuscript of a book about to appear, which contained an objection to the new doctrine, and made it appear very doubtful. It was this: because we see exactly one half of the firmament, it follows inevitably that the earth is the centre of the starry heavens. Rinuccini begs Galileo to clear up these doubts for him, and to help him to a more certain opinion.
This was the impulse to Galileo's letter of 29th March, 1641,[2] which, as Alfred Von Reumont truly says,[3] whether jest or mask, had better never have been written. There is no doubt that it must not be taken in its literal sense. Precisely the same tactics are followed as in the letter which accompanied the "Treatise on the Tides," to the Grand Duke of Austria in 1618, and in many passages of the "Dialogues on the Two Systems." Galileo conceals his real opinions behind a thick veil, through which the truth is only penetrable by the initiated. The cautious course he pursued in this perilous answer to Rinuccini is as clever as it is ingenious, and appears appropriate to his circumstances; but it does not produce a pleasant impression,
