During his last stay at Rome, at the suggestion of Cardinal Orsini, he had written a treatise on the tides in the form of a letter to that dignitary, dated January 8th,[160] in which he expressed his firm conviction, erroneously as we now know, that this phenomenon could only be explained on the theory of the double motion of the earth. He represented it as an important confirmation of the truth of it. In May, 1618, he sent a copy of this treatise to the Archduke Leopold of Austria, who was friendly to him, and was a brother of the Grand Duchess. But as since it was written the decree of March 5th had been issued, which only permitted discussion of the subject as a hypothesis, Galileo thought it advisable to add a sort of accompaniment to his treatise, in which he took the utmost pains to comply with the conditions imposed by the Church on her dutiful and orthodox son. He wrote:— “With this I send a treatise on the causes of the tides, which I wrote rather more than two years ago at the suggestion of his Eminence Cardinal Orsini, at Rome, at the time when the theologians were thinking of prohibiting Copernicus’s book and the doctrine enounced therein of the motion of the earth, which I then held to be true, until it pleased those gentlemen to prohibit the work, and to declare that opinion to be false and contrary to Scripture. Now, knowing as I do, that it behoves us to obey the decisions of the authorities, and to believe them, since they are guided by a higher insight than any to which my humble mind can of itself attain, I consider this treatise which I send you merely to be a poetical conceit, or a dream, and desire that your Highness may take it as such, inasmuch as it is based on the double motion of the earth, and indeed contains one of the arguments which I have adduced in confirmation of it. But even poets sometimes attach a value to one or other of their fantasies, and I likewise attach some value to this fancy of mine. Now, having written the treatise, and having shown it to the Cardinal above-mentioned, and a few others, I have also let a few exalted personages have copies, in order that in case any one not belonging to our Church should try to appropriate my curious fancy, as has happened to me with many of my discoveries, these personages, being above all suspicion, may be able to bear witness that it was I who first dreamed of this chimera. What I now send is but a fugitive performance; it was written in haste, and in the expectation that the work of Copernicus would not be condemned as erroneous eighty years after its publication. I had intended at my convenience, and in the quiet, to have gone more particularly into this subject, to have added more proofs, to have arranged the whole anew, and to have put it into a better form. But a voice from heaven has aroused me, and dissolved all