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Sidereus Nuncius (Venice, 1609), Letter to Benedetto Castelli http://www.heritage-history.com/www/heritage.php?Dirbooks&MenuItemdisplay&authorgibson&bookscientists&storyletter (1613)

“What has philosophy got to do with measuring anything? It's the mathematicians you have to trust, and they measure the skies like we measure a field.”

Galileo Galilei (1564–1642) Italian mathematician, physicist, philosopher and astronomer

"Matteo" in Concerning the New Star (1606)
Other quotes

“Surely, God could have caused birds to fly with their bones made of solid gold, with their veins full of quicksilver, with their flesh heavier than lead, and with their wings exceedingly small. He did not, and that ought to show something. It is only in order to shield your ignorance that you put the Lord at every turn to the refuge of a miracle.”

Galileo Galilei (1564–1642) Italian mathematician, physicist, philosopher and astronomer

Notes in a copy of Jean-Baptiste Morin's "Famous and ancient problems of the earth's motion or rest, yet to be solved" (published 1631), as quoted in The Crime of Galileo (1976) by Giorgio De Santillana, p. 167
Other quotes

“Alas! Your dear friend and servant Galileo has been for the last month hopelessly blind; so that this heaven, this earth, this universe, which I by my marvelous discoveries and clear demonstrations had enlarged a hundred thousand times beyond the belief of the wise men of bygone ages, henceforward for me is shrunk into such a small space as is filled by my own bodily sensations.”

Galileo Galilei (1564–1642) Italian mathematician, physicist, philosopher and astronomer

Letter to Élie Diodati (2 January 1638), as translated in The Private Life of Galileo : Compiled primarily from his correspondence and that of his eldest daughter, Sister Maria Celeste (1870) by Mary Allan-Olney, p. 279
Other quotes

“Of such are the mathematical sciences alone; that is, geometry and arithmetic, in which the Divine intellect indeed knows infinitely more propositions, since it knows all. But with regard to those few which the human intellect does understand, I believe its knowledge equals the Divine in objective certainty, for here it succeeds in understanding necessity, beyond which there can be no greater sureness.”

Galileo Galilei book Dialogue Concerning the Two Chief World Systems

In the 1661 translation by Thomas Salusbury: … such are the pure Mathematical sciences, to wit, Geometry and Arithmetick: in which Divine Wisdom knows infinite more propositions, because it knows them all; but I believe that the knowledge of those few comprehended by humane understanding, equalleth the divine, as to the certainty objectivè, for that it arriveth to comprehend the necessity thereof, than which there can be no greater certainty." p. 92 (from the Archimedes Project http://archimedes.mpiwg-berlin.mpg.de/cgi-bin/toc/toc.cgi?page=92;dir=galil_syste_065_en_1661;step=textonly) <br class="br">In the original Italian: … tali sono le scienze matematiche pure, cioè la geometria e l’aritmetica, delle quali l’intelletto divino ne sa bene infinite proposizioni di piú, perché le sa tutte, ma di quelle poche intese dall’intelletto umano credo che la cognizione agguagli la divina nella certezza obiettiva, poiché arriva a comprenderne la necessità, sopra la quale non par che possa esser sicurezza maggiore." (from the copy at the Italian Wikisource). <br class="br">Dialogue Concerning the Two Chief World Systems (1632)

“If you could see the earth illuminated when you were in a place as dark as night, it would look to you more splendid than the moon.”

Galileo Galilei book Dialogue Concerning the Two Chief World Systems

Salviati, p. 88
Dialogue Concerning the Two Chief World Systems (1632)

“To this end they make a shield of their hypocritical zeal for religion. They go about invoking the Bible, which they would have minister to their deceitful purposes. Contrary to the sense of the Bible and the intention of the holy Fathers, if I am not mistaken, they would extend such authorities until even in purely physical matters — where faith is not involved — they would have us altogether abandon reason and the evidence of our senses in favor of some biblical passage, though under the surface meaning of its words this passage may contain a different sense.”

Galileo Galilei Letter to the Grand Duchess Christina

Letter to the Grand Duchess Christina (1615)

“Copernicus never discusses matters of religion or faith, nor does he use argument that depend in any way upon the authority of sacred writings which he might have interpreted erroneously. … He did not ignore the Bible, but he knew very well that if his doctrine were proved, then it could not contradict the Scriptures when they were rightly understood.”

Galileo Galilei Letter to the Grand Duchess Christina

Letter to the Grand Duchess Christina (1615)

“If what we are discussing were a point of law or of the humanities, in which neither true nor false exists, one might trust in subtlety of mind and readiness of tongue and in the greater experience of the writers, and expect him who excelled in those things to make his reasoning most plausible, and one might judge it to be the best. But in the natural sciences, whose conclusions are true and necessary and have nothing to do with human will, one must take care not to place oneself in the defense of error; for here a thousand Demostheneses and a thousand Aristotles would be left in the lurch by every mediocre wit who happened to hit upon the truth for himself. Therefore, Simplicio, give up this idea and this hope of yours that there may be men so much more learned, erudite, and well-read than the rest of us as to be able to make that which is false become true in defiance of nature.”

Galileo Galilei book Dialogue Concerning the Two Chief World Systems

Salviati, p. 61
Dialogue Concerning the Two Chief World Systems (1632)