"I experimented with all possible maneuvers-loops, somersaults and barrel rolls. I stood upside down on one finger and burst out laughing, a shrill, distorted laugh. Nothing I did altered the automatic rhythm of the air. Delivered from gravity and buoyancy, I flew around in space."

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I would beg the wise and learned fathers (of the church) to consider with all diligence the difference which exists between matters of mere opinion and matters of demonstration. ... [I]t is not in the power of professors of the demonstrative sciences to alter their opinions at will, so as to be now of one way of thinking and now of another. ... [D]emonstrated conclusions about things in nature of the heavens, do not admit of being altered with the same ease as opinions to what is permissible or not, under a contract, mortgage, or bill of exchange.

— Galileo Galilei