Dialogue Concerning the Two Chief World Systems

...only the name, content to worship shadows without further exploration, not philosophizing with their own insight, but only with the memory of four poorly understood principles.

Three principal headings will be treated. First, I will seek to show that all experiments capable of being performed upon the Earth are insufficient means to conclude its mobility, but can be adapted indifferently both to a moving Earth and to one at rest; and I hope that in this section, many observations unknown to antiquity will be revealed. Secondly, celestial phenomena will be examined, strengthening the Copernican Hypothesis <note original: "Ipotesi Copernicana">The model proposed by Nicolaus Copernicus where the Earth and planets revolve around the Sun. as if it were absolutely to emerge victorious, adding new speculations which serve for the ease of Astronomy, rather than by necessity of nature. In the third place, I will propose an ingenious fantasy. I recall having said many years ago that the unknown problem of the ebb and flow of the sea <note original: "flusso del Mare">The tides. Galileo believed that the Earth's motion provided the physical explanation for the tides, though this theory was later proven incorrect. might receive some light if the terrestrial motion were admitted. This saying of mine, flying through the mouths of men, found charitable fathers who adopted it as the offspring of their own intellect. Now, so that no stranger may ever appear who, strengthening himself with our own weapons, might reproach us for a lack of insight into such a principal event, I have judged it fit to reveal those probabilities which would make it persuasive, given the premise that the Earth moves. I hope that from these considerations the world will recognize that if other nations have navigated more, we have speculated no less; and that returning to assert the stability of the Earth, and taking the contrary only as a mathematical whim <note original: "capriccio Matematico">A phrase used to appease censors, suggesting heliocentrism is a mere calculating tool rather than a physical claim., does not arise from a lack of awareness of what others have thought, but if for no other reason, from those arguments provided to us by Piety, Religion, the knowledge of Divine Omnipotence, and a consciousness of the weakness of the human intellect.

I then thought it very appropriate to explain these concepts in the form of a Dialogue, which, by not being restricted to the rigorous observance of mathematical laws, provides a field for digressions that are sometimes no less curious than the principal argument.

Many years ago, I found myself several times in the wonderful city of Venice in conversation with Signor Giovan Francesco Sagredo, a man of most illustrious birth and sharpest intellect.