"When Copernicus, instead of leaving the earth at rest in the center of the world, gave it not only two rotations on its own center, but... an annual revolution around the sun, astronomers were able to maintain that these hypotheses are not... realities, that it suffices for them to be fictions by which the phenomena are saved in a simpler... more exact manner than... Ptolemy's devices. But physicists did not willingly use this loophole; they not only saw in the system of Copernicus a model enabling them to construct new tables of celestial movements, they also imagined something... that claims to reveal a truth. They imagined that the earth is a planet of the same nature as Venus, Mars, or Jupiter. The problem... can each of the... wandering stars be a world similar to the world in which we are living, having at its center an earth covered by water, surrounded by air?"