From Wikipedia: The engraving depicts a man, dressed as a mediaeval pilgrim and carrying a pilgrim's staff, who peers through the sky as if it were a curtain to look at the hidden workings of the universe. One of the elements of the cosmic machinery bears a strong resemblance to traditional pictorial representations of the "wheel in the middle of a wheel" described in the visions of the Hebrew prophet Ezekiel (see Merkabah). The caption that accompanies the engraving in Flammarion's book translates as "A missionary of the Middle Ages tells that he had found the point where the sky and the Earth touched...”