This picture I saw long ago in a schoolbook. It should show the world view in the Middle Ages. In this view there's a point where the earth and the heavens met. The earth is a disc. And behind the firmament is a second sky (Cosmos, Kristallhimmel, Feuerhimmel) with the cosmic machinery. The wheel in a wheel is a symbol for God. Now to some new things (for me): This is not a woodcut from the Middle Ages. It is a book-illustration of Camille Flammarion's 1888 "L’atmosphère. Météorologie populaire". More information here: http://en.wikipedia.org/wiki/Flammarion_engraving. The artist is unknown. It is a wood engraving, but I think, its based on a ink drawing.