This is the story of a mechanical tradition, so let us begin with a machine (Figure 1.1).1 Take a hollow bronze sphere, drilled at two diametrically opposite points to allow the insertion of two L-shaped tubes, carefully soldered to the outside of the sphere so that it remains completely sealed except for their ends. Add one more tube, in the plane perpendicular to the first two, and a socket for a pivot opposite that. Place the sphere on a covered vat of boiling water so that the third tube conducts steam into the sphere, where it can be ejected from the L-shaped tubes. Once the steam begins to flow, the sphere will rotate on the pivot, propelled by the steam leaving the tubes.