He made mathematical calculations to prove this, and appears to have reached the definite conclusion that the earth does move--or what amounts to the same thing, that the sun does not move.

Muntz is authority for the statement that in one of his writings he declares, "Il sole non si mouve"-- the sun does not move.( 2) Among his inventions is a dynamometer for determining the traction power of machines and animals, and his experiments with steam have led some of his enthusiastic partisans to claim for him priority to Watt in the invention of the steam-engine.

In these experiments, however, Leonardo seems to have advanced little beyond Hero of Alexandria and his steam toy.

Hero's steam-engine did nothing but rotate itself by virtue of escaping jets of steam forced from the bent tubes, while Leonardo's "steam-engine" "drove a ball weighing one talent over a distance of six stadia." In a manuscript now in the library of the Institut de France, Da Vinci describes this engine minutely.

The action of this machine was due to the sudden conversion of small quantities of water into steam ("smoke," as he called it) by coming suddenly in contact with a heated surface in a proper receptacle, the rapidly formed steam acting as a propulsive force after the manner of an explosive.