It was observed by Galilei that a person on a uniformly moving ship has the impression of being at rest and sees a heavy body falling vertically downward.[3] This observation is now regarded as the first clear statement of the principle of mechanical relativity. Galilei saw that from the point of view of a person standing on the shore, the motion of falling downwards on the ship would be combined with, or added to, the forward motion of the ship.[4] In terms of velocities it can be said that the velocity of the falling body relative to the shore equals the velocity of that body relative to ship plus the velocity of the ship relative to the shore.