  One notable success in the experimental domain is his performance of the Galilean test of dropping a stone from the mast of a moving ship, recorded in De Motu. Once dropped, Gassendi shows, the stone conserves its horizontal speed (equal to that of the ship, before being released) and its motion describes a parabola given its downward fall. This result successfully refutes one simple anti-Copernican argument, by showing that the Earth can move without superadding motion to terrestrial objects otherwise in motion (which superaddition, opponents of Copernicanism correctly maintained, would generate much havoc in the motion of terrestrial objects). This much Galileo surmised in his original thought experiment, though the performance was excellent publicity for the Galilean perspective and an opportunity for Gassendi to think through the issues at stake.