He did this by showing that the water which issues from a hole in the side or bottom of a vessel does so at the same velocity as that which a body would acquire by falling from the level of the surface of the water to that of the orifice.

This discovery was of the greatest importance to a correct understanding of the science of the motions of fluids.

He also discovered the valuable mechanical principle that if any number of bodies be connected so that by their motion there is neither ascent nor descent of their centre of gravity, these bodies are in equilibrium.
Besides making these discoveries, he greatly improved the microscope and the telescope, and invented a simple microscope made of a globule of glass.

In 1644 he published a tract on the properties of the cycloid in which he suggested a solution of the problem of its quadrature.

As soon as this pamphlet appeared its author was accused by Gilles Roberval (1602-1675) of having appropriated a solution already offered by him.
This led to a long debate, during which Torricelli was seized with a fever, from the effects of which he died, in Florence, October 25, 1647.
There is reason to believe, however, that while Roberval's discovery was made before Torricelli's, the latter reached his conclusions independently.
VI.