Bonaventura Cavalieri

Bonaventura Cavalieri (1598 - 1647) was an Italian mathematician whose legacy includes early work on logarithms and geometry, including the rule known today as Cavalieri's principle.

Cavalieri's principle states that the volumes of two objects are equal if the areas of corresponding cross-sections are in all cases equal. Two cross-sections correspond if they are intersections of the body with planes equidistant from a chosen base plane.

It is used in the proof of the formula for the volume of a sphere.