In the eighteenth and nineteenth centuries, private physics collections (then known as "cabinets") and teaching laboratories used a variety of instruments to illustrate what were described as "paradoxes." These devices effectively made it possible to perform astonishing experiments that appeared to contradict common sense. By prompting closer observation and analysis, the experiments overcame the initial sense of amazement and thus demonstrated to spectators that the phenomena were perfectly consistent with the laws of physics.

The best-known and most popular mechanical paradox consists of a double cone, formed by joining two identical cones at their bases. The double cone rests on a pair of inclined, diverging rails.

If the double cone is placed at the lower end of the rails, it spontaneously begins to move upward.

This apparent paradox is explained by demonstrating the property of the center of gravity of bodies, which tends naturally to move downward. Since the rails diverge, the center of gravity of the double cone, placed on the axis of rotation at the maximum diameter of the device, does not rise when the entire body seems to move up; on the contrary, the center of gravity descends.