Coefficient of Restitution Apparatus
   The coefficient of restitution for the collision between a moving body and a rigid surface is defined as the ratio of the speed of separation to the speed of approach. 

   Early twentieth century examples of the apparatus had a glass tube centered over a steel anvil. The steel, glass or ceramic sphere was released from rest a distance a above the anvil and rebounded to a height b. Since the final velocity is proportional to the square root of the distance of drop, the coefficient of restitution is thus equal to the square root of b/a.

   This apparatus is at the United States Military Academy at West Point, New York. Records there indicate that it was made by Pixii of Paris, and was part of a set of apparatus bought by Dr. Niles of the Academy in 1829. The rigid surface is made of marble. 

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