In this experiment a gas is compressed adiabatically by a steel ball, which can move vertically inside a long uniform bore glass tube. The ball is etched until its diameter is very slightly less than that of the tube. The glass tube is about a meter long with a bore of about 3/8th of an inch. It is mounted on top of a closed volume of the gas to be studied. This volume is about 8 liters. A screen at the bottom of the tubing prevents the steel ball from dropping out; an electromagnet can hold the steel ball at the top of the tubing. The pressure inside the volume is equal to one atmosphere. Then the steel ball is released from the electromagnet, it will oscillate inside the glass tube provided the glass tube is made accurately vertical. The period of these oscillations will depend on the mass of the ball and the force constant of the gas. Since the compression is adiabatic, this force constant will be a function of gamma (the ratio of the specific heat of gases). The measurement of gamma can also be made by observing the distance through which the ball drops until it comes to a stop. The change in the potential energy of the ball wi11 then be equal to the integral of P dv. The experiment is normally performed using two sets of apparatus: one filled with helium, and the other filled with air. In this way one can save the time needed to flush out the air from one of the pieces of apparatus.