Aurora Tube
   The  guinea and feather tube is a long evacuated glass tube in which objects of different densities fall with the same acceleration. The addition of two electrodes turns the tube into an Aurora Tube. In this demonstration, due to Watson and dating from 1748, an electrical discharge takes place in the residual air in the tube after it has been evacuated with a  mechanical pump.

   In this example in the apparatus collection at Washington and Jefferson College in Washington, Pennsylvania, only the upper electrode is present. The lower electrode projects upward from the pump base plate onto which the tall tube is sealed with wax or grease. 

   The bottom electrode and the brass fitting at the top were connected to the terminals of an electrostatic machine, and the resulting glow and rapidly-shifting streamers from the electric discharge passing through the residual air in the tube were thought to resemble the aurora borealis.

   A closely-related device is the electric egg.

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