An induction coil is an apparatus for changing a direct low pressure, but large quantity current from a battery into an alternating high pressure but small quantity current, which is called high tension, or high potential, electricity.

With an induction coil you can make any number of wonderful experiments such as miniature streaks of lightning, lighting up Geissler tubes, which produce brilliant and beautiful colors showing the electric discharge in gases, etc., etc. By fixing these tubes to a small electric motor 130 so that they can be revolved while the high tension current is passing through them, the effects are further heightened.

129 The L. E. Knott Apparatus Co., Boston, Mass., and The Manhattan Electric Co., Park Row, New York, sell all these things.

130 A small electric motor can be bought for $1.00 of any dealer in electrical supplies or of the Manhattan Electrical Supply Co., Park Row, New York.