How Like Repels Like.
—Electrify two strips of newspaper this time and hold them together by the ends. Instantly the free ends of the papers will fly apart for like signs of electricity repel each other.
That is, since both strips of paper are positively electrified and hence are of like signs, they repel each other. If they were negatively electrified they would repel each other just the same. In either case it shows that there is a force acting across the space between the two strips of paper.
Making Experiments With Apparatus.
—With a dry battery of two or three cells, an electric bell, a common steel magnet and an electromagnet, all of which you can easily make or buy[134] for a dollar or so, you can provide entertainment enough for ¹⁄₂ an hour’s demonstration, and food for thought to last a year.
[134] The L. E. Knott Apparatus Co., Boston, Mass., and The Manhattan Electric Co., Park Row, New York, sell all these things.
The Induction, or Spark Coil.
—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[135] so that they can be revolved while the high tension current is passing through them, the effects are further heightened.
[135] 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.