Demonstrations. - Hold a thick card between the terminals of a Holtz or Wimshurst machine when it is connected with the condensers, and set the machine in action. A spark will pass, and since the card is a nonconductor, the spark will tear its way through
Set a wire upright in a wooden base, and file its upper end to a point. Place over this wire a thin test tube, as in Fig. 1, and bring one terminal of the machine directly over it. Connect the wire with the other terminal, and attach the Leyden jars. When the machine is put in operation, a spark will pass and pierce the tube. If the tube is a thick one, several sparks may go from point to knob over the surface of the glass before it is pierced.
Any nonconductor, if not too thick, can be pierced by the condenser spark between the terminals of the machine. Cardboard, books, seasoned wood, etc., should be tried. Try a metal plate also. Is it pierced? Explain.
