If you experiment further you will find that two sticks of sealing-wax will repel each other.
Fig. 26.—Similarly Electrified Bodies Repel Each Other. Dissimilarly Electrified Ones Attract Each Other.
This experiment indicates that there are two kinds of electrification: one developed by rubbing glass with silk and the other developed by rubbing sealing-wax with flannel.
In the first instance, the glass rod is said to be positively electrified, and in the latter case the sealing-wax is negatively electrified.
The same law that applies to magnetism also holds true in the case of static electricity, and similarly electrified bodies will repel each other and dissimilar ones attract.
The Electrophorus is an instrument devised by Volta in 1775 for the purpose of obtaining static electricity.
Fig. 27.—The Electrophorous
It is easily constructed and will furnish a source of electricity for quite a number of interesting experiments. An electrophorus consists of two parts, a round cake of resinous material cast in a metal dish or pan, and a round metal disk which is provided with an insulating handle.