Electrification by friction
When a glass rod is rubbed with a silk cloth some electrons from the glass attach themselves to the silk. Consequently, the glass becomes positively charged and the silk negatively charged. Likewise when ebonite is rubbed with fur electrons are transferred
from fur to ebonite, thus making the ebonite negative and the fur positive. Why this happens, and why the electrons go from glass to silk and from fur to ebonite and not in the reverse direction, is not at present understood.