Near about 2600 years ago (600 B.C.E.) it was noticed by Greeks tat amber (a yellowish-brown resin which hardens to a stone like material) when rubbed with silk possessed the property of attracting small pieces of cork, paper etc. In Greek the ember is named as electron. Then again in 1600 C.E. Dr. Gilbert showed that there were many substances e.g. ebonite, sealing wax, glass etc. are when rubbed on silk or fur, they also possessed the same property. He called this phenomenon, which produces the property of attraction of small pieces of cork, paper, etc. in glass or amber as Electricity. The substance possessing this property were called as Electrified or charged with electricity.
Hence electricity may be defined as mysterious agent which causes the property of attraction in substances.
The substances which are not electrified or uncharged when rubbed on silk or fur or flannel are called Neutral.
It has been experimentally determined that when glass rod is rubbed with silk and is suspended and when an ebonite rod rubbed with flannel is brought near it an attraction is observed, but when another glass rod is rubbed with silk is brought near it, repulsion is observed. The result of this experiment can be summed up thus:-
- There are two different types of charges which are attained by the glass and ebonite rod respectively.
- The bodies which attend similar charges repel each other.
- The bodies having opposite charges attract each other.
Dufay called the type of charge on glass as vitreous (obtained from latin name of glass vitreum) and the type of charge on ebonite as resinous. But these names were soon dispensed with as it is not always the glass will have same kind of charge. When glass is rubbed with silk it attains vitreous electricity but when it is rubbed with flannel it attains resinous electricity. Benjamin Franklin called the charge attained by glass rod rubbed with silk as positive and the charge attained by ebonite rod rubbed with flannel as negative. This Convection is adopted even now although there is no reason why the charge on glass rod rubbed with silk should be called as positive charge and not negative charge.