How did the concept of positive and negative charge originate before the discovery of an electron? My question is related to the historical aspects.
In the 1700s it was established that materials (especially those that we now call 'electrical insulators) when rubbed with other suitable materials, could be divided into two groups. All the rubbed materials repelled materials in the same group, but attracted materials in the other group. Benjamin Franklin called the group containing glass rubbed with silk "positively charged" and the group containing amber (fossilised resin) rubbed with fur "negatively charged". [He didn't think of positive charge and negative charge as of equal status as we now do; rather he thought of negative charge as an absence of the real stuff: positive charge!]
The reason that we now say that an electron has a negative charge and the proton has a positive charge goes back to Franklin's arbitrary decision to say that glass rubbed with silk is positive and amber rubbed with silk is negative. If you hold a rubbed lump of glass near an electron beam it attracts the beam; if you hold a rubbed lump of amber near the beam it repels it!