Question

Prior to the period of discovery of electron,how did scientists knew that what charged particles were?

Answer 1

Rutherford had tried and failed back at McGill to count α particles.

A year later in Manchester, he and Geiger succeeded with two methods of observing α particles. The first method involved scintillations excited by α particles on a thin layer of zinc sulfide. They observed these through a microscope and counted the scintillations at different angles of dispersion. They also developed an "electrometer" that could demonstrate the passage of an individual α particle to a large audience.