It could be inferred that atoms consisted of electrons and a positive charge (maintaining the atoms neutral charge)
Thomson discovered the electron. As this was negatively charged, it could be inferred that atoms consisted of electrons (negative charge) and a positive charge. His suggested plum pudding model pictured the atom as a positive cloud in which electrons were embedded.
This model was superseded following the Geiger and Marsden's experiment which led to Rutherford deducing that the positive charge and most of the mass of an atom was concentrated in the nucleus.