"[I]n 1897 Thomson... detected a deflection... by electric forces between the rays and the electrified metal plates. ...due largely to the use of better vacuum pumps ...to where the effects of residual gas ...became negligible. (Some evidence for... deflection was [also] found... by Goldstein.) [D]eflection was toward the positively charged plate... away from the negatively charged one, confirming Perrin... that the rays carry negative electric charge."