Answer: the beam was negatively charged
Explanation: Thomson has been experimenting with cathode ray tubes. By applying a high voltage at one end of the tube he was able to initiate the flow of particles or beam from the cathode (the negatively-charged electrode) to the anode (the positively-charged electrode). The bending of the rays to the anode indicated that particles in the beam were negatively charged (since opposite charges attract) and this led to the discovery of electrons.