When a positively charged plate is held near a cathode ray beam, the beam bends towards the plate. This observation leads to the following conclusion:

The cathode rays are composed of negatively charged particles.

Here's why:

* Opposite charges attract: A positive plate attracts negative charges. The fact that the cathode ray bends towards the positive plate indicates that the particles within the ray are negatively charged.

* Like charges repel: If the cathode rays were positively charged, they would be repelled by the positive plate and bend away from it.

This experiment was crucial in J.J. Thomson's discovery of the electron. It demonstrated that the cathode ray was not just a wave of light, but was composed of tiny, negatively charged particles that we now call electrons.