At very low pressures and at extremely high voltages, we can observe the electrical discharge through the gases.
When a high voltage is applied across, current starts flowing from cathode to anode terminal through a stream of particles present.
However when we make a small hole in the anode part and cover the background area with a florescent material, we start observing bright spots on it.
The cathode rays start from cathode and move towards the anode.
These rays themselves are not visible but their behavior can be observed with the help of certain kind of materials (fluorescent or phosphorescent) which glow when hit by them.
British physicist J.J. Thomson conducted an experiment to calculate the ratio of electrical charge (e) to the mass of electron (me ). He used an apparatus of CRT and used electrical and magnetic fields (perpendicular to each other) to deflect the electrons.
The strength of the electrical or magnetic field — the deflection of electrons from its original path increases with the increase in the voltage across the electrodes, or the strength of the magnetic field.
When he applied only electrical field to the rays, the deflected rays hit point A. When only magnetic field was applied, rays hot point C.