Our apparatus consists of a glass bulb with a fluorescent painted wall.
It consists of two terminals, the cathode (negative terminal) and the anode (positive terminal).
A metal cross is placed inside the tube.
Students can appreciate that when a voltage is applied across the terminals, cathode rays travel from the cathode at the rear of the tube, striking the glass front, making it glow green by fluorescence.
A metal cross in the tube casts a shadow, demonstrating that the rays travel in straight lines.
Further it can be observed that a magnet creates a horizontal magnetic field through the neck of the tube, bending the rays up, so the shadow of the cross is higher.
When the magnet is reversed, it bends the rays down, so the shadow is lower.