Image on black and white television is deflected by a magnet, not unlike the Maltese Cross.
What it shows:
The television is basically a sophisticated cathode ray tube. The electron beam in the TV is influenced by magnetic fields in the same way as in Crookes tubes.
How it works:
The image on a black & white TV is formed by a single electron gun scanning the screen. Holding a strong magnet to the side or in front of the screen deflects the beam from its regular sweep pattern, distorting the image.
Setting it up:
We use and old Conrac™ black and white TV monitor and abuse it with a samarium-cobalt magnet, although any strong horseshoe magnet would do equally well.
This is recommended for old black and white TVs and not recommended for color ones (it's not meant to damage them, but we're not rich enough to put it to the test!).