In article -
september.org, lid says...

In article b1d536d4-b8e9-431f-a989-
,
says...

Showing images extracted from a length of rust-coated
plastic tape dragged past a spinning magnetised metal disc
tilted at an angle.

If the metal disc was magnetised, the plastic tape would
carry the images for long!

OOPS! ... would NOT carry ...!

--

Terry