Holy Crap, i was just watching the history channel and they had a short segment on the "mechanical television"......!!!!
I had no idea this existed as a technology.
Basically the way it works is a large wheel with small holes around the circumfrence with a light receiver transmits pulses to the reverse at the other end. I haven't found a cool video explaining how it works as good as it was demonstrated on the history channel but check out this demonstration transmission.
There are some links here http://www.bairdtelevision.com/firstdemo.html
but you might want to google some more sites using Baird+Televisor
Either way, cool thing to see demonstrated.