"AndyW" wrote in message
...
On 19/02/2014 09:32, gareth wrote:

LED or nitro-benzine as the polariser?
Polariser?

To my eternal regret, because I disposed of them 38 years ago, I had a
pile of "Amateur Wireless" from the 1930s within which were designs
for mirror-drum scanners, and the modulation was not by a neon light
but with a constant light source which was then modulated by a series
of polarising filters, with one being variable to rotate the polarisation.

ISTR (38 years ago!!!) that the liquid used was nitro-benzene