I want one of them! Looks like writing old style coding sheets, but for sound.
There's a bit more text in this report - and the original painting-on-glass version (and some ancient BBC radio from the '70s):
http://www.bbc.co.uk/news/technology-36651270
I vaguely remember seeing this (in the science museum) a year or two back. I stared at it for ages, and was no closer to working out how it worked