John Logie Baird – the inventor of the television set – showed off his creation in London, 90 years ago. The original box was a gimmick for attracting shoppers in Selfridges – but was also the first mechanical TV. Very different from today’s electronic models, Baird’s device relied on spinning discs with holes in them (Nipkow discs). A transmitter shone light through the holes as the disc spun, hitting the object being ‘filmed’; the light hit a sensor that captured the pattern and transmitted an electrical signal. The signal travelled, via radio waves, to a receiver with its own Nipkow disc rotating in sync with the original, reproducing the image.