The oldest ancestor of the point-contact transistor was the crystal detector, used in early wireless sets.

ECONOMIST: The middle age of the transistor

So little wonder that at the time of the broadcast only about 200 receiving licences had been sold, although it is possible that many more tuned in on homemade crystal "cat's whisker" sets.

BBC: Broadcasting in Wales: 90 years since BBC went on air

Each glass sheet has rows of conducting wires running across it, and the two sets of wires are at right angles, so that a voltage can be applied across the liquid crystal at any chosen intersection.

ECONOMIST: Just press print