In 1945, Percy Spencer, self-taught engineer, was investigating alternative uses of the magnetron, a unit developed to generate microwaves for radar transmissions. While testing a magnetron, Spencer found that a chocolate bar in his pocket had melted. He experimented further with an egg, which exploded, and with popcorn, which popped all over the room. Spencer then constructed a metal box and fed microwaves in from a magnetron, and the microwave oven was born. In 1947, his employer (Raytheon) built the "Radarange", the first commercial water-cooled microwave oven. It was almost 2 m tall, weighed 340 kilos and cost US $5000. Not till the 1970s did microwave ovens began to outsell traditional ovens but, by now, 90% of US households feature a microwave oven.

(Entry contributed by Julia Hall.)