Eighty-one years ago today, on October 8, 1945, the Raytheon company filed a US patent for Percy Spencer’s microwave cooking process, an invention born of pure accident.

Spencer, a self-taught engineer working on radar equipment, noticed that a candy bar in his pocket had melted while he stood near an active magnetron. Curious, he tested the effect on popcorn kernels, which popped, and then on an egg, which exploded in a colleague’s face.

The patent was granted in January 1950. The first commercial microwave oven, the Radarange, arrived in 1947. It stood six feet tall, weighed 750 pounds and cost about 5,000 dollars, limiting it to restaurants and railway cars.

It took two more decades for the microwave to reach home kitchens. In 1967, Amana introduced a countertop model for 495 dollars, and the appliance soon became a fixture of modern life.

Spencer, who never finished school, received a two-dollar gratuity from Raytheon for the invention and no royalties.