THE magnetron is an electronic tube that was developed at England's Birmingham University in 1940 for use in military radar.
One of the companies that began producing magnetron tubes was the American firm, Raytheon. One day one of the company's engineers, Percy Spencer, while testing a magnetron tube, reached into his pocket for a chocolate bar. He found that it had melted into a soft, gooey mass. He had sensed no heat. He wondered if radiation from the magnetron tube had melted the chocolate. He brought some kernels of corn and pointed the magnetron at them. The corn popped. Next he aimed it at an egg. It cooked so fast that it exploded.
Percy Spencer had discovered instant cooking.
Not long afterwards, the company produced Radar Range, the world's first microwave oven - a device whose main part is the magnetron.