Arch Related Inventions: Radar and
the Microwave Oven

Raytheon and Percy Spencer 1894-1970

What happens when a candy bar gets too hot? It melts, of course! That is precisely what happened in 1946, when Percy Spencer discovered the idea behind microwave cooking. Spencer, a self-taught engineer who held 150 patents, is one of the most creative inventors in American history.

Spencer was involved in Raytheon's World War II defense work; in fact he was responsible for several inventions that helped the Allies in their decisive victory in Europe. He became involved with magnetron production when the Pentagon sent a British Army leader to Boston to meet with Spencer and Raytheon. Spencer, in one weekend, solved the problem of mass-producing the then hand-built magnetron tubes, enabling many more radar sets to be built; a decisive factor in winning the Battle of Britain.

While working with magnetron tubes, Spencer stumbled upon an invention that changed life in America. One afternoon in 1946, Spencer noticed that when he worked in front of the magnetron, his favorite chocolate bar snack (stuck in his back pocket) melted. Guessing that the heat from the magnetron caused the bar to melt, Spencer tried a bag of popcorn. Sure enough, it popped!

Using Spencer's ideas, Raytheon began to produce the Radarange, selling mainly to commercial businesses. But the appliance was huge (the size of a refrigerator) and very expensive to make ($100,000), and not very appealing to homeowners. After many design changes and the development of cheaper, longer-lasting magnetron tubes, a small version, now known as the microwave, began to make its way into homes in the mid-1960s with Raytheon's Amana Division leading the way.

Spencer was the son of an itinerant mill worker in Maine. Orphaned at 8, he never finished elementary school. He came to Boston after World War I and was hired by Raytheon founders Laurence Marshall, C. G. Smith, and Prof. Vannevar Bush (electrical engineering at MIT). Marshall had been Bush's college roommate at Tufts University, and Smith had done his graduate studies at Harvard. Raytheon is a prime example of how Boston's strong educational tradition-in this case MIT, Harvard, and Tufts-has helped to provide a fertile field for innovation and collaboration. Spencer, of course, contributed his raw talent.

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