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Percy Spencer, just after the end of World War II, was working on a power tube for the Raytheon Corporation. Nothing might have come of it, if it weren’t for one heroic chocolate bar that gave its life for modern society.

The magnetron was designed to power radar sets. Obviously these were important during the war, and after the war, Raytheon wanted to continue their research, taking advantage of the booming economy. While Spencer worked, he walked in front of the tube. This was not wise move, but Spencer might not have known how inadvisable it was had he not had a chocolate bar in his pocket. It’s not clear whether he decided soon after that it was time for a snack or whether he felt something warm and trickly in his pants and looked down to see alarming brown liquid. Either way, he noticed that the chocolate bar had turned to goo.

I've heard all different versions of this. In fact, this article is the first time I've read them all from the source going on to say,

Being an inquisitive sort, he grabbed some popcorn kernels, put them in a bag, and waved them in front of the tube. The kernels popped without any discernable heat being applied to them. Still not satisfied, he grabbed an egg and waved it front of the tube. It exploded all over a colleague (who was hopefully not also in front of the tube). It was clear they were on to something.

The one commonality is always someone had something edible in their pocket and it melted and microwaves were discovered and found to be applicable for foods? Is this true, or urban legend?

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    I would be skeptical of this story just because the microwave would've had the same effect on the human flesh that was apparently in both cases on the effective range. – Communisty Apr 30 '18 at 8:17
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    I've never heard that story before. The one I've heard about the origins of microwave ovens pertain to birds being cooked alive by early radar installations such as the Home Chain system installed along the British coast. Given how different these stories are I'm wondering if it's almost some sort of regional folk-story? – GordonM Apr 30 '18 at 11:24
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    In fact, if Wikipedia can be taken as a reliable source (make your own call on that one!) then the first applications of radio waves as a heating/cooking technology pre-dated radar by a decade or more. en.wikipedia.org/wiki/Microwave_oven#History (though it does also mention the above story as the first actual cooking of something with actual microwaves) – GordonM Apr 30 '18 at 11:26
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    Certainly when I was in engineering school in the late 60s I was warned that certain pieces of military surplus radar equipment should not be powered on with anyone nearby. If this character was cooking his chocolate bar he was also cooking other stuff in his pants. – Daniel R Hicks May 1 '18 at 0:16
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    Particularly his belt buckle or other metal accessories. This story seems completely implausible. – kbelder May 1 '18 at 17:56
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The origin of this story seems to be a 1958 Reader's Digest article, "Percy Spencer and His Itch to Know", written by Don Murray:

One day a dozen years ago [Percy Spencer] was visiting a lab where magnetrons, the power tubes of radar sets, were being tested. Suddenly, he felt a peanut bar start to cook in his pocket. Other scientists had noticed this phenomenon, but Spencer itched to know more about it.

He sent a boy out for a package of popcorn. When he held it near a magnetron, popcorn exploded all over the lab. Next morning he brought in a kettle, cut a hole in the side and put an uncooked egg (in its shell) into the pot. Then he moved a magnetron against the hole and turned on the juice. A skeptical engineer peeked over the top of the pot just in time to catch a faceful of cooked egg. The reason? The yolk cooked faster than the outside, causing the egg to burst.

Now, it's not clear to me from this if the story is true or not (and we may never know). Was this something that Spencer told Murray? It doesn't say. It does match with what his grandson, Rod Spencer, allegedly said about him always carrying "a peanut cluster bar" to feed squirrels (again, not sure where that quote comes from, so treat it skeptically). And of course, it makes sense that all the food was brought in from outside the lab, but that doesn't mean it's real.

According to this article (paywalled), the magnetrons that were being manufactured operated on bands anywhere between 1 to 10 GHz, so it might not have been the same frequency as home microwaves. According to interviews conducted by the author of that article, other scientists that worked with Spencer noticed "warmth and therefore heating of objects on their person."

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