Some history really does need to be rewarmed.
January 24 marks the anniversary of the granting of the patent for the microwave oven, “Method of treating foodstuffs.” Do your texts even refer to this by-product of World War II? What benefits of microwave ovens can your students come up with? Will they offer the apocryphal question about how Native Americans could possibly have invented popcorn with their wood-fired microwave ovens?
Dr. Percy L. Spencer noted that a chocolate bar in his shirt pocket had melted when he was working around an operating radar tube, at Raytheon Corp., during World War II (the patent application for microwave cooking was filed on October 8, 1945). With a little experimentation, he determined the microwaves from the radar tube were rapidly cooking things — think exploding egg, think popping corn.
Drawing from the patent of the microwave oven, granted to Percy L. Spencer on January 24, 1950; courtesy the Southwest Museum of Engineering, Communications and Computation
One of the problems Spencer had to overcome was that radar tubes cooked foods way too fast. He had to tune the magnetron tubes to produce wavelengths with less energy, to heat food more slowly so the cooking could be controlled. Spencer explained this process of invention in the first page of text on the patent itself.
Perhaps one could create an interesting DBQ with only patents, tracing radio and radar through the microwave oven.
This is one device you probably can demonstrate safely in any history classroom.
Resources:
- The Spencer Microwave Oven Patent, at the Southwest Museum of Engineering, Communications and Computation (SMECC), in Glendale, Arizona
- “Who invented microwaves?” by J. Carlton Gallawa
- American Physical Society history of radar
- BBC H2G2 history of radar
- BBC H2G2 backgrounder on patents (remember that regulation of the patent process is one of the express powers of Congress from Article I of the Constitution)
- Franklin Institute history of radar
- Percy Spencer bio at Wikipedia
- “Percy Spencer and his itch to know,” story by Don Murray from the April, 1958 issue of Readers Digest
- Collection of articles about microwave ovens and microwave oven cooking from the New York Times
Millard Fillmore's Bathtub 
Amazing story really when you think that it was by chance that the power of the microwave was harnessed for domestic cooking – maybe more so that Dr Spencer realised the conection or potential of what he had experienced with the chocolate. I also have to add that Onkel Bobs post contained some very interesting information – thanks
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[…] Last year’s post on “Forgotten anniversaries.” […]
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Or the stories of the guys in the cold, frozen north with NORAD, who would sit in front of the radar transmitter to get warm. Or the geese who fly a line between two microwave towers and cook themselves.
I wondered whether Spencer lost any tissue where the chocolate bar didn’t protect him, but I suppose he wouldn’t lose much.
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Slightly OT, I worked for a number of years in microwave communications. On never forgets the urban legends that were bandied about, always involving guys working on antennas and not knowing they were active. The story goes the guy had trouble swallowing (or breathing, or just felt funny) and goes to the doctor to find this or that organ has been cooked.
Not to say there wasn’t any danger.To amuse ourselves, we hoisted hot dogs on strings, hanging them in front of the feedhorn of a refraction scatter link. It took a while as 50 watts of RF energy isn’t all that powerful, but eventually they did get hot.
IIRC the standard household microwave is tuned to the resonant frequency of water, and it’s that activity (the vibrating water molecules) that causes the food to heat. That frequency is very close to the 2.4 Ghz frequency in our 802.11 wireless networks.
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