7
LEARNING GUIDE
Invention and Refinement
The earliest metal detectors were large and inefficient, but
by the 1920s portable versions of the machines began to
appear. The first portable metal detector patent was issued
in 1925, and three years later the American businessman
Shirl Herr patented a device that could detect metals buried
as deep as eight feet.
COOL SCIENCE FACT
:
In 1974 hobbyist Roy Lloyd discovered a high school class ring from
1926 inscribed with the initials “M.B.” After doing some research he
reunited the ring with its owner, Miles Baker, who had lost it off a pier
in Lake Johnson, Florida, nearly a half century earlier.
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