![background image](http://html1.mh-extra.com/html/national-geographic/junior/junior_instructions-and-learning-manual_3382579010.webp)
8
These instruments proved their worth when Admiral Byrd
used them in Antarctica to locate materials left behind
by earlier expeditions. Over the next several decades
technological improvements turned the metal detector into a
practical device for hobbyists. Batteries got smaller, circuits
got better, and the whole machine got lighter and smaller
as transistors replaced clunky vacuum tubes. Additional
refinements enabled metal detectors to work underwater
and to distinguish between different metals. Some detectors
can be immersed as deep as 200 feet underwater for
detecting the sea bed, and some even have built-in GPS.
Don't try this with
our metal detector!
It's meant for use
on land only.