A hundred years ago this month, the October 1921 issue of Popular Science showed this signaling device for use by the military. It provided a level of security, because its light beam was visible only over a small area. It’s a very simple idea–it consists of a telescope with a flashlight bulb mounted inside at the focal point. It was easily aimed by looking through the telescope. The bulb’s filament was visible, and it was simply a matter of lining it up so that was visible over the spot where you wanted your signal seen.

Students looking for a science fair project could easily recreate this.  All that’s needed is a toy telescope like the one shown here.  It can be carefully disassembled and the bulb place inside.  You can use the bulb from an old flashlight, or buy the bulb separately.  For this project an old-fashioned incandescent bulb will work better than an LED.

You’ll also need some hookup wire and batteries.  While not absolutely necessary, a battery holder will make the job a lot easier.  Normally, for a science project involving light bulbs, it’s most convenient to get a socket for the bulb.  However, in this case, the socket might not fit.  Therefore, the best option would be to solder the wires directly to the bulb.  A soldering iron, complete with solder and everything else you need, is surprisingly inexpensive.

To send Morse code, you’ll also need a small pushbutton switch.

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