A hundred years ago this month, the March 1916 issue of Boys’ Life magazine carried the plans for this simple heliograph. This device is capable of signalling many miles, depending of course on the altitude and whether the sun is shining. It allows the sender to flash signals using any code, although the article recommends use of the Morse code.
The heliograph consists of a mirror with a hole drilled through it (for sighting). Drilling the hole through glass was probably the most difficult part of the process, as the article points out that “any optician will drill the hole for you for a quarter or less.”
The construction details are rather straightforward, as shown by the illustration below. To use, the sender first sights the receiving station by looking through the hole, and lining the stick in front up with the destination. Then, the mirror is adjusted so that the sun is focused on the stick. To send, a card is simply placed in front of the mirror and raised to send a flash.