Signal mirror (heliograph)
The light signaling device for transmitting the reflection of sunlight (super-bright "sunshine") is called a heliograph. With this device, a person in an extreme situation on land or on water can easily transmit a signal over considerable distances.
Reflections transmitted by the heliograph can be transmitted over very long distances in optimal weather conditions - on average 25-50 km. And on clear nights with a full moon, it is possible to transmit signals by reflecting the light of the moon.
The & nbsp; heliograph & nbsp; is made in the form of a small book (about 8x5 cm) from two plates, fastened together with a hinge. One plate is chrome-plated and polished on both sides, the other plate is matt. The polished, mirrored part has a so-called sighting hole exactly in the center, the size of a match head.