Heliograph mirror
Item
Title
Heliograph mirror
Description
square Heliograph mirror with foresight attached with string and instructions on reverse includes cotton cover with flap instructions are as follows: 1. Hold the foresight in the left hand in line with the target about 6 inches in front of the eye 2. Place the back of the mirror immediately in front of the eye with the right hand and align the two holes on the target 3. Rock the mirror until the scribed circles appear on the foresight and the black spot centralizes on the foresight hole. The beam is then directed on to the target. 4. The beam need not be rocked deliberately as the hand does this inadvertently.
Identifier
009.016.014
Format
Provenance
A Heliograph is a mirrored communications device for sending messages in Morse Code by flashing reflected sun's rays to a distant station. As a "rule of thumb" the range of a heliograph is ten miles per inch of the mirror’s diameter. Therefore, a 5" mirror, whether round or square, would have a range of about 50 miles, the 1.8" mirror of about 18 miles. The diameter of the reflected flash of a flat mirror is about 49 feet per mile, independent of the mirror’s size or shape, however, the larger the mirror the brighter the image. Therefore, the beam width at ten miles would be about 500', at fifty miles it would be about 2,500', or about 1,250' on either side of (or above and below) the targeted station if perfectly centered. It is essential to maintain regular adjustments of the sun mirror to compensate for the apparent movement of the sun. The projected image is round regardless of the mirror's shape, it of course being that of the reflected sun.
Abstract
Good
Date Created
unknown