heliograph

The "mirror and disc" apparatus at the right is a 5" Mance heliograph. The heliograph was used to signal by Morse code using flashes of reflected sunlight created by tilting the mirror intermittently. This one is set up in the "duplex" (twin mirror) arrangement. The duplex configuration was used when the sun was on the opposite side of the signaller from the target. The leather carrying case dangling below the tripod by the shoulder strap was use to carry the parts atop the tripod for travel, and the tripod itself was slung over the shoulder by the strap attached to the left leg of the tripod, with the cylindrical cap at the end of the sling holding the legs of the tripod together. The disc dangling just above the case is a protective cap (with female threads) that protected the male threads atop the tripod. As noted at left, the heliograph saw little use during the trench warfare on the Western front in WWI, but rather more so in the mobile warfare towards the end. Another photograph of heliographs in use on the western front is this one at the Imperial War Museum: www.iwm.org.uk/collections/item/object/205072698 .For more information on heliographs, see the Wikipedia article on heliographs and its references.

British troops operating from Nordia Hotel building overlooking Jaffa Road and Barclays Bank, showing heliograph operator signaling to troops on Tower of David, Jerusalem, Palestine - circa 1938

Heliograph: The two tripods held by the two soldiers at right comprise a US Army Signal Corps heliograph - a tripod-mounted device for sending messages by flashes of sunlight using Morse or Myer code, with a range up 30 miles or so. This heliograph is set up in duplex, or "dual-mirror" mode, the mode used when the sun was behind the signalers. The job of the dark-suited soldier at the extreme right was to keep the sun beam reflected by the dual 4.5 inch square mirrors on his tripod in constant alignment on the target as the sun moved, using vernier elevation and azimuth screws. The job of the light-suited soldier in the middle was to open and close the shutter flap on his tripod to produce the dots and dashes of the code. A diagram showing this heliograph (albeit in single-mirror mode), taken from [1], is here (click on the thumbnail to magnify), and see [1] for the dual-mirror mode diagram. An 1893 photograph of this type of heliograph (albeit in single-mirror mode), taken from [2], is here (click on the thumbnail to magnify) To learn more about heliographs, you can read [1] and [2], as well as this Wikipedia article: en.wikipedia.org/wiki/Heliograph You can also see this Flickr gallery (click on the thumbnail): [http://www.flickr.com/photos/signalmirror/galleries/72157630246445306/] and this set (click on the thumbnail) : (Historical Photographs of American Heliographs) [http://www.flickr.com/photos/signalmirror/sets/72157631040759962/] [ 1 ] Annual Report of the Chief Signal Officer of the Army to the Secretary of War for the Year 1888, Government Printing Office, 1889 The new standard heliograph is discussed in Appendix I, pp. 42-47, and depicted on page 46, here: books.google.com/books?id=E2nPAAAAMAAJ&pg=PA46&dq... [2] "The Heliograph", The Compass, Vol. II, No. 11, June 1, 1893, page 161 books.google.com/books?id=tX0SAAAAYAAJ&pg=PA161

signal mirror Thanks for the great information!

There are two heliographs visible - one towards the front, and one further back. I think this is one panel of a stereograph - the sterograph is here at the National Galleries of Scotland:
www.nationalgalleries.org/art-and-artists/80944/heliograp...

It is very hard to tell from this photo, but I think the angle between the heliograph rear rod and the mirror is too large for the heliograph to be the British Mance pattern (right example in image below), and is rather than India pattern (left example in image below), as one might expect from Indian troops in WWI.