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

The heliograph was used to signal using dots and dashes of reflected sunlight, and was used at ranges up to 20 miles and more. It consists of two tripods at center. The left tripod holds a mirror and a foresight to reflect and aim the light, and the right tripod a shutter to break up the reflected sunlight into dots and dashes. The thumbnail image below is a clickable link to a photo I took of a surviving example of this type of heliograph:

Seuss. The diagram you posted is of the 1888 model - some slight changes were made between that and the 1905 model shown here, though the parts and functions were, for the most part, the same. The big change was from the single-flap shutter to the six-blade shutter. Another change was the provision of azimuth adjustment screws on both ends of the mirror bar. The thumbnail below is a hyperlink to a 1913 advertisement for a model 1905 heliograph like the one in the Library of Congress photo:

The Library of Congress also holds a movie of a heliograph like that above in use by US Marines in 1915. The movie shows the heliograph being transported, set up, and operated. A copy is on YouTube, here:
www.youtube.com/watch?v=tdv11gZAUI8

The thumbnail below is a hyperlink to this still from that movie:

A modern video of a heliograph of the type in this LOC photo (operated by a complete beginner) is on YouTube here:
youtu.be/pBgH0Rz7kXY

Another from the May 1908 public field day at Governors Island. The PFC in front has the daytime signal flags. Behind him (and ready for "night work") is a Colt Acetylene Flash Lantern. The acetylene generator and carbide cannister is not yet connected. The signal flags are NOT semaphore flags (the poles are too long). They are used to send morse code. A long sweep overhead was a dash, a short sweep to one side was a dot.

4 of the 6 soldiers are in Signal Corps Uniform. The 2 on the right are in the uniform of the Coastal Artillery - the one in front showing the insignia of a second class gunner.

The tall sergeant in the rear wears the cap insignia and chevrons of a Master Signal Electrician. That flasher is NOT going to malfunction in front of all the VIPs.

No heliograph here, despite the "Tag". As Seuss. says, the displayed device is a signal lantern, specifically a Colt Acetylene Flash lantern, used primarily at night (hence the title at the top of the photograph: "Night Work".). The heliograph used mirrors to reflect sunlight, and were used during the day - there IS a heliograph on display in the accompanying photograph "Day Work", which can be viewed at the Library of Congress, here: www.loc.gov/item/2014680520/ This signal lantern ("Field Lantern" is depicted in Fig. 18 (page 111) of: Manual No. 6, Manual of Visual Signaling of the U.S. Signal Corps, by Captain D. J. Carr, Washington CPO 1905. The heliograph is depicted in Figures 8 & 9 (pp. 76 & 77) of that same manual. There was a Colt Acetylene Flash Lantern on display at the museum at Fort Huachuca, AZ, when I was there last. The 1905 manual gives the brightness of the field lantern as 1,900 candlepower (p. 112), vs. the millions of candlepower from the mirror-reflected sunlight of a heliograph.

Seuss. Here's a photo of a Colt Acetylene Flash Lantern on display at the Fort Gordon Museum. If you click on the thumbnail image below, then scroll down below the photo to the comments, you'll find links to more information about this device. Much of the material is in this thread:
www.treasurebunker.com/forums/index.php?/topic/3804-us-si...