Nersac: Un Poste Optique (Zoom)
This 1910s French Postcard is NOT my work, but I believe it in the public domain in the US as a work published prior to 1923.
This is a closeup zoom of the apparatus shown in my French postcard, postmarked 1905, showing French military telegraphists with the their visual telegraph, the "Mangin Apparatus", that served as a heliograph in sunlight, and a signal lamp at night or under clouds. I've also posted a cross-sectional diagram and the full front scan of the postcard.
A 1913 French article on this, and other types of French, English and American heliographs may be found here: gallica.bnf.fr/ark:/12148/bpt6k65514029/f351.image.r=lese...
I claim no copyright on this, you may use it as your laws allow. Attribution is not required, but a link back to this page would be appreciated.