I'm a historian. I've struck on a curiosity about telecommunication technology in pre-modern times. I've read about a number of methods, and I'd like to ask some physics questions that got beyond my ken. This information is for my curiosity and creativity, not for any rigorous study, so I may be mentioning Wikipedia. Thank you for humoring me, and I hope I'm not asking too many questions :) I've now separated them into multiple threads by subject; this one ought to be about light. To conform with PF custom, I'll be adding the other questions to the threads after the first ones have been answered. Let anyone feel free to answer only those questions he prefers to. Light Signal beacons are really long established, as are smoke signals (inadvertant and otherwise). Heliography (flashing mirrors) and, later, semaphor towers were other low tech options. I'm certainly aware of the "hydraulic semaphor" of the ancient Mediterranean, but that's a mechanism for increasing the data in the transmission, where I'm curious about range. Q1. I wonder what range one would expect for fire/smoke visibility, assuming the message was simple.