Every Question, Logged
10 entries. Short answers first; links point to the panel with the detail.
What is optical signalling?
Sending information by something the receiver can see: moving arms, shutters, mirrors, lamps, lights or flags. It needs line of sight and a shared code.
Who built the first optical telegraph network?
Claude Chappe and his brothers in France. The first line, Paris to Lille, about 230 km, opened in 1794. Panel 01
Why did optical telegraphs disappear?
They failed in fog, rain and darkness, needed large crews and carried little traffic. The electric telegraph solved all three problems from the 1840s.
How far could a heliograph signal?
Typically 30 to 50 km in clear air. The US Signal Corps linked Mount Ellen, Utah, and Mount Uncompahgre, Colorado, about 295 km, in 1894. Panel 02
Are signal lamps still used?
Yes. Many ships carry signal lamps, the International Code of Signals keeps flashing-light Morse, and navies use lamps when radio silence matters.
What does Fl(3) W 15s mean on a chart?
A white light that shows a group of three flashes, repeating every 15 seconds. Panel 03
How many flags are in the International Code of Signals?
Forty: 26 letter flags, 10 numeral pennants, 3 substitutes and 1 answering pennant. Panel 04
What was the "England expects" signal?
Nelson's message flown from HMS Victory on 21 October 1805 before Trafalgar, sent in Popham's vocabulary code in twelve hoists.
Is flag semaphore still taught?
Yes, in some navies, sea cadet units and scouting groups, mainly as a backup skill and for training.
How reliable are the figures on this site?
Each figure is checked against at least two independent sources. Where sources disagree we give a range or the conservative value. Method
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