This section is from the book "The Home Cyclopedia Of General Information", by Charles Morris. Also available from Amazon: Home Cyclopedia of Necessary Knowledge.
[Gk.] A means of signaling invented by Chappe in 1793. Formerly in railway signaling there were three positions: at right angles meant stop; at half a right angle, go slowly; hanging down, that the line was clear. Nowadays semaphores have two positions: when the arm is up, danger ; when down, clear.
 
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