Visual Signals

Visual Signals - Flag Communication
'''This article explains the communication via flags, called "Flag Semaphore". Flag Semaphore is a system for conveying information at a distance by means of visual signals with hand-held flags, rods, disks, paddles, or occasionally bare or gloved hands. Information is encoded by the position of the flags; it is read when the flag is in a fixed position. Semaphores were adopted and widely used (with hand-held flags replacing the mechanical arms of shutter semaphores) in the maritime world in the early 1800s. Semaphore signals were used, for example, at the Battle of Trafalgar. This was the period in which the modern naval semaphore system was invented. This system uses hand-held flags. It is still used during underway replenishment at sea and is acceptable for emergency communication in daylight or, using lighted wands instead of flags, at night. Information is encoded by the position of the mechanical elements; it is read when the blade or flag is in a fixed position.'''

In modern usage it refers to a system of signaling using two handheld flags. Other forms of optical telegraphy include ship flags, Aldis lamps, and Heliographs. Semaphore lines preceded the electrical telegraph. They were faster than post riders for bringing a message over long distances, but far more expensive and less private than the electrical telegraph lines which would replace them. The distance that an optical telegraph can bridge is limited by geography and weather, thus in practical use, most optical telegraphs used lines of relay stations to bridge longer distances. Although passing mention of this idea had been made at many points in history, it was apparently the English scientist Robert Hooke who first gave a vivid and comprehensive outline of visual telegraphy to the Royal Society in a submission dated 1684; in it he outlined many practical details, but his system was never put into practice. Over a hundred years later a French engineer, Claude Chappe and his brothers took up the challenge again and succeeded to cover France with a network of 556 stations stretching a total distance of 4,800 kilometres. It was used for military and national communications until the 1850s.

Flag Semaphore System
Semaphores were adopted and widely used (with hand-held flags replacing the mechanical arms) in the maritime world in the early 1800s. The Semaphore flag signaling system is an alphabet signaling system based on the waving of a pair of hand-held flags in a particular pattern.

The flags are usually square, red and yellow, divided diagonally with the red portion in the upper hoist. The flags are held, arms extended, in various positions representing each of the letters of the alphabet. The pattern resembles a clock face divided into eight positions: up, down, out, high, low, for each of the left and right hands (LH and RH) six letters require the hand to be brought across the body so that both flags are on the same side.

Flag positions in Semaphore


One way to visualize the semaphore alphabet is in terms of circles: ·	first circle: A, B, C, D, E, F, G; ·	second circle: H, I, K, L, M, N (omitting J); ·	third circle: O, P, Q, R, S; ·	fourth circle: T, U, Y and 'annul'; ·	fifth circle: 'numeric', J (or 'alphabetic'), V; ·	sixth circle: W, X; ·	seventh circle: Z In there first circle, the letters A to C are made with the right arm, and E to G with the left, and D with either as convenient. In the second circle, the right arm is kept still at the letter A position and the left arm makes the movements; similarly in the remaining circles, the right arm remains fixed while the left arm moves. The arms are kept straight when changing from one position to another.

The Semaphore Alphabet


A and 1 (LH down RH low)



B and 2 (LH down; RH out)



C and 3 (LH down; RH high)



D and 4 (LH down; RH up - or LH up; RH down)



E and 5 (LH high; RH down)



F and 6 (LH out; RH down)



G and 7 (LH low; RH down)



H and 8 (LH across low; RH out)



I and 9 (LH across low; RH up)



J and 'alphabetic' (LH out ; RH up)



K and 0 zero (LH up; RH low)



L (LH high; RH low)



M (LH out; RH low)



N (LH low; RH low)



O (LH across high; RH out)



P (LH up; RH out)



Q (LH high; RH out)



R (LH out; RH out)



S (LH low; RH out)



T (LH up; RH high)



U (LH high; RH high)



V (LH low; RH up)



W (LH out; RH across high)



X (LH low; RH across high)



Y (LH out; RH high)



Z (LH out; RH across low)



Numerical sign (LH high; RH up)



Annul sign (LH low; RH high)



Error (LH and RH raised and lowered together)