Semaphore line
A semaphore line is an installation used to send optical signals. It is also known as optical telegraph. Common system include signal towers with special installations on them or hand-held flags. The meaning of the signal is determined by the position of the elements, for example the flags. The signal can be read when it is in a stable position. In modern usage, it refers to signalling with a set of flags.
Signal towers came before the electric telegraph. They were faster than sending out post riders with the information.
Diagram of person holding 2 semaphore flags as letter "P"
Characters
The following semaphore characters are presented as one would face the flagman:
Rest / Space
Numerals
Error
Cancel
A / 1
B / 2
C / 3
Acknowledge
D / 4
E / 5
F / 6
G / 7
H / 8
I / 9
J
Letters
K / 0
L
M
N
Negative
O
P
Q
R
S
T
U
V
W
X
Y
Z
Related articles
Semaphore Line Media
Illustration of signalling by semaphore in 18th-century France. The operators would move the semaphore arms to successive positions to spell out text messages in semaphore code, and the people in the next tower would read them.
Illustration showing Robert Hooke's proposed system. At top are various symbols that might be used; ABCE indicates the frame, and D the screen behind which each of the symbols are hidden when not in use.
Sir Richard Lovell Edgeworth's proposed optical telegraph for use in Ireland. The rotational position of each one of the four indicators represented a number 1-7 (0 being "rest"), forming a four-digit number. The number stood for a particular word in a codebook.
19th-century demonstration of the semaphore
The Chappe Network in France
A replica of an optical telegraph in Stockholm, Sweden
Diagram of UK Murray six-shutter system, with shutter 6 in the horizontal position, and shutters 1–5 vertical
St. Albans High Street in 1807, showing the shutter telegraph on top of the city's Clock Tower. It was on the London to Great Yarmouth line.
