Definition of "semaphore"

We must here take the liberty of expostulating with Sir Home [Riggs] Popham and the first Lord of the Admiralty, for having given to the telegraphic machine, invented by that gallant officer, the barbarous name of Semaphore, instead of Sematophore or Semophore—either of them ugly enough.]

constructus. Editio nova, auctior et emendatior. Vol. I. Partes I–IV. Londini, in ædibus Valpianis, 1815–1818. [book review]”, in William Gifford, editor, The Quarterly Review, volume XXII, number XLIV, London: John Murray, […], page 342

The large Silver Medal of the Society was this Session voted to Nic[h]olas Harris Nicolas, Esq. of the Inner Temple, for an Improvement on the Vertical Semaphore, and for his method of adapting a shifting Key to Telegraphic Communications, for the purpose of insuring their Secrecy. A Model of Mr. N's Semaphore has been placed in the Repository of the Society.

1821, “[Papers in Mechanics.] No. V. Improved Semaphore.”, in Transactions of the Society, Instituted at London, for the Encouragement of Arts, Manufactures, and Commerce; […], volume XXXIX, London: Sold by the housekeeper, at the Society’s House, […]; printed by T[homas] C[urson] Hansard, […], page 104

That the systems of telegraph and semaphore now in use are in a great measure use-less by night, and totally so in a fog, cannot be doubted; and that a mode, both rapid and secret, would could be put into practice at small expense, in fact little more than the first cost, would be of essential utility to the Government of the country adopting it, is equally true.

1831 October 8, W. Thomas, “[General Correspondence.] Night Signals.”, in The United Service Journal, and Naval and Military Magazine, part III, number 35, London: Henry Colburn and Richard Bentley, […], page 392

The arms of the semaphore at the settlement were, in fact, gesticulating with comical vehemence.

1875, Marcus Clarke, “Running the Gauntlet”, in His Natural Life [For the Term of His Natural Life], volume III, London: Richard Bentley and Son, page 27

When, on long lines of stations, towers or other structures are used, it may be necessary, for greater speed, to sometimes employ semaphores for aerial telegraphy. [...] Semaphores consist of a post with arms. The arms starting with about three feet in length, to be increased one foot for every mile. These arms are made movable by ropes passing over wheels or pulleys, and moved by a crank below.

1879, Albert J[ames] Myer, “Semaphores”, in A Manual of Signals for the Use of Signal Officers in the Field, […], Washington, D.C.: Government Printing Office, pages 193–194

And so they went down, Jim steering by his father, turn for turn, over the Mayapur Bar, with the semaphores on each bank duly signalling the depth of water, [...]

1895 January–June, Rudyard Kipling, “An Unqualified Pilot”, in Land & Sea Tales for Scouts and Guides, Bombay: The Gresham Publishing Company; London: Macmillan and Co., published August 1919, page 68

It is essentially an emergency device, primarily for use on single track railroads, and is intended to place the control of semaphores at the several stations under the control of the dispatcher. By means of this signal the dispatcher may throw a semaphore to "stop position" at any desired point, regardless of the condition of the operator's instrument at that station, that is whether or not the key of his instrument on the dispatcher's wire is open.

1906 July 19, “The Wright Telegraph Railroad Signal”, in The Iron Age, volume LXXVIII, New York, N.Y.: David Williams Company […], page 139, column 2

Now, a century later, semaphores and discs are giving place to colour and position lights. What will be the fashion in 2041? Universal continuous cab signalling?

1941 April, “Centenary of the Semaphore Signal”, in Railway Magazine, page 171

Travelling by the rural tramway was quite an experience; the small car would bounce about on the bad track like a ship in a rough sea; at some places, there would even be genuine railway semaphore signals controlling the trams.

1968, F[rits] van der Gragt, Europe's Greatest Tramway Network: Tramways in the Rhein–Ruhr Area of Germany (Uitgaven van de Nederlandsche Vereeniging van Belangstellenden in het Spoor- en Tramwegwezen [Publications by the Dutch Association of People Interested in the Rail- and Tramway System]; 4), Leiden: E[vert] J[an] Brill, page 128

Innovations in the communications industry often means that existing media become obsolete. There are no semaphores any longer. (Semaphores were used by the French revolutionary armies in the late 1790's to relay information to Paris about their victories in the Savoy.)

1995, Sten Thore, “Messages, Images, and Robots”, in The Diversity, Complexity, and Evolution of High Tech Capitalism, Boston, Mass., Dordrecht: Kluwer Academic Publishers, page 27

He had got used to the clacks towers now. Sometimes it seemed as though every roof sprouted one. Most were the new shutter boxes installed by the Grand Trunk Company, but old-fashioned arm semaphores and even signal flags were still well in evidence.

2004 September 25, Terry Pratchett, Going Postal (A Discworld Novel; 33), London: Doubleday; republished London: Corgi Books, Transworld Publishers, 2005 (2014 printing), pages 149–150

Even so, there are only four others in my car after leaving the pretty station at Abergavenny, a haven of old GWR semaphores.

2020 December 2, Paul Bigland, “My weirdest and wackiest Rover yet”, in Rail, page 67

Its [the article's] object is to furnish a rule for determining the number of distinct signals which can be made by any semaphore, whatever be the number of arms or indicators, of whatever be the number of positions of each arm. In the Cyclopædia of Rees, the number of signals which the semaphores of the line of communication between Paris and Landau were capable of making, is stated to be 823,543, which is no less than 1,274,608 fewer than the real number, an error not arising from the press, but from the principle of computation.

1834 October, Charles Blackburn, “XXXV. A Method of Determining the Number of Signals which Can be Made by the Modern Telegraphs.”, in David Brewster, Richard Taylor, Richard Phillips, editors, The London and Edinburgh Philosophical Magazine and Journal of Science, volume V (Third Series), number 28, London: Printed by Richard Taylor, […], printer to the University of London; sold by Longman, Rees, Orme, Brown, Green, and Longman; [et al.], page 241

Buried treasures are naturally among the problems which have come to Mr. [Sherlock] Holmes. One genuine case was accompanied by a diagram here reproduced. [...] Each Indiaman in those days had its own semaphore code, and it is conjectured that the three marks upon the left are signals from a three-armed semaphore.

1924 September, Arthur Conan Doyle, “Sidelights on Sherlock Holmes”, in Memories and Adventures, Boston, Mass.: Little, Brown, and Company, page 110

A system of communication called semaphore uses flags or flashing lights to send messages over distances. [...] Code flags are less common today but are sometimes used by ships that have lost radio contact.

2006, Erinn Banting, Inventing the Telephone (Breakthrough Inventions), New York, N.Y., Toronto, Ont.: Crabtree Publishing Company, page 5, column 2

As always in Lisbon, my heart throbbed semaphores to call Tónio.

2008, Katherine Vaz, “Lisbon Story”, in Our Lady of the Artichokes: And Other Portuguese-American Stories, Lincoln, Neb., London: University of Nebraska Press, page 115

Consider the wagging tail, the most basic semaphore in dog/human communication.

2008, Gene Weingarten, “Remembering Harry”, in Old Dogs are the Best Dogs, New York, N.Y.: Simon & Schuster, page 4

Semaphore—a system of communicating over long distances by holding the arms or two flags in certain positions—is not a very efficient mode of communication for us. But for the Panamanian golden frog, semaphore is just the ticket. These frogs live near waterfalls, where the constant din renders vocal communication useless. [...] When they want to get someone else's attention, they flash pale patches of skin on their limbs or the webs between their toes.

2010, Jonathan Balcombe, “Communicating”, in Second Nature: The Inner Lives of Animals, New York, N.Y.: St. Martin’s Press, part II (Coexistence), page 84

For a half-hour episode, "The Long Shadow" was unusually complex, a web spun out of deception and equivocation that untangles when [Ronald] Reagan, transmitting his customized semaphores of concern (ridged brow, pursed lips, pained eyes), divulges the truth: [...]

2014, Bernard F. Dick, “Worlds Elsewhere”, in The President’s Ladies: Jane Wyman and Nancy Davis, Jackson, Miss.: University Press of Mississippi, page 215

Several synchronization techniques have been proposed and many of them have been adopted by parallel and distributed operating systems or parallel programming platforms. [...] Semaphores represent another synchronization technique that is mainly used by traditional stand-alone operating systems.

1996, P. Theodoropoulos, G. Manis, P. Tsanakas, G. Papakonstantinou, “Extending Synchronization PVM Mechanisms”, in Arndt Bode, Jack Dongarra, Thomas Ludwig, Vaidy Sunderam, editors, Parallel Virtual Machine – EuroPVM ’96: Third European PVM Conference, Munich, Germany, October 7–9, 1996: Proceedings (Lecture Notes in Computer Science; 1156), Berlin, Heidelberg: Springer-Verlag, page 315

A semaphore makes sure that the different processes don't step on each other's toes when they access the shared memory segment. Before a process can use the segment, it needs to get control of the semaphore. When it's done with the segment, it releases the semaphore for another process to grab.

2003, David Sklar, Adam Trachtenberg, “Variables”, in Paula Ferguson, editor, PHP Cookbook, Sebastopol, Calif.: O’Reilly & Associates, section 5.6 (Sharing Variables across Processes), page 124

It is up to the programmer to ensure that if one thread updates multiple dependent memory locations (for example, writing a string, or updating a table) that another thread might read, some protection is put in place to ensure that the two threads don't update and read at the same time. [...] Several techniques are used by programmers to prevent this, including locks, semaphores, and mutexes.

2012, Timothy Mangan, “L1/L2/L3 Memory Cache”, in Windows System Performance through Caching: 15 Ways Caching Improves System Performance (Inside the OS Series), Canton, Mass.: TMurgent Technologies, page 22

The person intending to Semaphore will make the International Code Signal VOX (I am going to Semaphore to you), and set his Semaphore at the alphabetical sign [...] with the Indicator out, and wait until the person to whom the Semaphore signal is to be made hoists his answering pennant close up. [...] The British method of Semaphoring by flags held in the hand which is shown in plate VIII is exactly the same as the British Movable Semaphore system, which has just been explained, the positions of the apparatus which denote the letters, numbers, and special signs being, it will be seen, identical in each case, and the only difference being in the apparatus employed.

1907, United States Hydrographic Office, “Distant Signals”, in International Code of Signals, American edition, Washington, D.C.: Government Printing Office, part III, page 539

These gunny-sack chaps are not animals or savages. Look, Henry! They are semaphoring! See that tree there, and that big one across the cañon. Watch the branches wave.

1920 September, Jack London, chapter X, in Hearts of Three, New York, N.Y.: The Macmillan Company, page 137

Minutes later, unseen by the defenders, he semaphored back across the valley that he was going to make a fresh attempt.

1990, Peter Hopkirk, “The Climactic Years”, in The Great Game: On Secret Service in High Asia, London: John Murray; republished Oxford, Oxfordshire: Oxford University Press, 2001, page 478

Near the concession stand on the east side of the park, she saw two familiar figures sitting on a bench in the shade of a large oak. Her father hailed her, wildly semaphoring with his hot dog.

2008, Elizabeth Elwood, “Gilda Died for Love”, in A Black Tie Affair: And Other Mystery Stories, Lincoln, Neb.: iUniverse, page 113

He can't hear what they're saying, but Jake is making angry movements with his hands and his taut posture semaphores, even to Daniel, his distinct displeasure.

2011, Heather Menzies Jones, chapter 25, in NanoMan, [Morrisville, N.C.]: Lulu.com, page 133

[Barack] Obama doesn't merely evince blackness; he uses his blackness to signal and court African Americans, semaphoring in a cultural dialect of our creation—crooning Al Green at the Apollo, name-checking Young Jeezy, regularly appearing on the cover of black magazines, weighing the merits of Jay-Z versus Kanye West, being photographed in the White House with a little black boy touching his hair.

2012 September, Ta-Nehisi Coates, “Fear of a Black President”, in James Bennet, editor, The Atlantic‎, Washington, D.C.: The Atlantic Monthly Group, archived from the original on 3 January 2020