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Home , Claude Chappe, Optical telegraph, Semaphore, The Victorian Internet

NG07.indb 44 7/30/15 9:23 PM Choreographies of Information The Architectural of the Eighteenth Century’s Optical

Dimitris Papanikolaou

Today, with the dominance of digital information and to communicate the of Troy’s fall to Mycenae. In technologies (ICTs), information is 150 BCE, Greek historian Polybius described a system of mostly perceived as digital bits of electric pulses, while sending pre-encoded with torches combina- the Internet is seen as a gigantic network of cables, rout- tions.01 And in 1453, Nicolo Barbaro mentioned in his ers, and data centers that interconnects cities and con- diary how Constantinople’s bell-tower network alerted tinents. But few know that for a brief period in history, citizens in real time to the tragic progress of the siege before electricity was utilized and information theory for- by the Ottomans.02 It wasn’t until the mid-eighteenth malized, a mechanical version of what we call “Internet” century, however, that developed connected cities across rural areas and landscapes in into vast territorial networks that used visual Europe, the , and Australia, communicating and control protocols to disassemble any into 045 information by transforming a rather peculiar medium: discrete signs, route them wirelessly through relay sta- geometric architectural form. tions, reassemble them at the destination, and refor- mulate the message by mapping them into words and The Origins of Territorial Intelligence phrases through lookup tables. And all of this was done was not a novelty in the eighteenth in unprecedented speeds. Two inventions made it pos- century. Early data networks communicated intelligence sible: the telescope and the . across land and sea through such media as fire, sound, The telescope’s invention in 1608 improved telecom- light, pigeons, , and . In the twelfth cen- munications as nothing else before. With a thirtyfold tury BCE, for example, Agamemnon used a bonfire relay magnifying power, telescopes expanded line across six hundred kilometers of ocean and terrain links more than an order of magnitude, while dropping

NG07.indb 45 7/30/15 9:23 PM dramatically their infrastructure and operational costs.03 remained the same: form follows information. Over the Optical telegraphs were mechanically transformable years two designs prevailed: the and the structures—partly buildings, partly machines—that shutter telegraph. could reconfigure their silhouettes to visually manifest The semaphore, invented in 1793 by Chappe, con- signs. Together with telescopes, they created a powerful sisted of a thirty-foot-high mast with a pivoting arm on mechanical internet that could automatically transmit top called the regulator. At the two ends of the regulator, any arbitrary message, independent of its length, through which measured fourteen feet long and thirteen inches a choreography of mechanical transformations. Through wide, there were two smaller rotating arms called the its brief history, the mechanical internet of optical teleg- indicators, which measured six feet long and one foot raphy introduced fundamental concepts of communica- wide each. Chappe found through experiments that their tion and computing like error detection, data compaction, thin silhouettes were easily distinguishable from large , encryption, handshaking, clock synchroni- distances. Both the regulator and the indicators could zation, restoration, , regulation and even rotate in forty-five-degree intervals: the regulator could fraud that are all present today on the Internet. take four positions (horizontal, vertical, and the two diag- The contribution of this essay is twofold: on the one onals), while each indicator could take eight positions. hand, it sheds light to the techno-sociopolitical context The apparatus, which was painted black to contrast with of the history of optical telegraphy, a topic that is largely the blue sky, could take a total of 256 (eight by eight by disregarded in architectural and urban history; on the two) different positions, or eight bits of information stor- other hand, it makes three thesis statements on the rela- age. Not all positions were retained, however: Chappe tion of optical telegraphy to the contemporary critical eliminated the positions in which the two indicators were discourse on architecture, media, and urban intelligence. parallel to the regulator and pointed inward because they were hidden. Furthermore, from the four positions of the The Architectural Internet regulator, he only kept the vertical and horizontal ones. In March 1791, , a French cleric and inven- After eliminating a few other positions, the semaphore tor, placed with his brother two synchronized pendulums telegraph eventually encoded a total of ninety-two signs.05 with ten signs each on their clock faces several hundred The shutter telegraph, first invented in 1794 by the meters apart. His goal was to send a message as a combi- Swedish baron Abraham Niclas Edelcrantz and modi- nation of signs across the two devices. fied in 1796 by the British lord George Murray, utilized a To send a sign, the transmitting clock emitted a sound of flipping shutters, pivoted on horizontal axes, precisely at the moment when the indicators of both that could open and close individually. Edelcrantz’s clocks passed from the specific sign. By combining signs, apparatus had ten shutters organized in a three-by- predetermined messages could be found in a dictionary.04 three matrix, with a tenth shutter mounted on top of the The solution, however, was cumbersome, mechanically middle column. It could encode 1,024 signs, or ten bits. complex, and operationally complicated. Two years later, Murray’s apparatus used only six shutters, organized in a Chappe came up with a new idea, conceptually, mechani- two-by-three matrix, with a capacity of sixty-four differ- cally, and operationally simpler: one mechanically trans- ent alphanumerical characters or six bits. Like Chappe, formable structure configured its silhouette to visually both Edelcrantz and Murray optimized the design of their represent a sign; then, it waited for the remote structure devices through experimentations. Edelcrantz found that to replicate the silhouette, thus confirming the sign. By the gap between shutters needed to equal the width of placing the devices on high enough towers, the sky could one shutter, at the least, to prevent the human eye from 046 be used as a bright background to visually enhance the mistakenly blending adjacent shutters when viewing silhouettes. Relay cascades could transmit messages by the apparatus from a great distance. He also determined copying each other’s silhouette through a domino effect. the size and angle of the matrix as a function of the dis- Chappe named his invention “telegraphy” from the Greek tance the towers had between them, the magnitude of words tele (distant) and graph (writing). An architectural the telescope used, and the minimum visual angle of a form of communication had just been invented. human eye.06 Likewise, Murray standardized the design of his matrix on two supporting posts twenty feet high The Signaling Apparatus: Form Follows Information and twelve feet apart; each shutter was roughly six feet The evolution of optical telegraphy was an interplay by five feet in size.07 between communication protocols, engineering ingenu- ity, operational simplicity, and cost. The concept though Opposite: Chappe semaphore.

NG07—Geographies of Information

NG07.indb 46 7/30/15 9:23 PM 047

Dimitris Papanikolaou

NG07.indb 47 7/30/15 9:23 PM 048

NG07—Geographies of Information

NG07.indb 48 7/30/15 9:23 PM The Control Room and the Operators: apparatus, if the telescope and control mechanism were The Puppeteers located close enough to each other.09 Operators repli- Optical telegraphs were remotely linked to an interface cated signs without knowing how to interpret them. Only that a human operator could manipulate inside a con- authorized officers with frequently updated codebooks trol room. Chappe’s device was mechanically connected could interpret signs. This knowledge separation decoupled through pulleys, disks, gears, belts, and cables to a min- operations from intelligence, enhancing security through- iature replica of the device inside that room. Likewise, out the entire . Edelcrantz’s and Murray’s signaling devices each linked through strings to a small control box with ten rings, The Building Typology: The Mechanical Puppet which the operator could pull with his fingers. Like In dense urban environments, optical telegraphs were puppeteers, operators could manipulate the miniature often placed on top of high-rise public buildings, like devices inside the control room, and the large appara- churches, town halls, or bell towers. In rural areas, how- tuses atop the tower would silently replicate the pos- ever, optical telegraphs developed their own typologies tures. Edelcrantz developed an even more sophisticated in which the signaling apparatuses were architectur- mechanism that used foot pedals to control the shutters, ally integrated to the building. These typologies evolved leaving the hands of the operator free to turn the pages based on available materials, human factors, and com- of the codebook.08 munication protocols. Towers were built out of timber Inside the control room, telescopes mounted on the or masonry and were often fortified, as they constituted walls pointed to the apparatuses of the nearby telegraph military targets. They often contained a kitchen, bed- towers. Each relay tower had three to four operators: two room, storage for food and fuel supplies, and external 049 watchmen, who monitored nearby towers for incoming water well.10 Their design typically employed simple or outgoing , and a third (and occasionally fourth) geometries such as rectangular or cylindrical prisms; worker who operated the apparatus to transmit signals. however, more complicated types existed. T. W. Holmes, A terminal station had only two operators, as it only con- for example, mentions four building typologies in the nected to one nearby tower. Occasionally, a single highly British system: a bungalow and three-, four-, and five- skilled worker could both watch and manipulate the story types. Selection was based on the tower’s location and the size of the operator’s family. Typologies, however, depended also on the landscape and . Opposite: Swedish shutter telegraph system. Above, left: The Furusud shutter telegraph in . Above, right: Inside an In his treatise, Edelcrantz explains that on the plains or operator’s room at the Furunsud telegraph. in flat landscapes telegraphs need to be positioned above

Dimitris Papanikolaou

NG07.indb 49 7/30/15 9:23 PM HASTE BANNICLE PEWLEY CHATLEY

to HOLDER to COOPERS

the level of fog, mist, or any mirage effects of the hot sea- systems. In Chappe’s system, each transmission con- son, using the sky as much as possible as a background.11 sisted of two consecutive signs, the first pointing to a Furthermore, he determined the distance of towers as page and the second pointing to an entry in that page. a function of the curvature of the earth, mirage effects, Chappe’s codebook had ninety-two pages of ninety-two and natural geography of the landscape. The height of entries each, for a total of 8,464 predefined messages. Hol- the control room and the signaling apparatus in the tow- zmann estimated that Chappe’s telegraph was capable of ers varied based on the location and the height of nearby sending up to twenty characters per minute,14 an aston- trees or other obstacles, resulting in each tower having a ishing rate compared to the twenty-five characters per different architectural configuration. minute of the first electromagnetic telegraph in 1837.15 Edelcrantz’s system also used a lookup table with 1,024 Transmission: Form Follows Form entries. To map his device’s configurations to index num- Relay towers transmitted data by copying each other’s bers he came up with the following: from top to bottom, form in a domino effect. Hence, form followed form at he assigned the values 1, 2, and 4 to the shutters of each its most literal sense. Transmission speeds were remark- of the three columns. Then, for each column, he added ably high. According to Edelcrantz, Chappe’s device could the values of the closed shutters producing a triplet of manually change position every twenty seconds, sending octal numbers ranging from zero to seven. The complete approximately two to three signs per minute.12 Assuming for each signal consisted of the three numbers, pre- the device utilized 128 of its total 256 signs, this would be fixed by letter A if the tenth large shutter was closed. For equivalent to a transmission speed of 0.5 bits per second. example, code A636 meant a configuration in which the Edelcrantz’s ten-bit code could change every eight to ten top two shutters of the middle column, the bottom two seconds, while Murray’s six-bit code could change every shutters of the first and third columns, and the tenth five seconds, both giving a signaling speed of approxi- shutter were closed. Murray’s system was simpler: with mately one bit per second.13 With that speed, a message a limited range of only sixty-four entries, it was based on could traverse the 120 stations of the – line in explicit spelling. less than twelve minutes. Optical telegraphs developed sophisticated protocols 050 Although signs were transmitted at the aforemen- for communication, addressing, and error detection that tioned speeds, their information content depended on are found today in modern telecommunication systems. how they were utilized to construct messages. Two meth- In the French system, for example, only terminal sta- ods were used: in the first, signs pointed to predefined tions could send or receive messages while all other sta- sentences in lookup codebooks; in the second, signs tions served as relays. In the Swedish network, however, pointed to alphanumeric characters used for explicitly any station could send or receive messages to or from spelling out messages. While the second method was any other station. This addressing detail affected the admittedly slower, it was also logistically simpler and cheaper as it did not rely on voluminous dictionaries that Above: Heights of operator room and semaphore apparatus were updated and reprinted often. in relation to landscape topography and tree height. A por- Both Chappe and Edelcrantz used codebooks in their tion of the semaphore line in England.

NG07—Geographies of Information

NG07.indb 50 7/30/15 9:23 PM Dunkerque Anvers Calais Bruxelles Boulogne

Mayer Cherbourg Eu

Metz Chalons Dreux Brest Paris Avranches St. Brieux Saint -Malo Luneville

Rennes Nantes Huningue

Dijon Besancon Nantes

Chalons- sur-Saone Poitiers

Lyon Angouleme Blaye Turin

Valence

Agen Nimes Avignon Toulouse Montpellier Bayonne Behobie Toulon Narbonne

Perpignan

100 km

60 mi

format, size, and eventually transmission speed of the could affect the entire line. As telegraphs had only a messages as in the former case the messages did not front and a back facade, they could be read only from a include recipient or information while in the lat- certain viewing angle, which restricted how towers could ter case they did.16 Special regulations were invented to be placed. In , a trial period of one year typically deal with message traffic, which was bidirectional and existed for new stations: during this time, stations were often heavy. When traffic accumulated in a station, for often moved around until a good location was found.18 example, rules prioritized which message to switch and By the early nineteenth century, optical telegraphy which one to hold, especially in hubs. As networks grew, networks in Europe were vast and busy. More than a thou- so did their complexity, vulnerability, and ingenuity. Both sand telegraphs connected cities from Paris to Perpignan Chappe and Edelcrantz knew that their system would be and Toulon in the south, to Amsterdam in the north, to as strong as its weakest link: a single error in one relay Brest in the west, and to Venice in the east, streaming station could shut down an entire line. Self-reporting information at full capacity. In France, for example, traf- mechanisms identified problematic nodes in the net- fic averaged several hundred messages per year, serving 051 work: towers kept logs and reported their peer towers if mostly military, governmental, and stock or commodity they were slow in responding. Penalties included fines market purposes.19 The Paris–Lille line was completed and imprisonment.17 in 1794, with the first official message sent from Lille to Paris on August 15. Geographies of Information Telegraph relay towers were erected at eight- to fifteen- Above, left: The Chappe network in France, showing major kilometer intervals across the landscape, creating net- cities. Above, right: Axonometric drawing illustrating how the Chappe mechanism worked. Colors indicate the individual works of various topologies. The location of each tower pulley systems for manipulating the device. The blue bar was of paramount importance to the reliability of the controls the regulator while the green and red handles con- network: even one misplaced or problematic station trol the left and right indicators.

Dimitris Papanikolaou

NG07.indb 51 7/30/15 9:23 PM Optical telegraphy operated in France from 1794 to Sociopolitical Context 1855, growing gradually and steadily. In 1816, a line was In the midst of the in Europe (1803– constructed from Paris to Calais. In 1821, a new line 1815), the majority of optical telegraphy networks were connected to Toulon. Two years later, Paris con- developed, operated, and maintained almost exclusively nected to Bordeaux, while in 1828 Avignon connected to by governmental authorities for diplomatic and military Perpignan. By 1852, the network reached its peak with purposes. As war and funding came to an end, telegraphs 556 stations and more than 4,800 kilometers of relay found new applications where time-sensitive informa- line serving twenty-nine of France’s largest cities. All of tion had to travel faster than material resources. Such these lines were operated and maintained by the French applications included trading stocks and commodities in Ministry of War,20 and employed more than three thou- financial markets or operating steam-powered trains in sand workers.21 rapidly expanding railway networks. Similar networks connected other European coun- The new technology was not always embraced by tries. In 1801, Sweden had four operating lines connect- the public. Like most communication media, optical ing to Fredriksborg, Grisslehamn, Signilskär, telegraphs and their buildings symbolized instruments Helsing­borg, and Eckerö, while in 1809, its network of governmental authority, control, surveillance, con- ex­pand­ed to fifty stations linking Gävle and Landsort. In spiracy, and oppression. In Chappe’s early experiments, the , by 1808, the British Admiralty had a some believed he was trying to communicate with the 052 network of sixty-five stations that could send messages Austrians and Prussians.24 Later, during the upheaval form to Deal, on the English Channel, in about one of the , many telegraph towers were minute.22 Soon networks expanded in the rest of Europe, burned and torn down with their operators nearly saving connecting cities in Norway, Finland, Denmark, the Neth- their lives from the mobs. erlands, Germany, and , as well as on the East Coast Despite overall skepticism, optical telegraphs consti- of the United States and in Australia.23 Although optical tuted also technological achievements of wonder, admi- telegraphy networks covered large areas in Europe, most ration, and envy. Many inventors claimed ownership of national networks were incompatible and fragmented. the new invention and the patent war among them was Having different communication protocols and signaling fierce. As Edelcrantz wrote in his treatise, mechanisms, there was often no means for information to smoothly flow from one system to another. Above: British admiralty shutter telegraph building.

NG07—Geographies of Information

NG07.indb 52 7/30/15 9:23 PM A B C D E F G H I J

K L M N O P Q R S T

U V W X Y Z word end of space message

It often happens, with regard to new inventions, that The Eighteenth Century’s Smart Cites one part of the general public finds them use-less First, optical telegraphy networks constituted cybernetic prede- and another part considers them to be impossible. cessors of smart cities. In his book ME++, William Mitchell When it becomes clear that the possibility and the portrays the urban condition of the twenty-first century usefulness can no longer be denied, most agree that as an intelligent, networked landscape that uses elec- the whole thing was fairly easy to discover and that tronic nervous systems to serve the needs of its users they knew about it all along.25 in more efficient and sustainable ways.26 It is fair to say The extraordinary maintenance costs, the political insta- that nearly two centuries ago, optical telegraphy created bility, and the rapid technological advancement of Samuel a mechanical nervous system with a similar rhetoric F. B. Morse’s electric telegraph seized optical telegraphy but a more tangible implementation. Optical telegraph and its nascent architecture permanently in 1844. It lasted networks merged synergistically human operators, fifty years and it was the fastest and most reliable com- mechanical interfaces, and telescopes with decision munication system ever conceived until then. makers and financial institutions, creating self-regulating cybernetic systems with urban-scale feedback loops.27 Three Theses on the Architectural Internet Brokers in Paris could arbitrage from rising trading prices of Optical Telegraphy in Amsterdam in a matter of minutes. Train stations could Little is known about the architecture of optical tele- inform awaiting passengers of the imminent delay of an graphs. Within only fifty years from their first implemen- arriving train in nearly real time. Military commanders 053 tation until their replacement by the electric telegraph, could organize their army and fleet in response to enemy’s optical telegraphs remained partly machines, partly tactics. And corporate businessmen could send frequent buildings never managing to develop a mature architec- optical mails, or “omails,” to arrange time-sensitive deals. tural typology. Through their short evolution, though, they demonstrated a remarkably novel concept: that Form as a Medium of Information abstract architectural can semantically con- Second, information was manifested through abstract archi- struct and mediate urban intelligence. After portraying tectural language, both the control and interpretation of which their techno-sociopolitical context from an architectural were critical in closing the feedback loop of intelligence. While perspective, I conclude with three theses. Above: The British admiralty code.

Dimitris Papanikolaou

NG07.indb 53 7/30/15 9:23 PM Diagram illustrating how the British shutter telegraph worked.

3 1 Watchman 2 con rms Watchman 1 observes that next tower for incoming signals replicated signal

2

Operator replicates signal with the apparatus

in Mitchell’s rhetoric intelligence is mediated through Form as a Manifestation of Computation digital bits, in Chappe’s, Edelcrantz’s, and Murray’s it Third, optical telegraphs were early manifestations of archi- was mediated through physical space and geometry. tectural computing automata. Through their reconfigurable This is not to argue that manipulating form is a better forms, optical telegraphs not only represented informa- medium than flipping digital bits. But in a contemporary tion bits but also stored them in their finite formalistic discourse on intelligent environments where materiality, states. Furthermore, by the highly mechanized process by information, and human perception seek new models for which human operators executed tasks without knowing 054 seamless integration, such rhetoric gives new directions their meaning, optical telegraphy introduced basic con- for critical exploration. cepts of computation in which routines, when followed Optical telegraphy illustrated both how form can medi- methodically, produce logical and consistent outcomes. ate information and how in turn communication require- With their strict procedural protocol of finite states ments can drive architectural, urbanistic, and planning and lookup tables, the constrained inputs and outputs decisions. On the one hand, it produced a self-referring, of their control rooms, and the separation of execution signifying, and performative (almost postmodern) archi- from interpretation, optical telegraph towers resemble tecture.28 On the other hand, its (almost modern) lan- urban manifestations of architectural Turing machines.30 guage—abstract and functionalistic—derived through No one knows where this technology, idea, and typology experiments instead of imitation. The form in this case would have been taken, had information and computa- was the medium, not the message.29 tion theory been known then.

NG07—Geographies of Information

NG07.indb 54 7/30/15 9:23 PM Optical telegraphy has often been coined as history’s in the history of communications has this term been more mechanical Internet, a term with an emphasis on the mech- literally implemented than in the eighteenth century’s anisms with which the telegraphic apparatuses worked. optical telegraphy networks. And nowhere in the history of Throughout this essay I favor architectural Internet as a new architecture has knowledge been most closely associated term with an emphasis on the medium through which with built form. In an architecturally mediated internet, intelligence was implemented. Information etymologically “form follows information” and “form follows form” would means giving shape to communicate knowledge. Nowhere probably be the two most succinct principles of essence.

Acknowledgments: The author would 14. Considering a rate of twenty char- 28. For an analysis on the role of archi- like to acknowledge Tekniska Museet acters per minute, about two to tectural language as a signifying in Stockholm and the Archives three words of ten characters each medium, see Charles Jencks, The and Special Collections at Harvard could be sent per minute. Language of Post-modern Architecture University for their generous help in 15. Holzmann and Pehrson, The Early (New York: Rizzoli, 1977). accessing their archive materials. History of Data Networks. 29. A paraphrase of Marshall 16. Ibid. McLuhan’s quote “the medium is 01. See Gerard J. Holzmann and Björn 17. Holmes, The Semaphore. the message”; McLuhan advocated Pehrson, The Early History of Data 18. Duane Koenig, “Telegraphs and the importance of media over the Networks (Los Alamitos, CA: IEEE Telegrams in Revolutionary France,” content it caries in shaping social Computer Society Press, 1995), 26–29. Scientific Monthly 59, no. 6 (December perception. While optical telegraphs 02. Nicolò Barbaro, Diary of the Siege of 1944): 431–37. used shape to construct content, Constantinople, 1453, trans. J. R. Jones 19. Holzmann and Pehrson, The Early their form was decontextual- (New York: Exposition Press, 1969). History of Data Networks, 75. ized from meaning. See Marshall 03. Holzmann and Pehrson, The Early 20. Koenig, “Telegraphs and Telegrams McLuhan, Understanding Media: History of Data Networks, 31–44. in Revolutionary France.” The Extensions of Man (New York: 04. Ibid., 51–53. 21. Gerard J. Holzmann and Björn McGraw-Hill, 1964). 05. For a thorough description of Pehrson, “The First Data Networks,” 30. Turing machines, formalized by Chappe’s device see M. Chappe Scientific American 270, no. 1 (1994): computer scientist Alan Turing, are (Ignace Urbain Jean), Histoire de la 124–29. hypothetical computing automata télégraphie (Paris: L’auteur, 1824). 22. Holzmann and Pehrson, The Early that compute by manipulat- 06. See Abraham Niclas Edelcrantz, “A History of Data Networks. ing strings of symbols through Treatise on Telegraphs” (1796), trans- 23. Tom Standage, : finite states and rule tables. For lated and republished in The Early The Remarkable Story of the Telegraph a thorough description see Alan History of Data Networks, 129–78. and the Nineteenth Century’s On-Line Mathison Turing, The Essential 07. T. W. Holmes, The Semaphore: The Pioneers (New York: Bloomsbury, Turing: Seminal Writings in Computing, Story of the Admiralty-to- 2014). Logic, Philosophy, Artificial Intelligence, Shutter Telegraph and Semaphore 24. Koenig, “Telegraphs and Telegrams and Artificial Life; Plus The Secrets of Lines, 1796 to 1847 (Ilfracombe, UK: in Revolutionary France.” Enigma (Oxford: Clarendon Press; Stockwell, 1983). 25. Edelcrantz, “A Treatise on New York: Oxford University Press, 08. Holzmann and Pehrson, The Early Telegraphs,” in The Early History of 2004). Data Networks, 129–78. History of Data Networks, 105. Image Credits 09. Holmes, The Semaphore. 26. See William J. Mitchell, Me++: The 047: Chappe (Ignace Urbain Jean), 10. Ibid. Cyborg Self and the Networked City Histoire de la télégraphie (Paris: L’auteur, 11. Holzmann and Pehrson, The Early (Cambridge, MA: MIT Press, 2003). 1824). History of Data Networks. 27. For an analysis of the synergies 12. Operators could change the device between human administration, 048, 049: Tekniska Museet, in one to two seconds, but they software, and hardware in applica- Stockholm. held each signal for twenty to thirty tions of optical telegraphy see 050: Illustration reproduced based on 055 seconds to ensure reception from Alexander J. Field, “French Optical Holmes, The Semaphore, 89. the remote towers. Telegraphy, 1793–1855: Hardware, Software, Administration,” 13. Gerard J. Holzmann, Design and Valida- 051–054: Illustrations by the author. tion of Computer Protocols (Englewood Technology and Culture 35, no. 2 (April Cliffs, NJ: Prentice Hall, 1991). 1994): 315–47.

Dimitris Papanikolaou

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