The Early History of Data Networks by Gerard J. Holzman, Björn Pehrson

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1004 Book Reviews TECHNOLOGY AND CULTURE dom had difficulties obtaining the necessary loans at moderate inter­ est rates. Local savings banks were generally very keen to assist town councils in financing gasworks. In the late 19th century, financial markets in other Nordic countries were less developed and Ending capital was thus more complicated there than in prosperous Den­ mark. Furthermore, Denmark was at the time the most urbanized of the Nordic countries, and the construction of gas networks was less ex­ pensive to carry out in more densely populated communities. In ad­ dition, some Danish gasworks were both technologically and organi­ zationally connected to local water supplies and sewage systems. Hence in the late 19th century gas pipes became organic elements in the process of Danish town building. During the present decade, when the Nordic energy systems are in a “liberation” process, Den lysende gas offers illuminating back­ ground to contemporary events. Ole Hyldtoft has written a wellresearched history ofa Danish peculiarity. The national idiosyncrasy of the book may, however, constitute a barrier at least to part of its potential audience. The Danishness is interwoven into the book so tightly that to comprehend it fully a knowledge of the language is not enough. The reader must be thoroughly acquainted with Danish society in order to realize what has been written between the lines. Timo Myllyntaus Dr. Myllyntaus teaches economic and social history at the University of Helsinki. He is the author of Electrifying Finland: The Transfer of a New Technology into a Late Industrialising Economy (London: Macmillan, 1991). The Early History ofData Networks. By Gerard J. Holzman and Bjorn Pehrson. Los Alamitos, Calif.: IEEE Computer Society Press, 1995. Pp. xi+ 291; illustrations, maps, figures, appendices, notes, bibli­ ography, index. $35.00 (hardcover). The tide of this book is a bit misleading, although one can see the reason for it. From the authors’ perspective on modern telecom­ munications, any system for getting information from one place to another looks like a data network, especially if its designers concern themselves with such things as codes and error messages. Nonethe­ less, it is surprising to find under a cover so titled a richly detailed account of the optical telegraph in France and Sweden, including a translation of a treatise on the subject by the designer of the Swedish system, Abraham N. Edelcrantz, published in Stockholm in 1796. Edelcrantz shares center stage with the creator of the first optical telegraph system, Claude Chappe, whose initial experiments on long-distance communication by sight and sound caught the atten­ tion of the French Convention in 1793 as war was breaking out. TECHNOLOGY AND CULTURE Book Reviews 1005 Chappe had tried several devices and codes before settling on a sem­ aphore system, at first called a tachygraphe but then renamed a télé­ graphe. This consisted of a rotating main beam (regulator) with a rotating wing (indicator) at each end. In a series of modifications of the allowable configurations of the beam and wings, Chappe moved from a code based on the ten digits to ninety-four positions ranging over the digits, the alphabet, and a set of common syllables. When combined with a 94 X 94 table of values, the system allowed for 8930 different words and phrases to be conveyed by a sequence of three settings of the semaphore. Messages went from source to destination through a string of relay stations in visual contact at dis­ tances of 10-15 kilometers. The first line from Paris to Lille in 1794 grew over the next fifty years into a network connecting the major cities of France, northern Italy, and the Netherlands. By 1852, 556 stations traversed some 4,800 kilometers. By then, however, the elec­ trical telegraph had gone into service and quickly rendered the opti­ cal system obsolete. Edelcrantz (his name after elevation to the nobility; he was born Clewberg) learned of Chappe’s semaphore in 1794 and quickly re­ produced it, thereby attracting the attention of the new Swedish king, Gustav IV. Commissioned to study a full telegraph network, Edelcrantz soon replaced the semaphore with a 3 X 3 array of shut­ ters held either open or shut. Treated as three columns of threedigit...