The Krarup Cable: Invention and Early Development

Abstract

The Krarup Cable: Invention and Early Development HELGE KRAGH During the first decade of the 20th century the idea of “loading,” that is, the improvement of transmission quality of telephone cables or wires by increasing their self-inductance, was turned into a highly successful innovation. The history of this development and the prior discussion of its possibilities in scientific circles have often been dealt with by historians of science and technology, who have seen it as an exemplary case study in the transfer of scientific insight into techno­ logical practice.1 However, most historical studies have concentrated on the development in Great Britain and the United States and identified loading with the coil-loading method invented by George Campbell and Michael Pupin. The other tradition in loading technol­ ogy, the uniformly loaded cable, has received little historical attention. The possibility of improving long-distance telephony by continuous loading was mentioned by the British electrican and physicist Oliver Heaviside as early as 1887, but it first reached an innovative stage through the work of C. E. Krarup, a Danish telegraph engineer. Hence, cables of this kind were generally known as “Krarup cables.” Dr. Kragh is senior researcher in history of technology at the TISK project, Roskilde University Centre, and the author of works on the history of modern theoretical physics. His latest book is Dirac: A Scientific Biography (Cambridge, 1990). He has completed a book manuscript on the history of long-distance telephony, and his research now focuses on the development of cosmology after 1945. He gratefully acknowledges financial support from the Danish Research Council of Humanities and the assistance of Mark H. Clark in supplying him with copies of American patents. 'The historical literature of telephone transmission science and technology includes the following works: Thomas Shaw, “The Conquest of Distance by Wire Telephony,” Bell System TechnicalJournal 23 (1944): 337—421; James E. Brittain, “The Introduction of the Loading Coil: George A. Campbell and Michael I. Pupin,” Technology and Culture 11 (1970): 36-57, reprinted in Terry S. Reynolds, ed., The Engineer in America (Chicago, 1991), pp. 261-82; Neil H. Wasserman, From Invention to Innovation: Long-Distance Telephone Transmission at the Turn of the Century (Baltimore, 1985); Bruce J. Hunt, “‘Practice vs. Theory’: The British Electrical Debate, 1888-1891,” Isis 74 (1983): 341-55; Paul J. Nahin, Oliver Heaviside: Sage in Solitude (New York, 1988); D. W. Jordan, “The Adoption of Self-Inductance by Telephony, 1886- 1889,” Annals ofScience 39 (1982): 433—61. Other relevant works will be mentioned below.© 1994 by the Society for the History of Technology. All rights reserved. 0040-165X/94/3501 -0002$01.00 129 130 Helge Kragh The development that led to this technology took place in France, Germany, and Denmark, and submarine telephone cables loaded according to Krarup’s design were mostly used on the Continent. Scientific insight into how to solve a particular technological prob­ lem often results in more than one solution. In this case, the recognition of the beneficial nature of increased self-inductance gave rise to two technologies, discrete and uniform loading. Since these were solutions to basically the same problem, telephony over long distances or underwater, they entered the technological world as competitors. I believe that this picture has a more general validity and thus is better suited to illustrate important features in the technologi­ cal process. A scientifically based recommendation of what to do in order to solve a particular problem is generally implemented in more than one way, and a technical problem is generally addressed in more than one way, thus resulting in a competitive situation. This article deals with the history of the uniformly loaded cable in Northern Europe and pays particular attention to the invention of that technology in 1901-2. Whether continuous or discrete, inductive loading was the result of predictions from electromagnetic theory. I will briefly reexamine the way in which science in this case helped to produce a new technology and argue that the two versions of loaded cables related differently to theoretical physics. The emergence of two alternative solutions to the problems of long-distance telephony precipitated a competition between the Pupin and Krarup technolo­ gies, which lasted for more...