After the failures of 1858 and 1865, the Atlantic was finally spanned by a submarine cable in 1866. A boom in cable laying ensued as British firms built a global cable network would remain a bulwark of British imperial and commercial power well into the twentieth century. The surging cable industry created a demand for electrical knowledge that stimulated the emergence of physics teaching laboratories in Britain. These laboratories turned out scientists, engineers, and teachers trained in precision electrical measurement—essentially cable testing room techniques. The cable enterprise also set the direction of British electrical research in the late nineteenth century, including the reception and articulation of Maxwell’s field theory. In the early 1880s a circle of young “Maxwellians” emerged in Britain, among them Oliver Heaviside, a former cable engineer who had taken up Maxwell’s theory as a tool to address signalling problems. Guided by ideas about energy flow and signal propagation, in 1884 Heaviside recast the long list of equations Maxwell had given in his Treatise into the compact set now universally known as “Maxwell’s equations.” The form of Maxwell’s field theory that passed into textbooks in the 1890s was rooted in important ways in the global cable network.

"When the first underground and submarine telegraph cables were laid around 1850, engineers noticed that sharp signals sent in at one end emerged at the other badly blurred and appreciably delayed. This “retardation” grew worse on longer cables and threatened to make operation of the proposed 2000-mile Atlantic line unprofitably slow. Retardation presented British physicists and engineers with both an intriguing physical phenomenon and a serious practical problem, and they studied it closely from the 1850s on.

Latimer Clark, a prominent British cable engineer, brought retardation to Michael Faraday’s attention late in 1853, and Faraday’s published account of the phenomenon served to publicize both retardation and the ideas about the electromagnetic field that he invoked to explain it. Faraday’s paper led William Thomson (later Lord Kelvin) to reprint two papers on field theory he had written in the 1840s, and later in 1854 a related cable question prompted Thomson to work out what became the accepted mathematical theory of signal transmission. Moreover, it was at just this time, and largely under Thomson’s guidance, that James Clerk Maxwell first took up the study of electricity, with results that were to transform electromagnetic theory."

James Clerk Maxwell’s field theory of electromagnetism had important and previously unrecognized roots in the cable industry of the mid-nineteenth century. When he took up electrical physics in 1854, the subject was permeated by a concern with cable problems. Guided by William Thomson, Maxwell soon adopted Faraday’s field approach, which in 1861 he sought to embody in a mechanical model of the electromagnetic ether. Seeking evidence to bolster the electromagnetic theory of light to which this model had led him, Maxwell joined the British Association Committee on Electrical Standards, which had been formed in 1861 largely to meet the needs of the submarine telegraph industry. Maxwell’s work on the committee between 1862 and 1864 brought home to him the value of framing his theory in terms of quantities he could measure in the laboratory—particularly the “ratio of units”—rather than relying on a hypothetical mechanism. Maxwell’s shift from his mechanical ether model of 1861 to his seemingly abstract “Dynamical Theory of the Electromagnetic Field” of 1864 thus reflected the often overlooked role concerns rooted in cable telegraphy played in the evolution of his thinking.

An agreed system of electrical units and standards was crucial to building a workable cable systemin the 1860s, as well as to advancing electrical science. Without such standards, it was almost impossible to extend accurate electrical knowledge beyond a single laboratory or testing room. Amid conflicts over competing standards and in response to rising demands from the telegraph industry, in 1861 William Thomson called on the British Association for the Advancement of Science to establish a Committee on Electrical Standards. The committee proved very influential, and its work marks one of the most important points of intersection between electrical science and technology in the mid-nineteenth century. Led by James Clerk Maxwell ,and Fleeming Jenkin, the committee determined the value of the ohm experimentally in 1862–64 and distributed standard resistance coils around the world. Standard ohms soon became a key part of quality control in the cable industry; indeed, the aim in manufacture became to make a cable that was, in effect, a chain of standard ohms strung end to end, its properties at each point known and recorded.

After the failure of the first Atlantic cable, proponents of oceanic submarine telegraphy sought to parry claims that the task they had attempted was simply impossible and to argue that it instead resulted from a series of correctable errors. Their first step was to pin as much blame as they could on Wildman Whitehouse while separating his practices from those of proper electrical scientists and engineers. The Atlantic Telegraph Company then teamed with the British government to establish a Joint Committee to investigate how such disasters might be avoided in the future. In 1861 the committee issued a massive Report that identified the rationalization of methods and standardization of materials as keys to bringing order and reliability to an industry that had hitherto lacked both. The Joint Committee Report exemplified the power of expertise backed by official authority, and it soon became the bible of British cable practice as the idiosyncratic methods of Whitehouse and other cable amateurs gave way to William Thomson and Latimer Clark’s emphasis on precise and standardized measurement. Guided by this new measurement-based approach to telegraph engineering, the Atlantic cable project was resurrected and would finally succeed in 1866.

"The first attempt to lay a transoceanic cable, the Atlantic cable project of 1856–58, had far-reaching effects on electrical theory and practice. Although it was launched by an American, Cyrus Field, the project soon came to be dominated by British capital and technical expertise. Among the leading figures in the Atlantic Telegraph Company were Charles Bright, the young chief engineer; Wildman Whitehouse, a Brighton surgeon turned electrical experimenter; and William Thomson, professor of natural philosophy at Glasgow and a member of the company’s board of directors. Whitehouse and Thomson had argued about signal propagation and cable design before joining the company; the circumstances of this dispute, and of its temporary resolution early in 1857, shed valuable light on how scientific and practical concerns interacted in the project, particularly around questions of measurement. The dispute flared again when the Atlantic cable failed in September 1858 after only a month of fitful service. The response to that failure would shape British cable telegraphy and electrical physics for decades to come."

In January 1889, in the wake of Heinrich Hertz’s dramatic discovery of electromagnetic waves, the British physicist Oliver Lodge declared that with this experimental confirmation of James Clerk Maxwell’s electromagnetic theory of light, “the whole domain of Optics is annexed to Electricity, which has thus become an imperial science.” Lodge had hit on a very up-to-date way to express the preeminence electrical science had achieved by the last decades of the nineteenth century. But in 1889 electricity was an imperial science in a less metaphorical sense as well: it lay at the scientific heart of submarine telegraphy, one of the characteristic technologies of the Victorian British Empire.

In 1902, a consortium of British imperial powers laid a string of cables across the Pacific, connecting Canada to Fiji, Australia, and New Zealand. The new cables completed the “All Red Line,” circling the globe while touching only on British-controlled territories, and set the capstone to the worldwide British cable network (Figure 7.1). That network would remain of vital strategic and economic importance for decades to come, but as the twentieth century dawned, both physics and electrical technology found themselves moving in new directions. Cable telegraphy had nourished the rise of field theory, but that theory had led in its turn to the discovery of electromagnetic waves and then to the development and promotion by Oliver Lodge, Guglielmo Marconi and others of practical systems of wireless telegraphy.

Treating Earth as a system in which life plays an important role in controlling the environment is not new. In fact, speculation on how the physical and living elements of the Earth interact goes back to antiquity, and earlier, with deities capriciously intervening in the affairs of the human population. The notion of a single integrated system mediated by gods was the stuff of religion and legend. The Greek cosmologists dismissed arbitrary gods as controllers of the universe. Instead, they considered that the order of nature and the cosmos follows eternal cycles. Democritus (c. 460–370 BCE) proposed an atomist theory of matter that invoked an early form of the conservation of energy: atoms are in eternal motion. The Roman poet and philosopher Lucretius (96–55 BCE) drew on the atomic theory of Democritus to account for a variety of terrestrial phenomena, such as earthquakes and lightning, according to physical principles. Some Greek philosophers, including Thales (624–546 BCE), Anaximenes (585–528 BCE) and Heraclitus (535–475 BCE), taught a philosophical doctrine that there is a form of life in all matter. The rationalist philosophical styles of the ancient world were lost until the world of ideas was revived in Europe in the fifteenth century by the rise of humanism in Italy.

The previous chapter described the genesis of a new interdisciplinary field, oceanography, which led to enormous advances in broadening our understanding of the history of the ocean basins. Seafloor spreading at the ocean central ridges and the ancient seafloor descending into the trenches at the ocean margins were the key conceptual breakthroughs for discovering the interior dynamics of the Earth system. But turning that imaginative concept of a dynamic Earth into a realistic package of evidence, as required by the scientific method, continued to be elusive in the 1950s and early 1960s. As is often the case in the history of Earth science, though, the convincing evidence eventually came from two unexpected but related lines of investigation: studies of rock magnetism and magnetic surveys of the seafloor. Investigation and follow-up of the phenomena in these fields turned out to be of critical importance for reconstructing the history of the motions of portions of the terrestrial surface. This is a tale of serendipity, in which research on the magnetic record fossilized in rocks finally led to the seal of approval for a brilliant concept: plate tectonics. I’ll begin with the puzzle of how and where the geomagnetic field is generated. The properties of the geomagnetic field are observable from surface measurements of its direction, strength and variations.