In the second half of the nineteenth century, British firms and engineers built, laid, and ran a vast global network of submarine telegraph cables. For the first time, cities around the world were put into almost instantaneous contact, with profound effects on commerce, international affairs, and the dissemination of news. Science, too, was strongly affected, as cable telegraphy exposed electrical researchers to important new phenomena while also providing a new and vastly larger market for their expertise. By examining the deep ties that linked the cable industry to work in electrical physics in the nineteenth century - culminating in James Clerk Maxwell’s formulation of his theory of the electromagnetic field - Bruce J. Hunt sheds new light both on the history of the Victorian British Empire and on the relationship between science and technology.