Intellectual history tempts us to think of the history of space/time as a series of moments that mark irreversible epistemic shifts—the invention of the magnetic compass, the “discoveries” of new continents, the ability to measure longitude. With Zero Degrees: Geographies of the Prime Meridian, his wonderful new book on the long and uneven history of the Prime Meridian, Charles Withers teaches us that changes in how we understand our spatial and temporal world can be heterogeneous, uncertain, sometimes faltering, and always poised between alternative understandings of global identity. For geographers, “the world,” as Withers notes, “depended on where you started from” (64), and, despite its claim not to be producing a history of modernity, Withers's expert and thoughtful marshalling of a multitude of official reports, commentaries, maps, and charts ably demonstrates how modernity is always a series of different starts and different geographical positions.

Withers tells the story of the Prime Meridian from early attempts to regulate global space (including many competing national meridians) to the International Meridian Conference of 1884, in Washington, DC, that eventually decided on the Greenwich Meridian, and on to that decision's “afterlife” in which the instabilities and idiosyncrasies of global measurement persisted—it was not until the early twentieth century that Paris gave up its own claim. Despite the lure of scientific precision and the neutral ring of the phrase “degree zero,” the final triumph of Greenwich came about more through the gradual rejection of other possibilities than through its intrinsic merit, and after a long stretch of time in which there were many different local meridians amid many different ideas of geographical form.

The book is deeply and impeccably researched, and immensely detailed, but it is always a fascinating and compelling read as Withers takes us into the complex negotiations and competing ideas that eventually led to the 1884 Washington conference. Withers has always paid close attention to how knowledge is formed in and between specific places, events, institutions, and movements of material texts. In this new book, his ability to move between micro-historical observations and world-historical ideas furnishes the story of the Prime Meridian with a great number of practical concerns amid its intellectual history. The attempt to measure the globe was not just political or mathematical; it faced such matters as the visibility of sighting stations, the way operatives got on with each other, even the conditions of the weather. National differences in units of measurement had to be accounted for, and local differences resolved within nations (local and customary measurements were not abolished in Britain until 1835). Thus, as Withers demonstrates, the pursuit of “accuracy” was at once scientific, political, and contingent. Like much of Withers's previous work, Zero Degrees shows how books matter—how meridians were used in teaching texts, or how “nautical almanacs” worked to establish the correspondence between navigational practice and astronomical prediction.

Zero Degrees shows how the idea of a Prime Meridian is pulled on one direction by material contingencies and political circumstance and in the other by astronomical observation. Debates had to balance practical consideration of daily life, the obligation to address the needs of navies and merchant ships with those of astronomers, and national prestige. Sometimes decisions were taken in the immediate aftermath of wars, rather than with reference to scientific abstractions. The long build-up to the Washington conference was fraught by competing claims because the “needs of practical navigation were not those of geography” (98).

The way in which we imagine the globe involves gradual shifts in spatial understanding. The Prime Meridian moves from the Ptolemaic limit or edge (of the known world) to a proposed beginning from which other lines will radiate. The world begins not only where you start from, but also where you stand. A “cartographic” meridian on a map, and the less common “observed” meridian (based on an astronomical calendar and essential for the development of navigation in the eighteenth century) are different classes of knowledge. Thus, the seeming neutrality of “zero degrees” posed many questions: Was the globe one or many? What is “neutrality” in the first place? To the French it meant a form of abstraction, to the British and Americans it had more to do with common measurements established by commercial practices and nautical routes.

Withers's brilliant analysis of the Washington conference shows not only why but also how resolutions were achieved—usually by a process of systematic rejection of ideas rather than a comparative overview of them. Particularly, Withers shows us how small a part abstract scientific measurements played in the proceedings. Sandford Fleming, the Scottish-Canadian member of the British delegation to the Washington Conference (and one of many key players Withers scrupulously documents), hoped for a cosmopolitan solution that favored no nation but would instead “tend towards the general benefit of all mankind” (167). Fleming's humanist gesture was rooted in his desire for the universal standardization of time. Here again Withers shows how the promotion of an abstract ideal can be rooted in practical considerations: Fleming was also a railway engineer.

Despite its long historical sweep and proliferation of detailed examples, the book is very clearly structured. It moves from classical geography to the later ramifications of the 1884 conference, teasing out the implications of assertions and decisions that went into the gradual internationalization of science and the acceptance and uses of universal time. The book will be of great interest not only to geographers but also to historians and literary scholars like myself (not least because en passant Withers properly thinks through and contextualizes those two phenomena so beloved by cultural historians of the nineteenth and early twentieth centuries: the establishing of railway time and the anarchist Martial Bourdin's plot to blow up the Greenwich Observatory). With a generous quota of detailed illustrations, it is hard to imagine a better, fuller or more coherent account of how modern time came to be.