Theresa Levitt's study of optical work in nineteenth-century France engages a set of themes that has long been at or near the top of the agendas of historians of science: the knotty relationship between science and politics. At the centre of her study are the social and scientific relations between the distinguished French physicists François Arago and Jean-Baptiste Biot. She follows their work in chronological and thematic order, starting from an analysis of their technical and physical work on optics in the first two chapters, and moving from there ‘further into French culture’ (p. 8) in the following chapters, in which she covers astronomy, life sciences, photography and finally the colonial sugar trade and slavery.

On the basis of this material, Levitt asks about the interrelations between scientists’ work and their political engagement, which she takes to be neither ‘disparate activities’ nor ‘parallel structures’ (p. 6). She avoids asking whether Biot and Arago's thoughts on political matters ‘depended’ on their optics, or whether structural changes in scientific or political institutions influenced their scientific investigations and vice versa. Instead, she invites us to look at the ‘cultural act of attaching meaning to the world’ (p. 8), exploring how science and politics converged in Biot's and Arago's lives and how the two negotiated emerging tensions intellectually and institutionally. She traces and analyses the key themes that run through the ‘body of their lives’ work’ (p. 10): light, visibility, forces (seen and unseen), representation of and in the world, and the question of human freedom.

Levitt uncovers fascinating historical, philosophical and political dynamics in this material. She explores theoretical work on colour; questions of (technical and artistic) education in Revolutionary France; intellectual and institutional quarrels over post-Newtonian optics; standardization and communication in scientific and political spaces; and alliances of state, science and industry (as, for example, in colouring and dyeing). My two favourite examples in her rich study are both concerned with the intersection of scientific practice and practices of political participation in the public sphere. In her analysis of Arago's ‘public astronomy’ (p. 89), Levitt explains Arago's ambition to integrate the French public into astronomical observations, to boost science education, and thus to teach the kind of critical reasoning that would do away with ignorance and superstition – phenomena that he suspected to be obstacles for constitutional forms of government (p. 91). Arago also introduced a new instrument and observational technique for photometry into astronomical research, which was meant to yield reliable data for a ‘rationally communicating astronomical community’ (p. 101). Levitt captures a similar dynamic in her analysis of Arago's and Biot's divergent ideas about photographic images and civic participation (p. 149). The production of representation, its legitimacy and reliability, and its effective dissemination and democratization, constitute an exemplary intersection of themes for her ongoing inquiry about optical politics: seeing, forces and transparency. Who, Levitt asks, was a legitimate representer of the world, and who should, if at all, enable larger groups of people to participate in processes of representation, both scientific and political? The convergence of scientific and political rhetoric and action was a pressing question in the period of revolutions in the first half of the nineteenth century in France. The idea of a sphere of rationally communicating individuals implied a space of competing figures, institutions and interests. They provide Levitt with a variety of sites to explore her questions about science and politics and the specifically modern dimensions that this relationship took on in physics in post-Revolutionary France.

Levitt frames her study with two further historical and philosophical questions, which place it in a larger context of concerns in the history of science about the origins and traits of modern physics. With regard to a larger chronology of the history of science in Europe, Levitt's work engages the ‘shadow’ of the Enlightenment, as her title tells, discussing how optical work in the first decades of the nineteenth century is usually regarded as one of the seminal moments during which a modern physics – characterized by precise experimental inquiry and quantitative mathematical analysis – was created out of the ‘ferment’, to use Rousseau and Porter's term, of eighteenth-century natural philosophy. Her work helps us understand core aspects of Enlightenment science and the ways we usually understand its relation to the ‘modern kind’ of science that emerged in the professionalization, mathematization and institutionalization of the nineteenth century. She distinguishes important nuances in this historical process – continuities and discontinuities – during which science and society ‘became’ modern.

At a philosophical level, furthermore, Levitt links her study's questions about optics, light and visibility to the metaphor of the mirror and the loss of its innocence in the nineteenth century. The mirror, ‘realism's most enduring icon’ (p. 1), as she says, polarizes light when it reflects it. Polarization was an optical phenomenon that Arago and Biot placed at the centre of their work, and it also raised questions about the reliability of visual representation of the world and the correspondence of our knowledge to an outside world. The mirror's loss of innocence challenged this virtue and called into question the very ‘modernity’ of physics, philosophy and representation that was being established at the time. In this regard, Levitt's discussion nicely anticipates crises of modernity that are usually connected with modernist movements in the later nineteenth and early twentieth centuries. Her arguments about science, politics and the modern condition come full circle as she carves out a historical space for Arago's and Biot's lives and works that envelopes beginnings and crises of the modern pursuit of the physical sciences.