This is a study of the life and work of a Calvinist experimental philosopher based at Nîmes in the second quarter of the seventeenth century. Hitherto Claude Guiraud has been no more than a footnote in the history of the New Science whose very existence is only known through two brief biographical notices published in the eighteenth century. Building on Guiraud's small extant correspondence, the spasmodic references to his activities in the letters of others, and his two optical treatises, which survive in manuscript in a Leipzig library, Mazauric has painstakingly reconstructed the life of a forgotten savant. Guiraud, it is revealed, was a well-to-do bachelor who never left the town of his birth and was free to devote his life to his intellectual interests. More importantly, he was part of a network of mathematicians, experimentalists, and atomists, mostly Protestants, who flourished in the Midi in the 1630s and 1640s. The coterie was mainly, if not entirely, inspired by Sébastien Basson, a professor at the Protestant college of Die in the early seventeenth century, who published an atomist textbook in 1621. Its members included Gassendi, at Aix, and Fermat, at Toulouse, and there were a large enough number at Montpellier and Castres to form a scientific academy for a short time. Guiraud in particular had close contact with the French capital, thanks to his childhood friendship with Samuel Sorbière, who had left Nîmes for Paris in 1638. Through Sorbière, Guiraud and his scientific work became known to Mersenne and his circle, and thanks to Mersenne, also to Descartes, though he is only cited as an anonymous author in their letters.

Guiraud's primary interest was optics. The two surviving manuscripts consist of a treatise on light, probably written in 1639, and a commentary on Hobbes's critique of the optics of Thomas White, which was composed in the mid-1640s. Guiraud had apparently acquired a fragment of Hobbes's text from his Montpellier associate Pierre Saporta. In the first work, Guiraud sets out a corpuscular and vacuist view of light, which shows a good knowledge of existing atomist theories and takes issue with Descartes's plenist and instantaneous theory. In the second, Guiraud is particularly keen to demonstrate the insufficiency of Descartes's explanation for the angle of incidence being equal to the angle of reflection. For Guiraud this has to be a physical—not a mathematical—explanation, and the cause is to be found in the spherical nature of light particles. The law would not hold if the particles were shaped differently. Mazauric compares and contrasts Guiraud's optical works with the other optical treatises that were published in France in the 1630s and 1640s. Not only does she show that he was fully abreast of the current literature but also that he had a critical and original mind. It is presumably for this reason that the second half of the volume contains an edition of the two works, along with Guiraud's correspondence, prepared by Sylvain Matton. The text, with useful interpretative notes, is published in both the Latin original and a fluent French translation.

In writing the intellectual biography of Guiraud, Mazauric has performed a sterling service. It is now evident that the world of French experimental philosophy in the second quarter of the seventeenth century was much richer than so far suspected, and cannot be simply measured by the reach of the Mersenne correspondence. It is also clear that the Catholic Gassendi was not unique: his atomist views were shared and shaped by a number of his Protestant contemporaries in the Midi. In her conclusion, Mazauric suggests that this is more than chance. The Calvinist view of an all-powerful God, she argues, cast doubt on Aristotelian hylomorphism and encouraged the belief that nature was inert and could only be understood mechanically. This is too trite, as she herself acknowledges, but she has certainly succeeded in placing the Huguenots center stage in the development of French and European atomism. She has also effectively shown that in the age of Mersenne, French experimental philosophy was not Paris-centric, as often assumed. It had a beating, independent heart in the south. This is a clearly written and informative book that anyone interested in the early history of experimental philosophy will profit from reading. It is a model of historical detective work.