BOUGUER (Pierre). Essai d'optique, sur la gradation de la lumière. Paris: Claude Jombert, 1729. - In-12, 169x100: (12 ff. first blank), 164 pp, (2 ff.), 3 plates. Granulated basane, cold fillet framing the boards, ornate ribbed spine, red speckled edges (period binding). First edition, dedicated to the Count of Maurepas, of this sought-after work by mathematician, physicist, geodesist and hydrographer Pierre Bouguer (1698-1729). It is divided into five sections: Méthodes de mesurer la force de la lumière. - Transparency & opacity. - Method of calculating the forces of light passing through different thicknesses of transparent bodies, when the rays are substantially parallel. - Method of calculating the forces of light, when the luminous body is not at an infinite distance. - De la diminution que souffre les lumières en traversant les corps qui ne sont pas partout de même densité. According to Jean-Édouard Morère: "One must [...] consider the Essai d'Optique sur la gradation de la lumière (1729), as an important work which modifies optics by the principles it formulates, the experimental techniques it uses, by the expression and resolution of fundamental problems for astronomy, knowledge of the earth, the arts, by what it adds to dioptric and catoptric, by the extension of the applications of analysis and geometry" (Morère, La photométrie: les sources de l'Essai d'Optique sur la gradation de la lumière de Pierre Bouguer, in: Revue d'histoire des sciences, 1965, p..338). The edition is illustrated with 3 folding plates. A good copy in contemporary binding. The margins of pages 28, 29, 71 and 72 are filled with handwritten notes from the period. Some spotting, including a large one on the first cover. Cut to one corner.