## Essai d'optique sur la gradation de la lumiere.

Paris: Claude Jombert, 1729.

First edition. Bouguer states for the first time in this work ‘Lambert’s law’, that the intensity of a collimated beam of light decreases exponentially with distance (Lambert stated it thirty years later in his *Photometria*). He also describes his method of comparing the relative brightness of two objects.

A very nice copy in contemporary binding of the founding work of photometry. “Bouguer is regarded as the founder of photometry, the branch of optics concerned with measuring the intensity of light. His two most important contributions to the subject are contained in his

*Essai*, the first part of which states his method of comparing the relative brightness of two lights by using the eye as a null indicator (i.e., to establish the equality of brightness of two adjacent surfaces) and applying the laws of inverse squares. The second part contains the first statement of what is often called Bouguer's law: that in a medium of uniform transparency, the light remaining in a collimated beam is an exponential function of the length of its path in the medium. This law was restated thirty-one years later in Lambert's

*Photometria*and is thus sometimes referred to as Lambert's law” (DSB). Norman 283.

8vo: 166 x 100 mm. (22), 164, (4:errata) pp. and 3 engraved folding plates. Contemporary mottled calf, richly gilt spine, all edges and boarders gilt, head of spine with some chipping, hinges slightly worn, engraved book plate to front paste down. A fine copy.

Item #2212

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Price:
$4,250.00
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