Méthode pratique pour déterminer exactement le temps de pose en photographie : applicable à tous les procédés et à tous les objectifs, indispensable pour l'usage des nouveaux procédés rapides gélatino-bromure et autres
A French photography manual by R. Clément, published in Paris by Gauthier-Villars in 1880, written for photographers working with the new fast gelatino-bromide plates and other processes. Its first picture is a shield-shaped publisher or device emblem with a banner reading Laborare et Nolli, a motto-style mark rather than a technical figure. The second is a plain geometric diagram of two triangles meeting at a point O, with lettered lines B, C, b, c and f, showing how angles and ratios of an optical setup were worked out.
