This seventh edition is the first to offer a long chapter devoted to the process on gelatin-silver bromide which has just been developed and which is the major revolution in photography at the end of the 19th century.
"It is certain that, from now on, photography is really within the reach of all and that its applications will become much more numerous. Indeed, it is enough to obtain dry plates with gelatin-silver bromide and to study during a small number of days the manipulations of the development of the image, to obtain results which were, until now, the exclusive domain of a few specialists ". (p. 373).