A Manual Of Photography

OO HISTOBY OF PHOTOGBAPHY. discoveries that honour their native land,” on the argument that the invention did not admit of being secured by patent, for as soon as published all might avail themselves of its advantages,” that it should have been guarded by a patent right in England, which has, however, nearly run its course. From the primary importance of this very beautiful branch of tue photographic art, I shall devote some space to a description of the original process, reserving for the division devoted to the manipulatory details the description of each improvement which lias been published, having any practical advantage, either by lessening the labour required, or reducing the expense. Ehe pictures of the daguerreotype are executed upon thin sheets of silver plated on copper. Although the copper serves principally to support the silver foil, the combination of the two metals appears to tend to the perfection of the effect. It is essential that the silver should be very pure. The thickness of the copper should be sufficient to maintain perfect flatness, and a smooth surface ; so that the images may not be distorted by any warping or unevenness. Unnecessary thickness is to be avoided on account of the weight. The process is divided by Daguerre into five operations. The first, consists in cleaning and polishing the plate, to fit it for receiving the sensitive coating.on which light forms the picture. The second is the formation of the sensitive loduret of silver over the face of the tablet. The third is the adjusting of the plate in the camera obscura, for the purpose of receiving the impression. The fourth is the bringing out of the photographic picture, which is invisible when the plate is taken from the camera. The fifth and last operation is to remove the sensitive coating, and thus prevent that susceptibility of change under luminous influence, which would otherwise exist, and quickly destroy the picture. First Operation.—A small phial of olive oil—some finely carded cotton—a muslin bag of finely levigated pumice—a phial of nitric acid, diluted in the proportion of one part of acid to sixteen parts of water, are required for this operation. The operator must also provide himself with a small spirit-lamp, and an iron wire frame, upon which the plate is to be placed whilst being heated over the lamp. The following figures represent this frame. The first view is as seen from above. The second is a section and elevation, showing the manner in which it is fixed. The plate being first powdered over with pumice, by shaking the bag, a piece of cotton dipped into the olive oil is then carefully rubbed over it with a continuous circular motion, con-