_Introduction of the Camera Obscura, and other Improvements in Photography._--The "Camera Obscura," or darkened chamber, by means of which a luminous image of an object may be formed, was invented by Baptista Porta, of Padua; but the preparations employed by Wedgwood were not sufficiently sensitive to be easily affected by the subdued light of that instrument. In the year 1814, however, twelve years subsequent to the publication of Wedgwood's paper, M. Niépce, of Chalons, having directed his attention to the subject, succeeded in perfecting a process in which the Camera could be employed, although the sensibility was still so low that an exposure of some hours was required to produce the effect. In the process of M. Niépce, which was termed "Heliography," or "sun-drawing," the use of the Silver Salts was discarded, and a resinous substance, known as "Bitumen of Judæa," substituted. This resin was smeared on the surface of a metal plate, and exposed to the luminous image. The light in acting upon it so changed its properties, that it became _insoluble_ in certain essential oils. Hence, on subsequent treatment with the oleaginous solvent, the shadows dissolved away, and the _lights_ were represented by the unaltered resin remaining on the plate. _The Discoveries of M. Daguerre._--MM. Niépce and Daguerre appear at one time to have been associated as partners, for the purpose of mutually prosecuting their researches; but it was not until after the death of the former, viz. in 1839, that the process named the Daguerreotype was given to the world. Daguerre was dissatisfied with the slowness of action of the Bitumen sensitive surface, and directed his attention mainly to the use of the Salts of Silver, which are thus again brought before our notice. Even the earlier specimens of the Daguerreotype, although far inferior to those subsequently produced, possessed a beauty which had not been attained by any Photographs prior to that time. The sensitive plates of Daguerre were prepared by exposing a silvered tablet to the action of the vapour of _Iodine_, so as to form a layer of Iodide of Silver upon the surface. By a short exposure in the Camera an effect was produced, not visible to the eye, but appearing when the plate was subjected to the vapour of Mercury. This feature, viz. the production of a _latent_ image upon Iodide of Silver, with its subsequent development by a chemical reagent, is one of the first importance. Its discovery at once reduced the time of taking a picture from hours to minutes, and promoted the utility of the Art. Daguerre also succeeded in fixing his proofs, by removal of the unaltered Iodide of Silver from the shadows. The processes employed however were imperfect, and the matter was not set at rest until the publication of a paper by Sir John Herschel, on the property possessed by "Hyposulphites" of dissolving the Salts of Silver insoluble in water.