improvements that have made photography what it is; to do honour to those who have toiled and given, or sold, the fruits of their labour for the advancement of the art; to set at rest, as far as dates can succeed in doing so, any questionable point or order of precedence of merit in invention, application, or modification of a process, and to enable the photographic student to make himself acquainted with the epochs of the art, is the extent of my ambition in compiling these records. With the hope of rendering this work readily referable and most comprehensive, I shall divide it into four periods. The first will deal broadly and briefly with such facts as can be ascertained that in any way bear on the accidental discovery, early researches, and ultimate success of the pioneers of photography. The second will embrace a fuller description of their successes and results. The third will be devoted to a consideration of patents and impediments; and the fourth to the rise and development of photographic literature and art. A strict chronological arrangement of each period will be maintained, and it is hoped that the advantages to be derived from travelling some of the same ground over again in the various divisions of the subject will fully compensate the reader, and be accepted as sufficient excuse for any unavoidable repetition that may appear in the work. With these few remarks I shall at once enter upon the task of placing before the reader in chronological order the origin, rise, progress, and development of the science and art of photography. FIRST PERIOD. THE DARK AGES. More than three hundred years have elapsed since the influence and actinism of light on chloride of silver was observed by the alchemists of the sixteenth century. This discovery was unquestionably the first thing that suggested to the minds of succeeding chemists and men of science the possibility of obtaining pictures of solid bodies on a plane surface previously coated with a silver salt by means of the sun's rays; but the alchemists were too much absorbed in their vain endeavours to convert the base metals into royal ones to seize the hint, and they lost the opportunity of turning the silver compounds with which they were acquainted into the mine of wealth it eventually became in the nineteenth century. Curiously enough, a mechanical invention of the same period was afterwards employed, with a very trifling modification, for the production of the earliest sun-pictures. This was the camera-obscura invented by Roger Bacon in 1297, and improved by a physician in Padua, Giovanni Baptista Porta, about 1500, and afterwards remodelled by Sir Isaac Newton.