The state of photography nowadays is such that the amateur and professional alike are surrounded by an overwhelming mass of all kinds of materials—cameras, plates, films, papers, chemicals—with the inevitable result that any one individual who does not succeed with a certain class of goods will prefer to leave it and try another, rather than try to ascertain the reasons for his failure. It is not enough, furthermore, to be satisfied if we are successful; let us endeavour to find out why success has attended our efforts, every bit as much as failure, so that a clear knowledge of the principles of photography shall guide our future work, and make us as independent as possible of facts, formulæ, and friends.