An ordinary photographic negative appears to the unaided eye as a series of smooth density values which may either gradually merge one into the other or meet one another along sharply defined lines. If such a negative be greatly enlarged one can see that the image at each point is not smooth but has structure and that lines which appeared sharp are really diffuse. The series of developed images illustrates, by successive stages of magnification, the transition from the familiar smoothedover negative image to the microscopic granular image comprised of a haphazard distribution of discrete silver grains. It is thus the individual grain that is the seat of the photographic process and the latent image problem is concerned with the photochemical process that occurs in the individual grains of the emulsion during exposure to light and prior to development.