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A new process of graphic reproduction and photography has been developed. The basic process, known as xerography, is dry, direct positive-to-positive, rapid, and has a number of potential applications in graphic arts and related fields. As a photographic process, xerography employs a re-usable plate consisting of a thin layer of a photo-conductive material on an electrically conductive base. The plate is sensitized by electrostatic charging immediately before use. After exposure, the image is developed by dusting the plate with a micronized powder. Prints are made by transferring and fixing the powder image to paper or other materials. The plate can be used many times to produce additional images. Xerography also provides a unique and simplified process of graphic reproduction, particularly in printing and duplicating.

This experiment requires simple equipment and readily available materials and should serve as a pleasant introduction to the field of solid state chemistry.

Imaging devices, other than pure optics in the case of incoherence, often work in a nonlinear way, consequently linear transfer theory fails to apply. Nonlinearities may be of the zero-spread or the finite-spread type. Conditions are examined to determine if describing functions for certain classes of objects may be used as generalized transfer functions, retaining some of their favourable properties. Adjacency effects can be linear or nonlinear. Electro-optics, radiology, photography, xerography, and the visual system are briefly treated in view of these concepts.

Image recording processes which yield non-absorbing, light-scattering images exhibit characteristics not encountered in conventional photographic processes. Some of these characteristics must be considered in any evaluation of the quality of light-scattering images. One such characteristic is the dependence of the projected image of a light-scattering transparency upon the relative aperture of the projector lens. This effect is examined in the case of a conventional projection system. The detail-recording characteristics of the Frost thermoplastic xerography process have been examined. A tentative model for this process is proposed, and the usefulness of this model is discussed on the basis of experimental data on the recording of sinusoidal test patterns. An unusual characteristic of the process has been observed and has been elucidated further by measurement of noise spectra.

An expansion of the electrostatic field into a Fourier integral of spatial harmonics provides the natura starting point for a definition of a describing function taking the place of the modulation transfer function of simpler systems. The definition becomes meaningful after it has been shown how the field is connected with plate thickness, toner dimensions, initial voltage, distance of development electrode, and the optical density of the developed image. An explanation of the adjacency effect of xerography is given. Conclusions can be drawn as to the best working conditions of xerography for line copy and pictorial reproductions. Sensitivity as function of plate thickness and voltage will be discussed. The results are in qualitative agreement with experience. Quantitative tests have still to be made.

Field calculations provide a better understanding of xerography. The basic equations are given and some typical results are presented and analyzed. Particular emphasis is placed on adjacency effects and the effect of a development electrode.