. Electron microscopy; proceedings of the Stockholm Conference, September, 1956 . Fig. I. Ray diagram illustrating the principle of the dark- field system. At the right is shown the special annular aper- ture. are collected with a thermal precipitator directly on beryllium films about 30 A thick. After collection they are heated to 550 C to remove organic matter and condensed oil vapour. At the same time the beryllium oxidizes to form a crystalline oxide film, the diffraction pattern of which is used to calibrate the diffraction pattern of the mine dust. Using a three-stage electron microscope
. Electron microscopy; proceedings of the Stockholm Conference, September, 1956 . Fig. I. Ray diagram illustrating the principle of the dark- field system. At the right is shown the special annular aper- ture. are collected with a thermal precipitator directly on beryllium films about 30 A thick. After collection they are heated to 550 C to remove organic matter and condensed oil vapour. At the same time the beryllium oxidizes to form a crystalline oxide film, the diffraction pattern of which is used to calibrate the diffraction pattern of the mine dust. Using a three-stage electron microscope, bright- field micrographs and the diffraction patterns of several parts of the specimen are recorded. The constituents are identified by comparison of the diffraction patterns with standard diffraction pat- terns of substances, the presence of which is sus- pected, or by comparison with the index. Having determined the various chemical constitu- ents present in a sample by electron diffraction, it may be desirable to establish in which parts of the specimen the various constituents are present. For example, assume that several constituents have been identified in a sample containing a large number of particle sizes and shapes. It might be that one or other constituent is confined to particles of a partic- ular size range or of a particular shape. If this is so, and the relation between each constituent and the particle size range or shape can be established, then it is a simple matter to determine the number and the sizes of the particles of each chemical compound present. To establish the relationship, if any exists, between a particular constituent and any peculiarities of the sample, a new system of dark-field electron micro-
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