The History of the Fedorov Stage
The History of the Fedorov Stage
Among the various methods of optical study of crystals, the universal Fedorov method occupies a well-deserved place. Its purpose is to identify minerals based on their optical properties. These are the properties that are expressed in the size, shape and position of the optical indicatrix in the crystal. The concept of the orientation of the indicatrix in the crystal space was used before the advent of the Fedorov method (for example, A. Michel Lévy, A. Lacroix).
In 1891, E. S. Fedorov proposed determining the relative position in space of some crystalline and optical directions inside a crystal. In order to solve this problem, it was necessary to have a device so that the section would rotate not only in its plane on the microscope stage, but also in space. In addition, it was necessary to be able to measure these rotations and determine the positions of the directions being sought. It was proposed to use the following two devices.
Stage type I:
Stage type II:
The tilt of the preparation on the stage leads to deviation of the directions of the rays in the crystal. Therefore, following the construction of the first models of the stage, E. S. Fedorov proposed glass hemispheres (segments), between which the preparation is sealed with glycerin.
The original model of the universal, or theodolite, stage had two axes corresponding to the two axes of the theodolite. Quite quickly the stage was replaced by the next, more complex model of the stage with four axes. The original model of this stage looked like this:
A later model of the four-axis stage had two supports.
Later, many works appeared that developed individual aspects of the Fedorov method. New, additional devices appeared, such as Nikitin and Berek's rotating compensators, special objectives, condensers. In 1929, a new step was made in improving the design of the universal stage by Emmons, who added another (fifth) axis of rotation.
Until the 1960s, three-axis, four-axis and five-axis schemes continued to develop, largely associated with changes in mechanical units. Subsequently, the theodolite method was practically replaced by X-ray structural and conventional goniometric analysis.