The German label on this white plaster model indicates that it is a model of a wave surface for a positive uniaxial optical crystal, L. Brill Ser. 10.1 No. 7. Such a model always has an outer shell that is a sphere and an inner shell that is an ellipsoid. However, this model is an ellipsoid with one octant cut away to reveal part of a sphere. Thus this is a model of a wave surface of a negative uniaxial crystal whose Brill model is No. 158, Ser. 6, No. 3. The correct label for this model appears on 1982.0795.21.
This is one of a series of models designed at the Munich polytechnic high school under the direction of Alexander Brill in 1880.
Compare to 1985.0112.124.
L. Brill, Catalog, 1892, p. 13, 87.
For examples of related models, with a reference to a related publication, see the Goettingen collection of mathematical models, model numbers 283 (Schilling #356) and 284 (Schilling #357).
Francis A. Jenkins and Harvey E. White, Fundamentals of Optics, New York: McGraw Hill, 1976, p. 553-555.
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