A line of high-intensity light formed around a translucent ( or transparent ) particle mounted, for example, in a refractive-index liquid on a glass microscope slide, and illuminated from below. The line of light is caused by concentration by split reflection or refraction.
The bright halo near the boundary of a transparent particle that moves with respect to that boundardy as the microscope is focused through the best focus.
a band or rim of light visible along a grain/crystal boundary in plane-polarized light
A band or halo of light (due to diffraction/refraction) seen at the periphery of a specimen when the refractive indices of the specimen and its mounting medium are different; it is used to determine refractive index. In practice, the Becke Line is produced by reducing the numerical aperture of the substage condenser, and focusing above and below the plane of best focus; the Becke Line always moves toward the material of higher refractive index on focusing above the plane of best focus. (Named after the Austrian geologist, mineralogist, and petrologist, Friedrich Johann Karl Becke, 1855-1931, who devised the method).
When the liquid phase of a microscopical mount has arefractive index different from that of the solid phase, a line or narrow band of light can be observed around or just within the outlines of the specimen as the microscope tube is raised or lowered from its position of best focus. The presence of the line indicates the difference in index referred to, and its absence, there-fore, indicates similarity of index between the specimen and its mounting fluid. The Becke line is useful in determining the refractive index of transparent, microscopic particles. See refractive index (n) by Becke line.