Deviations from Lambert’s cosine law for the light emitted by W, Mo, and Ta. The deviations for all three metals is very much of the same order. The brightness in each instance increases from the normal value at normal emergence gradually with increase in emergence angle to about 75° by about 20 per cent. From there on the brightness decreases rapidly to zero at grazing emergence. Straight filaments of circular cross-section have average brightnesses viewed normal to their axes which are about 3 per cent greater than the normal brightnesses (W 2.8 per cent, Mo 3.6 per cent, Ta 2.7 per cent). The average brightness of a filament, considering all directions, is about 5 per cent greater than the normal brightness (W 4.4 per cent, Mo 6.2 per cent, Ta 4.3 per cent).
Polarization of light emitted by W, Mo, and Ta. The light emitted by these materials starting with zero polarization for normal emergence increases with the angle of emergence, at first slowly, to about 95 per cent at grazing emergence. The polarizations of the light from straight filaments of circular cross-section viewed normal to their axes amount to about 20 per cent (W 19.3 per cent, Mo 20.8 per cent, Ta 18.5 per cent).
Change in optical constants of tungsten with temperature. Values obtained have depended on the variations of the emissivity and the reflectivity for the two polarized components. At room temperature 3.86 and.81 were obtained for n and k, at 1900°K 3.85 and.89 were obtained. This difference checks well with observed values of emissivity for normal emergence.
© 1926 Optical Society of AmericaFull Article | PDF Article
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