Normal spectral radiation was measured in the range of 1 to 10 μ from layers of 0.3-μ alumina powder of various thicknesses and compactions resting on a platinum substrate. The substrate was heated and the layer lost heat from its upper surface by radiation and free convection. The measurements are compared to the predictions obtained from the two-flux theory applied on a spectral basis, in combination with the equation of conduction. Qualitative correspondence is indicated but the magnitudes of the predicted and measured radiation differ by as much as 40 percent. The inference is that the specification of optical properties is not quite correct and that the thermal conductivity of the powder layer is substantially less than expected.

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