Luminance thresholds for the Bezold-Brücke hue shift

This study presents data on the luminance difference at which a hue difference is first perceived between two identical spectral lights. Thresholds were obtained for both luminance increments and decrements from a 2.00 log troland standard for wavelengths between 470 nm and 690 nm. A predicted luminance threshold for each wavelength was calculated based on wavelength discrimination data and the Purdy constant hue contours; i.e. that luminance at which the constant hue contour intersects the wavelength discrimination bound for a given wavelength. A generally good agreement was obtained between observed and predicted values.     

A device for facilitating the computation of the first four moments about the mean

A mechanical device is described which materially reduces the time, labor, and probability of errors which are involved in the computation of certain moments about the mean. The use of the device is illustrated with the computation of the mean, standard deviation,g ₁ as a measure of skewness, andg ₂ as a measure of kurtosis of data from a given study.Grateful acknowledgment is made to the Holter Research Foundation of Helena, Montana for the grant-in-aid which made possible the development of this device.