Extension of the Standard Visibility Function to Intervals of One Millimicron by Third-Difference Osculatory Interpolation*

The two empiric representations (Tyndall-Gibson and Walsh) of the visibility of radiant energy yield curves which fail to pass exactly through the values at every 10 mμ adopted as standard; hence, they can not serve as means of obtaining interpolated values. By the method of osculatory interpolation the visibility function is represented as a series of parabolas of the third degree which join at the specified values so as to have a common first derivative at the junction point. The discontinuities in derivatives of higher order which exist at the junction points are sufficiently small to be of no consequence.