The Effect of the Angular Aperture of a Telephotometer on the Telephotometry of Collimated and Non-Collimated Beams*

It is shown theoretically that in telephotometry in a foggy atmosphere, large errors may arise from the scattering of light by the fog into the telephotometer. These errors depend both on the angular aperture of the telephotometer and on the half-angle of the cone of air illuminated by the distant lamp. Some experimental results are given, which show even larger errors than the hypothetical atmospheres chosen for theoretical investigation.