Using the Stratton and Houghton theory, Foitzik34a showed that the transition stage between dependence and independence of wavelength occurs for particle sizes between 0.5 and 2 μ. Clouds and fogs should thus show no selective transmission, and this in general is borne out by observation.
Harrison47 discussed the mechanism of light scatter in the atmosphere and summarized the theory as given in the literature. He used this to determine the visual range under various conditions of scatter and extended it to calculate the "photographic range" for a variety of combinations of emulsions and filters covering the spectral range from the blue to the infrared. His results agree surprisingly well with some of the published data, for example, those of Hugon,55 Hulburt,57 and Mohler.80 In general, he found that no increase in range would be expected when infrared emulsions were used if the visual range were less than one third of a mile, and at a visual range of 20 miles the increase would only be about 20 per cent.
The reader who is interested in a fuller discussion of this subject should read the papers referred to in the bibliography, particularly the book by Middleton,77 and the articles by Harrison47 and Breckenridge.16
See end of Chapter XV.