In order to develop a method of heterochromatic photographic photometry which can be used to compare line intensities at different wave lengths in the ultraviolet, the sensitivity, speed, contrast, scale, and fogging characteristics of six standard emulsions were studied in the region 4350-2144A. Light from a constant source (mercury vapor lamp or cadmium spark) was dispersed in a high aperture monochromator and the energy distribution was measured by a thermopile and d’Arsonval galvanometer. The light was diminished in intensity uniformly at all wave lengths by means of a diaphragm and screens. Density-log intensity and density-log time curves were plotted at fourteen wave lengths for each emulsion, in some cases for several times of development, and from these the values of intensity contrast and time contrast were measured. All plates showed a decreasing contrast with decreasing wave length, although some showed a minimum at 2800A, with somewhat increased contrast for a short distance at shorter wave lengths. All showed an increased speed at shorter wave lengths over that in the visible as far down as 2500A, when the speed for all except the Schumann plates decreased rapidly. Cramer contrast process plates, with extremely high contrast in the visible, showed greatly decreased contrast at shorter wave lengths, though even here the contrast was greater than that of the other plates. The reciprocity law was found to hold very closely with this plate at all wave lengths above 2500A (and possibly below), over the time and intensity range studied. Eastman Speedway plates showed fairly uniform speed and contrast down to 2500A. These two plates were found excellent for photometry, the first having high contrast and slow speed, and the second low contrast and high speed. They showed the least tendency to acquire chemical fog of any of the plates. The Schumann plates were found unsuitable for photographic photometry, having large variations in sensitivity over their surfaces. Data are also given for several oil-coated emulsions in the region 2700-2144A. Oil can be used not only to increase speed and contrast at wave lengths below 2500, but to make these factors vary less with wave length.
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