=Color Sensitiveness.=—Complete specifications for an aerial plate cannot be made solely on the basis of its speed, contrast, latitude, threshold, and other sensitometric values which have to do only with the intensity of the light acting on it. These in general apply to photography from low altitudes, where the illumination and natural contrast of the subject are the only factors to consider. When higher altitudes are reached the interposition of haze decreases the already deficient contrast, calling either for the development of more contrast in the plate, or for the use of color filters to cut out the action of the blue and violet light predominant in haze. Along the lines discussed in the last section, it is not surprising to find that some plates are better than others for bringing out gradations masked by haze, even though no filters are used and though the plates are similar in color sensitiveness. But the limitations to securing contrast by manipulating the characteristic curve of the plate are soon reached, and it becomes necessary to resort to haze-piercing color filters, used with _color sensitive_ plates. Roughly, two general types of color sensitive emulsions may be distinguished: first, those in which sensitiveness to green and yellow is added to the natural blue sensitiveness, and second, those sensitive in a useful degree to all colors of the spectrum. The former are called _iso-_ or _ortho-chromatic_, the latter _panchromatic_ emulsions. Spectrograms exhibiting the distribution of sensitiveness throughout the spectrum for several representative plates are shown in Fig. 105. Orthochromatic plates are adequate for use with light yellow filters and have the slight practical working advantage that they can be handled by red light. Panchromatic plates are necessary for use with dark orange or red filters. They must be handled in total darkness or in an exceedingly faint blue-green light, taking advantage of the common drop in sensibility in that region of the spectrum. Plates can, indeed, be sensitized for the red alone, leaving a gap of almost complete insensibility in the green, as shown in the fourth spectrogram of Fig. 105. When used with a yellow filter these plates behave as do panchromatic plates with a red filter. [Illustration: FIG. 105.—Spectrograms of representative photographic plates: _a_, ordinary plate; _b_, orthochromatic plate; _c_, specially green-sensitive plate; _d_, red sensitive plate, insensitive to green; _e_, panchromatic plate; _f_, specially red-sensitive panchromatic plate.]