At means of determining the temperature of a hot solid body by photographic means has been developed. For the purposes of this experiment, a General Electric tungsten ribbon filament lamp, with an operating range of 12 to 18 amperes was used as the object. From published curves, it was found that the color temperature of the filament varied from 2220K to 2990K over the above amperage range. It is therefore possible to vary the color temperature with a powerstat and to monitor it with an ammeter. Using two front surfaced mirrors, the lamp illuminated both sides of a photometric edge so that they both received equal initial illumination. Two different spectral transmission filters were placed in the system, one in the path of each beam, so that each side of the photometer edge was now illuminated by different wavelengths of radiation. One filter was a Kodak 89B wratten filter, which transmits radiation above 730 nm up to 900 nm, but blocks radiation below 730 nm. The second filter was a Kodak #301 infrared cutoff filter which transmits in the visible range from 400 to 730 nm but blocks infrared radiation above 730 nm. At a given lamp temperature, the edge was imaged onto Kodak 2481 High Speed Infrared film which was then processed according to a standardized method. The densities of each side of the image, each exposed by different wavelengths as explained above, are measured, and the corresponding log exposures and exposures are determined from a previously prepared characteristic curve of the film. From this data, a ratio R = E301/E89B was determined. Since this value varied with changing illumination (hence, color temperature), the above procedure was repeated for several color temperatures within the above-mentioned range. The result was a calibration curve of R as a function of color temperature. It was now possible to determine the value of an unknown temperature of the lamp. The above procedure was repeated with the lamp at an unknown setting. By extrapolating the R value for the unknown temperature on the calibration curve, it was possible to determine the color temperature of the lamp. The average percentage of error in this process was found to be below 1.0%
