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1949 C-R-TuBE APPLICATIONS 83
current-operated lamps and then the film printed on a high-speed printer also operated on alternating current. Occasionally, the dips in the exposing-light output and printing-light output become synchronous, with resulting light fluctuation in the final projected image. In recent years, many new types of filament construction have been adopted to minimize this defect and to produce as little ripple as possible. The best way to study this ripple is on a cathode-ray oscillograph equipped with a direct-current amplifier so that the ripple may be expressed as a percentage of the total light output. Fig. 16 (a) and (b) illustrates some typical examples of the ripple per
Fig. 17 — Spectrograms of a low-pressure mercury arc at various times in seconds after starting.
centage of a certain lamp. In making these oscillograms, it was also of interest to determine which of these lamps lent themselves most readily to modulation for. the transmission of information over light beams. The incandescence and nigrescence* curves can easily be seen and studied on these cathode-ray oscillograms.
COLOR SPECIFICATION
Another problem in photography and optics is the proper description and specification of various colors. A cathode-ray-tube spectrograph for accomplishing this very result has been described by
1 "Nigrescence" is denned as the process of becoming dark and refers here to the exact manner in which the light output of a lamp decreases after the current is suddenly cut off.