A description is given of a device which automatically sweeps the meridian once each five minutes and records the intensity of the auroral green line (5577 A) in each 10° step. It is almost completely insensitive to white light, but produces a warning signal if the white light becomes very bright. The response is roughly logarithmic over a range of 10 000 to 1 in intensity. The intensities are recorded directly and also in digital form. For the latter, five steps of intensity are distinguished and punched in paper tape; each step corresponds to a factor of 10 and the scale agrees fairly closely with the accepted International Brightness Coefficients.
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