Photographic Photometry

A thermoelectric photometer is described, and the theory of photometric measure- ment is developed. The influence of variable fog on the photographic p]~ate, including the Eberhard effect, is investigated. It is shown that, in general, the ratio of the galvanometer deflection for the star to that for the fog in the immediate neighborhood is a measure of stellar magnitude. Experimental evidence is adduced. Since the stand- ards of magnitude (the PoLar Sequence) are located at the pole, the effects on photom- etry of the unavoidable errors of adjustment of the polar axis of the instrument, especially serious in long exposures, are pointed out and steps which should be taken for their reduction are suggested. The difficulties always met in the photometric measurement of plates taken with wide-angle lenses-in particular, distance errors- are discussed. The background effect, due to unresolved clusters and to dark and bright nebulae, is shown to be inappreciable. Experiments were made to determine the best method of development. It was found, unexpectedly, that development without rocking or agitation of any kind gave superior results. A catalogue of the magnitudes and approximate positions of all stars as bright as i 2.0 photovisual magnitude in the BD zones 88° and 89° is given, with a chart for identification. Comparison is made with Seares's values for normal distribution and mean color indices