The coincidence method for the wave-length measurement of absorption bands

Abstract

It was shown by Bryan and Baker (5) that the coincidence method is one of the most accurate of visual methods of measurement. Their observations applied to sharply defined lines of various types. I have found that nearly the same degree of accuracy is obtained when the lines set into coincidence are not sharp, but have blurred edges, like those of absorption or interference bands. The reason for blurred lines being set into coincidence with nearly the same accuracy as sharp ones is to be described in detail elsewhere, with the various physiological factors on which accuracy depends. The method of coincidences has been applied both to direct visual measurements of absorption bands and also in a few cases to photographic records of such bands. In this paper the method of direct visual observation will be considered alone, because more experience has been gained in this connection. It is possible that in future the application to photography will prove the more important because the method would seem to be applicable to such cases as stellar and mass spectra photography.