A photoelectric spectrophotometer of high accuracy

Details are given concerning the components used in constructing a photoelectric spectrophotometer employing as light-sensitive element a vacuum emission photocell of a modern type with central plate cathode. It is claimed that the instrument as a whole has a linear response over the necessary range of photocurrents and the method by which this property was tested is described. The instrument has been applied to the measurement of spectral transmissions of the International Standard Blue Filter R 3.28 and the results, which are in good agreement with the internationally adopted figures, are given in full. The effect of temperature on this filter is shown also.