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The paper describes an instrument for the rapid spectrophotometry of liquids by the spectrographic method. A single exposure, usually of less than 20 seconds, results in a set of spectra which embodies all that is necessary for plotting an absorption curve.

(1) An objective method of treating absorption data is devised for obtaining the most reliable value for the upper limit of continuous β-ray spectra. (2) The effect of geometrical conditions, of change of source-intensity, and of source-thickness on the absorption curve and on the apparent upper limit is discussed. (3) Feather's empirical equation connecting range and energy of β rays is corrected in accordance with more recent determinations. The corrected equation is R=0.536E - 0.165. (4) The method is applied to absorption curves obtained for the β rays emitted from Mg27, Si31 and As76. The values 0.885 ± 0.068 g./cm2., 0.571 ± 0.047 g./cm2. and 1.400 ± 0.024 g./cm2. are in good agreement with the values obtained by other methods.

The absorption coefficient of evaporated zinc sulphide has been measured between 0.27 and 0.60 μm. A kink has been found at 0.332 μm. The effects of cooling at liquid-air temperature and of ageing at 200 °C on the absorption curve have been measured. A comparison has been made with other published results. The Urbach rule for the long-wavelength tail of the absorption curve was found to be followed only by the average curve.

The absorption spectrum of ammonia between 0 6 and 0.9 cm.-1 has been measured at pressures up to 60 cm Hg. From the previous analysis of the fine structure, and the measurement of the widths of the lines at a pressure of 0.5 mm. Hg, the shape of the absorption curve at high pressures has been computed assuming that the widths vary accurately as the first power of the pressure. At a pressure of 10 cm Hg, the computed and observed curves agree within the experimental error; at 60 cm. Hg, the observed attenuation at the lower frequencies is somewhat greater than that computed. Possible reasons for this phenomenon are discussed.