Two types of methods have been previously used to relate the macroscopic decay of polarization in a dielectric specimen to a microscopic decay function defined in terms of molecular motions. The first is based on Kubo's theory of non-equilibrium statistical mechanics combined with Kirkwood's theory. T h e second is based on the use of Debye's rotational diffusion equation.Glarum has made a calculation of the first type, which predicts an exponential macroscopic decay in the case of a liquid assumed to have particularly simple properties. Scaife and the authors have made a calculation of the second type, whch for the same liquid agree with each other in predicting a non-exponential macroscopic decay, but disagree with Glarm's calculations.In this paper it is shown that, if Glarum's calculation is modified at one point, the results then agree with the calculations of the second type made by Scaife and the authors, The modification consists in the use, at a certain point, of a macroscopic decay function which we feel to be more justified physically than that used by Glarum.

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The absolute calibration, linearity, angular response and wavelength response of three different commercially available UVA meters have been evaluated. The meters exhibited wide variations in accuracy in determining UVA irradiance, combined with significant differences in response at different angles and wavelengths. It is considered that these variations may lead to uncertainties in ultraviolet radiation dosimetry when assessing the relation between the risk of cutaneous carcinoma associated with oral psoralen photochemotherapy and UVA dose.

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