Coefficient of viscosity of helium by the constant deflection method.—Using carefully purified He, which showed only a spectroscopic trace of H, six series of measurements at about 23° C gave ${\eta }_{23}=1962.3\mathrm{} {\mathrm{}\left(10\right)\mathrm{}}^{-7\mathrm{}}$. This is about 2 per cent less than values obtained by the capillary method, but is believed correct to within 0.1 per cent.

Coefficients of slip of helium and oxygen for polished and unpolished silver oxide surfaces.—The values obtained for ${\zeta }_{76}·{\mathrm{}\left(10\right)\mathrm{}}^7$ are: for the unpolished surface, 123 (He), 61.1 (O); for the polished surface, 160 (He), 64.5 (O). These are probably accurate to one per cent. From Maxwell's equation, the values for complete diffuse reflection, which are the minimum values, are computed to be 191 (He) and 70 (O). The low experimental values suggest a "reverse-specular" reflection or perhaps the abnormal momentum transfer at the surface may be attributed to an excess of molecules leaving the cylinders due to the release of oxygen at low pressures. The change of the slip with time, observed in previous work, is shown to be due to the release of occluded gases, chiefly oxygen in the case of a silver oxide surface.

Increase in the stiffness of the steel suspension wire, noted by Van Dyke, continues.

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