Index of Refraction of Pure Water for Sodium Light from 15° to 100° C.—Very few observations had previously been made for temperatures above 50° C. A precision spectrometer was used. The brass prism with optical glass windows was gold plated inside to prevent contamination of the pure gas-free water tested, and means were provided for keeping the temperature within 0.1° C. Many readings were taken and the average values are probably accurate to within about 0.00002. When reduced to vacuum they are well represented by the empirical formula: $n=1.33401-{10}^{-7\mathrm{}}(66t+26.2\mathrm{}{t}^2-0.1817\mathrm{}{t}^3+0.000755\mathrm{}{t}^4)$. The temperature coefficient dn/dt changes from - 8${\mathrm{}\left(10\right)\mathrm{}}^{-5\mathrm{}}$ at 15° to - 30${\mathrm{}\left(10\right)\mathrm{}}^{-5\mathrm{}}$ at 100°.

Index of Refraction of Commercially Pure Ethyl Alcohol and Carbon Bisulphide for Sodium Light from 15° up to the Boiling Points.—While Kahlbaum's ethyl alcohol, 99.8 per cent. absolute, and Baker's C.P. C${\mathrm{S}}_2$ were used, the absolute values obtained differ somewhat from those given by others for pure samples. Nevertheless the temperature coefficients are probably not affected by the slight amount of impurity present and are of interest because very few results are available for liquids at temperatures above 40° C. The results correspond to the empirical equations: $\frac{\mathrm{dn}}{\mathrm{dt}}(\mathrm{ethyl}\mathrm{alcohol},15\mathrm{} \mathrm{to} {70}^{\circ })=-{10}^{-6\mathrm{}}\mathrm{}[404+0.44(t-15)+0.0075\mathrm{}{\mathrm{}(t-15\mathrm{})\mathrm{}}^2];\frac{\mathrm{dn}}{\mathrm{dt}}(\mathrm{C}{\mathrm{S}}_2,15\mathrm{} \mathrm{to} {45}^{\circ })=-{10}^{-6\mathrm{}}\mathrm{}[766+5.12(t-15)-0.105\mathrm{}{\mathrm{}(t-15\mathrm{})\mathrm{}}^2]$.

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