Determination ofemfrom theHα−DαInterval

Photographs were taken with a 3 mm étalon of the interference pattern of $\mathrm{H}\alpha$ and $\mathrm{D}\alpha$ from a discharge in the two gases mixed in equal proportions. The interval between the intensity peaks due to the low frequency major components of the two isotopes was measured with the microphotometer used as a comparator. Corrections were made to the observed positions of the intensity peaks to change them to the positions of the centers of the components. These corrections were based on the intensities, positions, and half-intensity breadths of the components as experimentally determined, and upon certain assumptions relative to the shape of the components. An interval between components of 4.14700±0.0004 ${\mathrm{cm}}^{-1\mathrm{}}$, when reduced to vacuum, was obtained. By combining this with recently determined values of the atomic weights of hydrogen and deuterium as reported by Livingston and Bethe, the wave number of $\mathrm{H}\alpha$ as determined by Houston, and the physical Faraday as computed by Birge, a value of 1.7579±0.0004×${10}^7$ e.m.u./gram is obtained for the value of $\frac{e}{m}$.