A Spectroscopic Determination ofem

Abstract

A determination of $\frac{e}{m}$ was made by accurately measuring the difference in wave number between the $\mathrm{H}\alpha$ lines of ordinary and heavy hydrogen. The observations were made with a Fabry and Perot etalon used in conjunction with a spectrograph of sufficient resolving power to separate the interference patterns of the two $\mathrm{H}\alpha$ lines. The effects of the weak fine structure components were eliminated and values of $\frac{e}{m}$ were derived from the two main components. The final mean gives $\frac{e}{m}=1.7579\mathrm{}\pm 0.0003\times {10}^7$. From this determination the ratio of the mass of the hydrogen atom to the mass of the electron is found to be 1835.6±${0.2}_5$. There is no indication of systematic errors in the work so that the probable errors may be fairly taken as representing the actual uncertainties in the results.