The Fine Structure ofHα

The fine structure of $\mathrm{H}\alpha$ was investigated using Fabry and Perot interference patterns produced in the light of ordinary and heavy hydrogen. The auxiliary spectroscopic dispersion was sufficient to separate the patterns of ${\mathrm{H}}^1\alpha$ and ${\mathrm{H}}^2\alpha$. Accurate photometric methods were used in interpreting the spectrograms and a new method of analyzing the observed patterns was developed. Following are the principal results: (1) Three components of each line are directly observable, while the two remaining components predicted by theory could not be resolved. (2) The observational evidence indicates definitely the same relative intensities of the components for ${\mathrm{H}}^1\alpha$ and ${\mathrm{H}}^2\alpha$. (3) The relative intensities insofar as they are determined depart markedly from the theoretical values. These departures are consistent with the hypothesis of a diminished population of atoms in the $3D$ energy states. (4) The fine structure constant was determined yielding $\frac{1}{\alpha }=137.4\mathrm{}\pm 0.2$. There is some evidence of systematic dependence of this result on conditions of excitation in the source so that the probable error overestimates the accuracy of the result. The correct value probably lies between 137 and 138.