The internal intensity ratio of Hα and of Dα

A Geissler-Wood discharge tube was designed for use as the light source of Hα or Dα line. The tube was cooled in liquid air under low pressure to reveal the fine structure of the spectral lines. Four different separations, 7.6, 7.8, 8.0, and 8.2 mm, were used in the Fabry-Perot interferometer. Ten spectroscopic plates were measured for Hα and ten others for Dα. The internal intensity ratio of Hα and of Dα was found to be 0.808±0.004 and 0.803±0.003, respectively, as compared to the theoretical value of 0.806. This study indicates that the experimental value of the intensity ratio between the two main component groups agrees with the theoretical value when pure hydrogen or pure deuterium gas is used in the discharge tube and the discharge is at its maximum intensity.