Improvements in apparatus and techniques of measurement of the $2{}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}-2\mathrm{}{}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}$ level shifts in hydrogen and deuterium are described. The more accurate results are ${\mathcal{S}}_{\mathrm{H}}=1057.77\mathrm{}\pm 0.10$ Mc/sec and ${\mathcal{S}}_{\mathrm{D}}=1059.00\mathrm{}\pm 0.10$ Mc/sec. These values are compared with results of quantum electrodynamic calculations.

The shape of the resonance curves has been examined in great detail and compared with theory. Assuming the theoretical value of the radiative width and hyperfine splittings, excellent agreement is obtained. Further, if only the radiative width is assumed, measurements on hydrogen reported here confirm theoretical hyperfine splittings to within 0.28 Mc/sec. Since contributions of the hyperfine structure of the $2S$ level have been measured to far greater accuracy, these results constitute a confirmation of the $2P$ hyperfine splittings to an accuracy of 1.0 percent.

• Received 15 September 1952

DOI:https://doi.org/10.1103/PhysRev.89.98