The hyperfine separation of tritium has been measured with respect to the hyperfine separation of hydrogen by comparing the frequency of the tritium maser with that of a hydrogen maser. The result is $\Delta \nu \left(\mathrm{T}\right)=1\mathrm{}516701470.8087\pm 0.0071$ Hz, where it is assumed that $\Delta \nu \left(\mathrm{H}\right)=1\mathrm{}420405751.8$ Hz. Wall shifts were measured for tritium and hydrogen for FEP Teflon at 35°C. For a spherical bulb, $d$ cm in diameter, the fractional wall shift for hydrogen is $-(3.61\mathrm{}\pm 0.54)\times \frac{{10}^{-10\mathrm{}}}{d}$, and for tritium it is $-(3.14\mathrm{}\pm 0.47)\times \frac{{10}^{-10\mathrm{}}}{d}$.

• Received 9 January 1967

DOI:https://doi.org/10.1103/PhysRev.158.14