Mass excesses of the nuclides ${\mathrm{H}}^{1}$, ${\mathrm{D}}^{2}$, ${\mathrm{C}}^{12}$, ${\mathrm{C}}^{14}$, ${\mathrm{N}}^{14}$, ${\mathrm{O}}^{18}$, and ${\mathrm{Ar}}^{40}$ were determined by measurement of 18 parent molecule ion doublets with the mass synchrometer. The ${\mathrm{C}}^{14}$-${\mathrm{N}}^{14}$ difference, 156.44\ifmmode\pm\else\textpm\fi{}0.29 kev, was obtained from measurements on the doublets [${\mathrm{C}}^{14}$${\mathrm{O}}^{18}$-${\mathrm{O}}_{2}$], [${\mathrm{N}}^{14}$${\mathrm{O}}^{18}$-${\mathrm{O}}_{2}$], [${\mathrm{C}}^{14}$${\mathrm{H}}_{4}$-${\mathrm{H}}_{2}$O], [${\mathrm{C}}^{14}$C${\mathrm{H}}_{2}$CO], and [${\mathrm{N}}_{2}$${\mathrm{H}}_{4}$-${\mathrm{O}}_{2}$] and other doublets which give some of those above. This is in excellent agreement with the value of 156\ifmmode\pm\else\textpm\fi{}1 kev obtained from determination of the ${\mathrm{C}}^{14}$ beta end point. The consistency of these data supports the 1 kev upper limit for the neutrino rest mass derived from the ${\mathrm{H}}^{3}$-${\mathrm{He}}^{3}$ mass difference and the ${\mathrm{H}}^{3}$ beta end point, and also supports the argument that mass synchrometer data are essentially free of systematic errors of the magnitude required to account for discrepancies between nuclear reaction and mass spectrographic mass excesses of ${\mathrm{C}}^{12}$ and ${\mathrm{O}}^{18}$. Mass excesses of the light nuclides determined were slightly higher than recently published mass synchrometer data, but agreement was generally within 1 \ensuremath{\mu}MU.