Using an apparatus previously described in which ions formed by impact of electrons of energy ($V_1+V_2$), or by secondary processes, are pulled from the ionization chamber by the field $V_3$ and then analyzed magnetically by Dempster's method, the relative numbers of ions of type ${\mathrm{N}}_1^{+}$ and ${\mathrm{N}}_2^{+}$ are measured for various pressures and voltages. At low pressures (less than ${10}^{-5\mathrm{}}$ mm) only ${\mathrm{N}}_2^{+}$ was observed; as the pressure was increased the percentage of ${\mathrm{N}}_1^{+}$ increased regularly and reached 60 at.006 mm. The percentage of ${\mathrm{N}}_1^{+}$ was markedly greater when helium at a relatively high partial pressure was present. Below 24 volts, no ${\mathrm{N}}_1^{+}$ ions were produced, although ${\mathrm{N}}_2^{+}$ ions appeared with ($V_1+V_2$) greater than 17 volts. These ${\mathrm{N}}_2^{+}$ ions must therefore be stable toward collisions, while above 24 volts ${\mathrm{N}}_2^{+}$ ions are produced which may be disrupted on collision to form ${\mathrm{N}}_1^{+}$ ions. The critical potentials for nitrogen of 16.95 and 24.6, then, correspond to the formation of ${\mathrm{N}}_2^{+}$ (stable) and ${\mathrm{N}}_2^{+}$ (unstable). ${\mathrm{N}}_1^{+}$ ions are therefore produced only by dissociation of unstable ${\mathrm{N}}_2^{+}$ ions. The percentage of ${\mathrm{N}}_1^{+}$ was found to be independent of the field $V_3$ from 2.7 to 27 volts, hence the dissociation of an unstable ${\mathrm{N}}_2^{+}$ ion is independent of its speed over this range. ${\mathrm{N}}_1^{++}$ ions are not produced at all below 500 volts. The ${\mathrm{N}}_2^{-}$ ions found by Smyth were present but too weak to be studied. A diagrammatic representation of the electrons distributed in the two types of ${\mathrm{N}}_2^{+}$ ion is suggested in accordance with the ideas of G. N. Lewis. Correlation with spectroscopic evidence indicates that the negative bands are emitted by the stable ions.

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