  A first measurement of the 1-jettiness event shape observable $\tau_1^b$ in
neutral-current deep inelastic scattering is presented. For the measurement,
the equivalence of $\tau_1^b$ to the DIS thrust observable defined in the Breit
frame is utilised. The data were taken by the H1 experiment at HERA from 2003
to 2007 at a centre of mass energy of $\sqrt{s}=319 \text{ GeV}$. The data
amount to an integrated luminosity of $351.6\text{ pb}^{-1}$. The
triple-differential cross sections are presented as a function of the
1-jettiness $\tau^1_b$, the virtuality of the exchanged boson $Q^2$ and the
inelasticity of the event $y$. The data exhibit a sensitivity to the strong
coupling constant and to resummation and hadronisation effects, as well as to
the parton distribution functions of the proton. The data are compared to
selected predictions.
