  We repurpose tools from the theory of quantitative rectifiability to study
the qualitative rectifiability of measures in $\Bbb{R}^n$, $n\geq 2$. To each
locally finite Borel measure $\mu$, we associate a function $\widetilde
J_2(\mu, x)$ which uses a weighted sum to record how closely the mass of $\mu$
is concentrated on a line in the triples of dyadic cubes containing $x$. We
show that $\widetilde J_2(\mu, x) < \infty$ $\mu$-a.e. is a necessary condition
for $\mu$ to give full mass to a countable family of rectifiable curves. This
confirms a conjecture of Peter Jones from 2000. A novelty of this result is
that no assumption is made on the upper Hausdorff density of the measure. Thus
we are able to analyze generic 1-rectifiable measures that are mutually
singular with the 1-dimensional Hausdorff measure.
