  The in-plane resistivity and uniform magnetic susceptibility anisotropies of
$BaFe_{2}As_{2}$ are obtained with a new method, in which a large
symmetry-breaking uniaxial strain is applied using a substrate with a very
anisotropic thermal expansion. The resistivity anisotropy and its corresponding
elastoresistivity exhibit very similar diverging behavior as those obtained
from piezo-stack experiments. This suggests that the resistivity anisotropy is
more a direct measure of magnetism than of nematicity, since the nematic
transition is no longer well-defined under a large strain. In strong contrast
to the large resistivity anisotropy above $T_{N}$, the anisotropy of the
in-plane magnetic susceptibility develops largely below $T_{N}$. Using an
itinerant model, we show that the observed anisotropy ($\chi_{b}>\chi_{a}$) is
determined by spin-orbit coupling and the orientation of the magnetic moments
in the antiferromagnetic phase, and that the anisotropy is dominated by
intra-orbital ($yz,yz$) contributions of the Umklapp susceptibility.
