  We show here that quadruple lenses can be useful laboratories to probe
whether the potential of the lensing galaxy is purely elliptical or whether an
additional distortion is present in the deflector plane. For this test we only
have to know the relative image positions of the quadruple lens system and the
(relative) center of light position of the lensing galaxy. Furthermore we
introduce new methods which easily allow us to determine the location (rotation
angle relative to the image positions) of the major axis of the lensing galaxy.
In due course we can determine the parity of the four images as well. We apply
these methods to the 8 currently known quadruple lenses and find that in the
case of MG 0414+0534, CLASS 1608+656 and HST 12531-2914 it is impossible to
accommodate the relative image positions and the galaxy position with any
elliptical potential whereas the other five cases can be described very well
with a simple elliptical potential. This method will have important impacts for
$\chi^2$-fits and the reconstruction of galaxy models for quadruple lenses.
