  We present evidence for a coherent shear signal in a field containing the
z=1.2 radio-source PKS1508-05. Since there were no intervening mass
concentrations known before targeting this field, we interpret this signal as
due to weak lensing by large-scale structure. This result is the outcome of a
re-analysis of the observations of Fort et al. (1996) in the fields of three
high redshift QSO/radio-sources. Several tests of the robustness of the signal
were performed: subdivision of the field and tests using simulated data with
randomized ellipticity orientation; using the pixel-to-pixel autocorrelation
function method to measure the shear; using the correlation function of the
galaxy ellipticities with bootstrap resampling to estimate errors and to find
the typical angular separation that dominates the signal. We find that the
field of PKS1508-05 contains a robust shear signal that is coherent over the 2'
by 2' field. The signal is detected at a high level of significance (99.6%)
using the tests described above. The amplitude of the shear on a scale of 1' is
about 3%, which is consistent with theoretical expectations from weak lensing
by large-scale structure.
