Spectroscopic Verification of Redshifts Predicted by Gravitational Lensing

We present spectroscopic observations of 21 faint arcs seen in the HST image of the cluster Abell 2218 for which redshifts have been predicted using a lensing inversion technique based on the cluster mass model discussed by Kneib et al. (1996) 1. This mass model is constrained by multiply-imaged sources seen in the HST image, 2 of which have known redshifts. Preliminary results indicate that the spectroscopic redshifts obtained agree well with predicted values and this gives us conndence that the lens inversion redshifts of even fainter arclets are similarly well constrained. These arclets are well beyond reach of current spectrographs. We conclude that the technique remains a highly promising method of studying the statistical properties of the faint eld population.