A Weak Gravitational Lensing Analysis of Abell 2390

We report on the detection of dark matter in the cluster Abell 2390 using the weak gravitational distortion of background galaxies. We find that the cluster light and total mass distributions are quite similar over an angular scale of ~7' (1 h^-1^ Mpc). The cluster galaxy and mass distributions are centered on the cluster cD galaxy and exhibit elliptical isocontours in the central ~2' (280 h^-1^ kpc). The major axis of the ellipticity is aligned with the direction defined by the cluster cD and a "straight arc" located 38" to the northwest. We determined the radial mass-to-light profile for this cluster and found a constant value of (320 +/- 90) h M_sun_/L_sun v_, which is consistent with other published determinations. We also compared our weak lensing, azimuthally averaged radial mass profile with a spherical mass model determined by a virial analysis of the cluster. We find good agreement between the two profiles, although there are weak indications that the mass model determined from the virial analysis may be falling off more steeply for θ >= 3' (420 h^-1^ kpc).