Longitudinal stresses and critical radial electric fields were observed in electrospinning jets. Viscoelastic stresses in the straight segment of electrically-driven jets of polymer solutions were determined from the propagation of a lateral displacement pulse along the jet. The displacement was applied to the orifice from which the jet issued. A sensitive video camera was used to observe the location and intensity of the light emitted from corona discharges that were created at particular locations around the jet. Since the onset of a corona discharge in air occurred predictably at a critical value of the radial electric field, the corona showed where, along the tapering jet, the electric field reached the critical value. The corona continued, for a short distance along the jet, while the electric field at the surface decreased, and then stopped. When corona was present, many segments of the collected fibers were split longitudinally into two or more smaller, side-by-side nanofibers.