A balanced magnetic probe technique has been used to determine the drive force acting on the plasma sheath during the first pinch. The sheath motion was studied with the probe technique, and with image converter framing pictures. The sheath mass was determined from the velocity and the time integral of the drive force. The results indicate an average pickup coefficient of 0.82 ± 0.06 for the first half of the pinch. Electron density and temperature were determined during the first half of the pinch by measurement of the H&bgr;line profile. Combination of the spectroscopic and mass data indicates an average sheath ionization lower than predicted by theory, but the experimental error in the ionization determination precludes a definite conclusion to this effect.