Experiments were performed using a continuous electromagnetic, or J X B, body force to accelerate the plasma. Argon and helium plasmas were accelerated in a cylindrical channel after a free jet had been established. The specific impulses and efficiencies obtained by expanding helium through an arc-jet-nozzle arrangement is compared to the specific impulses and efficiencies obtained using a continuous electromagnetic field to accelerate the gas. The dependence of the electromagnetic body force upon the accelerating arc current was found, in general, to agree with theoretical predictions.