"Electromagnetism is bipolar, i.e. it attracts and repels. We can shield X-rays, gamma rays, radio waves, etc., but what about gravity? Gravity appears to have only one polarity - - attraction! We have balloons, planes, and rockets that overcome gravity but can we shield against gravity? "
Electrogravitics Systems: Reports on a New Propulsion Methodology. Edited y Thomas Valone, M. A., P.E. Foreword by Elizabeth Rauscher, Ph.D. P.4 (1993)