摘要
Ⅰ. INTRODUCTION Early in 1917, Einstein proved that there is a wave solution of gravitational field in vacuum as an approximate solution of weak gravitational field, if these fields satisfy some conditions. This solution corresponds to a plane gravitational wave. When the wave propagates along x-axis, the polarized wave will be determined by 2-rank symmetric tensors in yz-plane. So this is a transversal wave. The approximate conditions of weak field
