Let us, for the sake of simplicity, call the mass determined in the first way the inertial mass and that determined in the second way the gravitationalmass.
为简便起见，我们把用第一种方法所测定的质量叫做惯性质量，而把用第二种方法所测定的质量叫做引力质量。
2
Since this identity of inertial and gravitationalmass was fundamental for the formulation of the theory of relativity, we are justified in examining it a little more closely here.
因为惯性质量和引力质量的相等是阐明相对论的基本原理，我们应当在这里把它更细致地考查一番。
3
The astronomers found an "X-ray mass" only a tenth of the mass found using the gravitational lens method.