一些关于氢的东西：，氢气，就像其他元素一样，有同位素，人们在1766年就发现了这一点，卡文迪许分离出原子氢，并且阐述了它的一些性质。
A couple of other things about hydrogen: hydrogen also, like other elements, has isotopes and we already saw that in 1766, Cavendish isolated atomic hydrogen and enunciated some of its properties.
测量结果惊人的准确，他测出了万有引力恒量的参数，在此基础上卡文迪许计算地球的密度和质量。
The result was a remarkably accurate estimate of a parameter called the gravitational constant, and from that Cavendish was able to calculate the density and mass of the earth.
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