Inside of the bronze ball there's a lead weight that is free-swinging on an axle that's on two bearings that pass in between, across it, like this, that counterbalance this weight.
铜球的内部 有个铅块， 绕着一个轴心作自由摆动， 轴心就在两个轴承 之间移动， 像这个样子，就抵消了这个重量。