Some ground movements, such as lunar tides, still must be fought with more active devices, such as computer-controlled electromagnets that push and pull on tiny magnets glued to the mirrors.

• 一些地表位移，比方说潮汐所引起的，还得用更积极的装置去对付，例如用电脑控制的电磁铁，来推拉黏在镜子上的小磁铁。