There he leant over the wall and lowered the lamp, only to behold the vortex formed at the curl of the returning current.
然后他在岸墙上俯身探望,把灯放低,但只能看到回流的浪卷形成的漩涡。
英语百科
Ground (electricity)
For different type of earthing system refer Earthing system.
In electrical engineering, ground or earth is the reference point in an electrical circuit from which voltages are measured, a common return path for electric current, or a direct physical connection to the Earth.