The current is automatically reversed at {TAIL ~ the point} of zero motion of {HEAD ~ the reciprocating mechanism} during each rebound 
The current is automatically reversed at { TAIL ~ the point } of zero motion of { HEAD ~ the reciprocating mechanism } during each rebound
OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH