Whenever the force of gravity lessens, the second end of {HEAD ~ the beam or wire breaks contact} with the tube, creating {TAIL ~ an open switch} 
Whenever the force of gravity lessens , the second end of { HEAD ~ the beam or wire breaks contact } with the tube , creating { TAIL ~ an open switch }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL