A third form of the apparatus includes {HEAD ~ a pair} of {TAIL ~ conductors} not in mutual contact, but each in contact with a third conductive member when in its rest position 
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A third form of the apparatus includes { HEAD ~ a pair } of { TAIL ~ conductors } not in mutual contact , but each in contact with a third conductive member when in its rest position
OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH