said {HEAD ~ inside end} of {TAIL ~ each} of said pole pieces being a concave, curved, inside cylindrical surface which is shaped and sized to conformingly mate with said outside surface of said ferrous cylindrical wall, 
of
said { HEAD ~ inside end } of { TAIL ~ each } of said pole pieces being a concave , curved , inside cylindrical surface which is shaped and sized to conformingly mate with said outside surface of said ferrous cylindrical wall ,
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 OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH