??? ??? ??? ?????????? ????? ????? ?????? ??? ???? ????? ?????? ?????? ????? ?? ???? ????? ?????? ?? ????? ???? ?????? ??? ?????? ???? ??? ??????? ?????? ??????????.The initial metallic detector was probably the simple electric conduction steel detector ca. 1830.[41] Electric conduction was also utilized to locate metallic ore bodies by measuring t