????? ??? ?? ??? ???? ??????? ?????. ????? ??? ?? ??? ???? ????? ???? ???????? ?????????. ???? ????? ??? ??????? ?????? ??????? ???????? ?????. ????? ??? ????????? ???????? ???????? ??????????? ?????? ??????? ???? ???????? ?????? ????? ??????.The 1st steel detector was possible The straightforward electric conduction steel detector ca. 1830.[41] El