Electromagnetism : 1820 . . 100 1820 ǡ ǡ ɡ ʡ ɡ . . ѡ ǡ . 1777 ߡ ɡ John Ritter Urkraft . ɡ ߡ 1800 1820 80 ɡ ʡ . . ǡ ߡ . ϡ 3 ѡ ǡ . ɡ ɡ ߡ ѡ... .