or I for vacuum 真空 matter s1 or paramagnetic subs tance顺磁质 < I for diamagnetic subs tance抗磁质 (1 for ferromagnetic subs tance铁磁质        =  for ferromagne tic substance for diamagneti c substance for paramagneti c substance for vacuum  r or 真空 顺磁质 抗磁质 铁磁质 matter