Published online by Cambridge University Press: 12 April 2016
In order to determine the sense of the photospheric transverse magnetic field measured with a magnetograph, it is shown that: (1) If the magnetic lines of force through the photospheric plane are both divergent and convex upward, Krall’s criterion
is true for the transverse field B⊥ much more strongly than for the longitudinal field Bz and the inequality in general becomes
(2) If the magnetic lines of force are only divergent upward, we have instead the inequality
for a force-free field.