  We study large gauge transformations for soft photons in quantum
electrodynamics which, together with the helicity operator, form an ISO(2)
algebra. We show that the two non-compact generators of the ISO(2) algebra
correspond respectively to the residual gauge symmetry and its electromagnetic
dual gauge symmetry that emerge at null infinity. The former is helicity
universal (electric in nature) while the latter is helicity distinguishing
(magnetic in nature). Thus, the conventional large gauge transformation is
electric in nature, and is naturally associated with a scalar potential. We
suggest that the electric Aharonov-Bohm effect is a direct measure for the
electromagnetic memory arising from large gauge transformations.
