Lines of topological singularity in the phase and polarization of light
are being intensively studied now,1 motivated in part by a theoretical paper
published thirty years ago.2 However, the subject has a very long prehistory,
that is not well known.
In puzzling over Grimaldi's observations of edge diffraction in the 1660s,
Isaac Newton narrowly missed discovering phase singularities in light. The
true discovery of phase singularities was made by William Whewell3 in
1833, not in light but in the pattern of ocean tides. The first polarization
singularity was observed (but not understood) by Arago in 1817, in the
pattern of polarization of the blue sky. A different polarization singularity
was predicted by Hamilton in the 1830s, in the optics of transparent biaxial
crystals (this was also the first 'conical intersection' in physics).