  In 1861, Maxwell derived two of his equations of electromagnetism by
modelling a magnetic line of force as a `molecular vortex' in a fluid-like
medium. Later, in 1980, Berry and colleagues conducted experiments on a `phase
vortex', a wave geometry in a fluid which is analogous to a magnetic line of
force and also exhibits behaviour corresponding to the quantisation of magnetic
flux. Here we unify these approaches by writing down a solution to the
equations of motion for a compressible fluid which behaves in the same way as a
magnetic line of force. We then revisit Maxwell's historical inspiration,
namely Faraday's 1846 model of light as disturbances in lines of force. Using
our unified model, we show that such disturbances resemble photons: they are
polarised, absorbed discretely, obey Maxwell's full equations of
electromagnetism to first order, and quantitatively reproduce the correlation
that is observed in the Bell tests.
