An elementary discussion is given regarding the momentum associated with a photon in a dispersive medium. The results of the Jones-Richards (1954) and the Jones-Leslie (1978) experiments are taken to confirm that, if the momentum of the photon in vacuo is p, the total momentum associated with the same photon in a dispersive medium of phase refractive index nϕ is nϕp (as the Minkowski energy-momentum tensor would imply). It is then argued that a portion p/ng of this momentum may be regarded as ‘electromagnetic’ (pace the Abraham tensor) and the remainder nϕp(1 — 1/nϕng) as ‘mechanical’ and bodily present in the medium, where nϕ is the ‘group refractive index’. This leads to plausible results for an artificial dielectric where nϕng = 1, and suggests an element of reciprocity between the ‘drag’ of light on the medium through which it is passing and the ‘aether drag ’ of a moving medium on light, since the drag coefficient (1 — 1/nϕng)enters into both cases.
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R V Jones (1978) studied this question.