Physical realism is the view that sense qualities are neither conscious states nor modes of the external universe, but modes or states of the perceiver's organism. It is favored by many scientists. Since nothing external can be immediately apprehended, but only inferred (by the principle of similarity) from data that are internal, we can ascertain the real nature of these latter data only by asking ourselves from what kind of data can we have inferred the objects which science assures us to be externally real. Such data must be internal but also physical, i.e. of the same order as the objects inferred by science. They cannot be purely psychic states. But the only objects which science assures us to be externally real are extension, volume, shape, motion, etc., which are like their internal sensible correlates, and such transcendentally inferred imperceptible modes of the former as e.g. corpuscles, undulations of aether, etc.: that correspond externally to the internal secondary qualities. And the reason why the former externals are like their internal correlates, and the latter unlike theirs, must be because the perceiver's sense organon is so constituted that it is capable of assuming in itself, and presenting to consciousness, states similar to the primary externals under the influence of the latter, whereas it can assume and present to consciousness under the influence of the secondary externals only states dissimilar to these. (Vol. 2, p.124-5).
Coffey sees no sufficient grounds for this view, for example, external motion is like sensible motion, but external heat is an imperceptible mode of motion while sensible heat is not sensibly a motion at all. He objects to the motion example considering the motion of a train or hailstorm saying that the internal, sensible appearance is an immediately apprehended nerve motion or organic condition appearing as an external train or hailstorm motion. (I don't buy his argument there when I consider the co-occurring retinal image.) (Vol. 2, p.126-7).
A little later, he expresses his objection as follows: "For since the whole sense organon is an extramental material factor, we cannot say that it presents to conscious one set of qualities as they are--whether in itself or in the extra-organic domain, or partly in the one and partly in the other, but in both cases--beyond or independently of consciousness, and another set otherwise than they are beyond or independently of consciousness" (Vol. 2, p.133).