hardness, smoothness, roughness, motion, rest, distance, and figure. Now it seems very easy to conceive, that these, with their several varieties, may impress corresponding varieties of vibrations upon the nerves of feeling; also, that these last varieties will be chiefly compositions of the vibrations arising from pressure, and muscular contraction, i.e. from the vis inertiæ of matter.
Thus, since moist bodies adhere to the fingers, and so leave a smoothness with their own degree of cold or heat upon them, moisture may be judged of by the touch from this peculiar alteration of vibrations; and dryness from the absence of it. Liquid bodies make no alteration of figure in our fingers, and yield easily to their motions: soft ones do the same in a less degree; hard ones the contrary. Smooth bodies make an equable pressure, and give no resistance to a motion along their surfaces; rough ones the contrary. The motions of our own bodies are attended by the vibrations peculiar to pressure, and muscular contraction; of other bodies which touch our own, by those from pressure. We judge of rest by the absence of these. Distance is judged of by the quantity of motion, and figure by the relative quantity of distance. And thus it appears, that all degrees and kinds of these tangible qualities may impress corresponding vibrations upon those regions of white medullary substance of the brain, and spinal marrow, which correspond to the skin and muscles.
The same qualities are made also by means of light to impress vibrations upon our eyes, which correspond in great measure to those made on the sense of feeling, so as to vary with their varieties. And as the sense of sight is much more extensive and expedite than feeling, we judge of tangible qualities chiefly by sight; which therefore may be considered, agreeably to Bishop Berkley’s remark, as a philosophical language for the ideas of feeling; being, for the most part, an adequate representative of them, and a language common to all mankind, and in which they all agree very nearly, after a moderate degree of experience.
However, if the informations from touch and sight disagree at any time, we are always to depend upon touch, as that which, according to the usual ways of speaking on these subjects, is the true representation of the essential properties, i.e. as the earnest and presage of what other tangible impressions the body under consideration will make upon our feeling in other circumstances; also what changes it will produce in other bodies; of which again we are to determine by our feeling, if the visual language should not happen to correspond to it exactly. And it is from this difference that we call the touch the reality, light the representative: also that a person born blind may foretell with certainty, from his present tangible impressions, what others would follow upon varying the circumstances; whereas if we could
