The organ must be either the body entire or some member set apart for a particular function; thus touch for one, vision for another. The tools of craftsmanship will be seen to be intermediaries between the judging worker and the judged object, disclosing to the experimenter the particular character of the matter under investigation: thus a ruler, representing at once the straightness which is in the mind and the straightness of a plank, is used as an intermediary by which the operator proves his work.
Some questions of detail remain for consideration elsewhere: Is it necessary that the object upon which judgement or perception is to take place should be in contact with the organ of perception, or can the process occur across space upon an object at a distance? Thus, is the heat of a fire really at a distance from the flesh it warms, the intermediate space remaining unmodified; is it possible to see colour over a sheer blank intervening between the colour and the eye, the organ of vision reaching to its object by its own power?
For the moment we have one certainty, that perception of things of sense belongs to the embodied soul and takes place through the body.
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