198 w. JAMES :

When, by simply flexing my right forefinger on its meta- carpal joint, I trace with its tip an inch on the palm of my left hand, is my feeling of the size of the inch purely and simply a feeling in the skin of the palm, or have the muscu- lar contractions of the right hand and forearm anything to do with it ? In the preceding pages I have constantly assumed spatial sensibility to be an affair of surfaces. At first starting, the consideration of the " muscular sense " as a space-measurer was postponed to a later stage. Many writers, of whom the foremost was Thomas Brown, in his Lectures on the Philosophy of the Human Mind, and of whom the latest is no less a psychologist than Prof. Delboeuf of Liege, hold that the consciousness of active muscular motion, aware of its own amount, is the fons et origo of all spatial measure- ment. It would seem to follow, if this theory were true, that two skin-feelings, one of a large patch, one of a small one, possess their difference of spatiality, not as an immediate element, but solely by virtue of the fact that the large one, to get its points successively excited, demands more muscular contraction than the small one does. Fixed associations with the several amounts of muscular contraction required in this particular experience, would thus explain the apparent sizes of the skin-patches, which sizes would consequently not be primitive data but derivative results. It seems to me that no evidence of the muscular measure- ments in question exists ; but that all the facts may be explained by surf ace- sensibility, provided we take that of the joint-surfaces also into account. The most striking argument, and the most obvious one, which an upholder of the muscular theory is likely to pro- duce, is undoubtedly this fact : if, with closed eyes, we trace figures in the air with the extended forefinger (the motions may occur from the metacarpal-, the wrist-, the elbow- or the shoulder-joint indifferently), what we are conscious of in each case, and indeed most acutely conscious of, is the geometric path described by the finger-%>. Its angles, its subdivisions, are all as distinctly felt as if seen by the eye ; and yet the surface of the finger-tip receives no sensation at all. 1 But with each variation of the figure, the muscular contractions vary, and so do the feelings these yield. Are not these latter the sensible data that make us aware of the lengths and directions we discern in the traced line ? 1 Even if the figure be drawn on a board instead of in the air, the varia- tions of contact on the finger's surface will be much simpler than the peculiarities of the traced figure itself.