BILATERAL ASYMMETRY OF FUNCTION. 107 uniformly highest in position I., and likely to be so in ILT. Though our data comprise many thousand records, they wan-ant no inference which hand is farthest front in II. The individual error here is constant, but bears no relation yet discernible to either right- or left-handedness, or to relative eccentricity of localisation. In another series of records (IV.), the fingers were both moved in the median plane in front, one upward, the other downward. Here the same finger was outermost as before, and there was also generally a slight tendency to overlap, but which hand, if either, tended more strongly to cross the plane into the dominion of the other, has not yet been determined. The devia- tions of a conjectured median plane, thus determined from an exact geometrical one, would no doubt be as great, and as hard to determine, as the difference also known to exist between the mathematical and the empirical horopter ; failure to come quite round to the same vertical plane was constant in none of our subjects. If, finally, the contact was made by bringing one hand well round into the domain of the other (V.), the approxima- tions were less accurate than if made in the median plane. These movements are a little, but only a little, more accurate in front, where the volitional action of the hand is usually guided by the eyes, than above the head and behind. If we could determine the farthest possible point in each direction, and for each position of the joints, amount of pronation, supination, etc., that could be touched with each index finger, a constant primary position of the body being of course assured, and the effects of fatigue upon the form of such a surface being eliminated ; if we could then construct, within this surface, other iso-potential surfaces repre- senting the angular translocating power of each arm straight and with different degrees of flexion ; if through these surfaces we could construct lines of greatest and least flexion-power, &c. we should have not merely a record of the mechanical properties of the frame- work of the arm, but superimposed upon this common element would be differences between persons and each arm of the same person, which would represent his and its entire motor-history and expeiience ; causing endless variation in the lines of easiest, hardest, swiftest motion, position when at rest, muscle-sense and judgment, &c., and giving distinct individual habit and char- acter to each limb, muscle and centre of motor innervation, which, even when trained, not only in skilful but in pretty equal use of the hands, we fail to know and compensate for without the use of the eye. D. An extended series of reaction-times was measured for the four persons under observation, two of whom were right- and two left-handed, with an arrangement of apparatus similar to that described by Vundt (Pkyigiologucke Pt?ydir>Jor)i*>, Bd. II., s. 231), for which we were indebted to the kindness of Mr. C. S. Peirce, and which was used as follows. The hearing power of each ear being found to be about normal and equal, both were equally
