Hft. 5) misunderstood or misread parts of the original paper; and the present remarks are mainly directed towards the correction of his article. The question at issue is an important one, and has hardly as yet received a final answer. (2) Zu Franz Brentano's "Ueber ein optisches Paradoxon." The fact of the over- and under- estimation of distance in certain cases of optical illusion was explained by Brentano (Bd. III, Hft. 5) by the over- and under-estimation of large angles. Lipps points out, in an acute paper, that this explanation is not adequate; and that, even if adequate, it would not necessarily exclude the operation of other factors. He himself regards the illusions as dependent on the idea of a free or inhibited movement along the lines bounding the figures. The view is set forth at length in his Aesthetische Faktoren der Raumanschauung (Helmholtz’ Festschrift). Systematic experimentation would seem to be the only method by which certainty can be attained in this vexed chapter of psychological optics.
The research aimed to determine the time of making three hundred taps from the wrist on a Morse key, together with some conditions influencing the rate. A kymograph was used with a revolving drum on which the seconds were registered by means of the armature of an electro-magnet. On the same standard with the magnet was fastened a clock movement whose escapement wheel turned one notch with each tap of the key. Six tests of three hundred taps each were made at intervals of two hours from 8 A.M. to 6 P.M. After six weeks of work a daily rhythm was developed with the slowest rate at 8 A.M., the most rapid rate at 4 P.M., and a falling off at 2 P.M. and at 6 P.M. The curve representing a daily record corresponded to the programme of public school work in which the subject had for two years been engaged, beginning at 8 A.M. and closing at 4 P.M. with an hour and a half intermission. The activity of the central nervous system probably increased during the hours of work, lessened during the noon hour of relaxation, and again decreased after four o'clock, when the chief work of the day was over. The short walk to dinner had no effect, but a vigorous walk caused falling off in the rate, due probably to general fatigue and mental relaxation. Strong mental concentration and interest favored rapidity of movement. The effect of a day of rest was very slightly unfavorable. No effect of atmospheric pressure could be detected. The normal rate for the right wrist averaged 8.5 taps per second.
