(11) Close your eyes, (_a_) Let an experimenter draw a blunt-pointed pencil _at an even rate_ along the inside of your arm from the shoulder to the tip of the middle finger. The point seems to travel more quickly at some places than at others: why? Draw a diagram of the arm, and mark the places of apparent slowing and quickening. (_b_) Tie two pencils together with a bit of rubber between, so that the points are 1-1/4 to 1-1/2 in. apart. Let an experimenter set the two points crosswise on the skin at the shoulder, and draw them with even speed and pressure along the inside of your arm to the finger-tips. The points seem to converge and diverge: why? Draw a diagram as before. (12) If a rough thread is drawn by an experimenter between your forefinger and thumb, at first quickly and then slowly, it will seem shorter in the first experiment than in the second. Why? References J. M. Charcot, Clinical Lectures on Diseases of the Nervous System, iii., 1889, Lect. xiii.; W. James, Principles of Psychology, 1890, i., chs. xiii., xv.; ii., chs. xviii., xix., xx.; C. H. H. Parry, The Evolution of the Art of Music, 1896; article on Optical Illusions, in Dictionary of Philosophy and Psychology, ii., 1902; W. Wundt, Lectures on Human and Animal Psychology, 1896, Lect. xi.; Outlines of Psychology, 1907, §§ 9, 10, 11; M. R. Fernald, The Diagnosis of Mental Imagery, 1912; E. B. Titchener, Experimental Psychology, I., i. and ii., 1901 (experiments on perception); Text-book of Psychology, 1910, 303 ff. CHAPTER VI ASSOCIATION Here is a kind of attraction which in the mental world will be found to have as extraordinary effects as in the natural, and to show itself in as many and as various forms.—DAVID HUME