Apparatus: A disc (Fig. 1, Plate IX.) about 50 c. in diameter, rotating on a vertical pivot, was driven by a pulley-cone underneath mounted on the same spindle (not shown in the figure). On the face of the disc were four concentric rings of regularly spaced holes, which received pegs of uniform height and provided with a shoulder. Corresponding holes of each circle lay on the same radius. On a plate supported by a bracket were mounted four levers whose heads stood in line radially to the movable disc. When the disc rotated to the right under the levers, the pegs forced up the lever heads and made an electric contact. The dip of the levers was controlled by a screw adjustment. The apparatus was driven by a motor and reducing gear, which were isolated in a sound-proof box. The rate of speed was controllable.
The apparatus was built for use with sounders connected with the binding-posts, but in this investigation sounders were dispensed with, and the clicks from the apparatus itself were used, since but one qualitative difference was introduced. As a rule, the objective accent of the foot was not given; the subjective accentuation was nearly always sufficient. Subjects were quite unable to say whether the accent was objective or not. If necessary, an accentuation was produced by raising the pegs representing the accentuated part of the foot. The group elements were represented by single, simple clicks made by a brass screw on the lever arm striking an iron plate (the noise of the brass peg striking the lever head was eliminated by damping with cloth). The rhyme was represented by a compound noise consisting of a click higher in pitch than the verse element click, made by the peg striking the lever head, and an almost simultaneous click lower in pitch than the verse element click, made by the screw of the lever arm striking another iron plate. The rhyme noise was not louder than the verse element click, and as a whole gave the impression of being a lower tone because the first click was very brief. Subjects did not analyze the rhyme noise, and had no difficulty in making it represent rhyming syllables. The pauses throughout had no filling.
The subject was always given a normal series until the type was clearly established, and when the variations to be judged were introduced his attention was directed as far as possible to the factor to be introduced. This seemed the only way to obtain trustworthy judgments. If the subject waits blindly for some perceptual change in the whole complicated mass of sensations which the simplest rhythmic series constitutes, he is apt to fit his attention on some irrelevant detail, and the change may not be noted until greatly exaggerated, and he may not judge that particular factor at all.