The observer sat with the light at his back, and by manipulation of the cords adjusted the position of the white disc freely up and down the screen until its center was judged to be on a level with the eye. Its position was then read off the vertical scale by the conductor (who sat hidden by an interposed screen), and the error of judgment was recorded in degrees and fractions as a positive (upward) or negative (downward) displacement. The disc was then displaced alternately upward and downward, and the judgment repeated. From the time of signalling that the point had been located until this displacement the observer sat with closed eyes. These determinations were made in series of ten, and the individual averages are in general based upon five such series, which included regularly the results of sittings on different days. In some cases twice this number of judgments were taken, and on a few occasions less. The number of judgments is attached to each series of figures in the tables. In that which follows the individual values and their general averages are given as minutes of arc for (a) the constant error or position of the subjective horizon, (b) the average deviation from the objective horizon, and (c) the mean variation of the series of judgments.
Observer. Constant Error. Average Deviation. Mean Variation. A (100) -19.74 38.78 10.67 C (90) -18.18 23.89 10.82 D (100) -19.84 33.98 7.95 E (50) — 4.28 72.84 6.90 F (100) +46.29 46.29 2.05 G (50) +14.96 35.40 8.40 H (50) -27.22 27.46 5.78 I (50) + 6.62 53.34 7.45 K (50) + 1.08 30.26 6.59 L (20) -56.70 56.70 10.39
Average: -7.70 41.89 7.69
The average subjective horizon shows a negative displacement, the exceptional minority being large. No special facts could be connected with this characteristic, either in method of judgment or in the past habits of the reactor. The average constant error is less than an eighth of a degree, and in neither direction does the extreme reach the magnitude of a single degree of arc. Since the mean variation is likewise relatively small, there is indicated in one’s ordinary judgments of this kind a highly refined sense of bodily orientation in space.