The position of eyes 0°. The right edge was moved, at first from an evident + position to equality, then from equality to the - threshold, then from an evident - position to equality, then from equality to the + threshold. These four points were determined each fifteen times and the average taken. Then exactly the same fifteen sets of four determinations with the left edge moved. The averages of these 120 experiments are these: When the left edge is moved from + to =:-2.77, from = to -:-6.97, from - to =:+0.77, from = to +5.93. When the right edge is moved from + to =: +2.83, from = to -:-1.6, from - to =:+5.9, from = to +:+10.53. The first equality-point appears thus when the left edge is moved at -0.76, when the right edge is moved at +4.41, with a threshold of about 5 in either case. With the normal eye-position the edges must thus not be exactly in the same plane to appear equally distant; at a distance of 2000 mm. the left must be about 2 mm. nearer than the right to appear in the same plane, vertical to the line of regard. If the position of the eyes is 15° to the left, we have the following results: When the left edge is moved from + to =:-4.17, from = to -:-8.5, from - to =:-1.33, from = to +:+1; when the right edge is moved from + to =:+4.17, from = to -:+1.17, from - to =:+4.5, from = to +:+8.67. If the position of the eyes is 30° to the left, we find when the left edge is moved from + to =:-2.67, from = to -:-6.67, from - to =:+0.5, from = to +:+3.33. When the right edge is moved from + to =:+2.33, from = to -:-0.02, from - to =:+9., from = to +:+12.33. If we take again the general averages, we have for the eye-position of 15° to the left an equality-point of -3.25 if the left edge is moved and judged and +4.63 if the right edge is moved and judged. That is, if the right edge stands at 2000 mm. the left edge must be moved to 1996.75, and if the left stands at 2000, the right must be moved to 2004.63. For the eye-position of 30° to the left, the equality-point lies at -1.49 if the left edge is moved and judged, and at +5.91 if the right edge is the variable. The threshold lies in all three cases, for eyes at 0°, at 15°, and at 30°, at about ±5 mm.; the position of the eyes has thus no influence on the threshold for the perception of distance in the direction of regard. But the point essential for our investigation is of course not the threshold but the equality-point. To take the extremes of the eye-positions 0° and 30° we find the equality when the left edge is judged, at -0.76 for 0° and -1.49 for 30°, and when the right edge is moved, at +4.41 at 0° and +5.91 at 30°; the middle is thus +1.82 for 0° and +2.21 for 30°, that is a difference of less than 0.4 mm.