_E._ (20) +79.30 79.30 11.56 +131.67 131.67 12.07
_H._ (10) -37.50 37.50 16.80 -46.90 46.90 7.90
_K._ (30) +71.40 71.40 12.85 +48.05 48.05 5.11
Average: +33.00 51.75 11.61 +41.95 65.43 8.34


The introduction of a descending plane lowers the apparent horizon;
that of an ascending plane elevates it. The general disturbance of
judgment appears distinctly greater in the case of a downward than in
that of an upward incline.

The results of a third variation of the experimental conditions may be
presented at once. In it the location of the subjective horizon under
normal conditions was compared with the results of adjustments made
when the screen bearing the white disc was rotated backward from the
observer through an angle of varying magnitude. The averages for each
of the two subjects are as follows:


TABLE XIII.

Observer Const. Err. Av. Dev. Mean Var. Rotation.
_F_ (20) +130.50 130.50 3.20 20°
" " +115.50 115.50 1.10 50°
_J_ (20) +443.10 443.10 9.47 45°


These experiments were carried on in the presence of the definitely
figured visual field of the lighted room, and the observers were
conscious of taking these permanent features into account as