_F_ (60) +116.45 116.45 17.14 - 36.06 36.30 6.29
_J_ (20) +174.30 174.63 30.94
Average: +170.53 174.69 30.66


The errors which appear in these tables are not consistently of the
type presented in the well-known rotation of visual planes
subjectively determined under conditions of abnormal relations of the
head or body in space. When the head is rotated upward on its lateral
horizontal axis the average location of the subjective horizon,
though still depressed below the true objective, is higher than when
rotation takes place in the opposite direction. When the whole body is
rotated backward through 45° a positive displacement of large amount
takes place in the case of all observers. When the rotation extends to
90°, the body now reclining horizontally but with the head supported
in a raised position to allow of free vision, an upward displacement
occurs in the case of one of the two observers, and in that of the
other a displacement in the opposite direction. When change of
position takes place in the head only, the mean variation is decidedly
greater if the rotation be upward than if it be downward, its value in
the former case being above, in the latter below that of the normal.
When the whole body is rotated backward through 45° the mean variation
is but slightly greater than under normal conditions; when the
rotation is through 90° it is much less. A part of this reduction is
probably due to training. In general, it may be said that the
disturbance of the normal body relations affects the location of the
subjective horizon, but the specific nature and extent of this
influence is left obscure by these experiments. The ordinary movements
of eyes and head are largely independent of one another, and even when
closed the movements of the eyes do not always symmetrically follow