1. _We determine our perpendicularity by the apparent motions of
objects. A person hood-winked cannot walk in a straight line. Dizziness
in looking from a tower, in a room stained with uniform lozenges, on
riding over snow._ 2. _Dizziness from moving objects. A whirling-wheel.
Fluctuations of a river. Experiment with a child._ 3. _Dizziness from
our own motions and those of other objects._ 4. _Riding over a broad
stream. Sea-sickness._ 5. _Of turning round on one foot. Dervises in
Turkey. Attention of the mind prevents slight sea-sickness. After a
voyage ideas of vibratory motions are still perceived on shore._ 6.
_Ideas continue some time after they are excited. Circumstances of
turning on one foot, standing on a tower, and walking in the dark,
explained._ 7. _Irritative ideas of apparent motions. Irritative ideas
of sounds. Battèment of the sound of bells and organ-pipes. Vertiginous
noise in the head. Irritative motions of the stomach, intestines, and
glands._ 8. _Symptoms that accompany vertigo. Why vomiting comes on in
strokes of the palsy. By the motion of a ship. By injuries on the head.
Why motion makes sick people vomit._ 9. _Why drunken people are
vertiginous. Why a stone in the ureter, or bile-duct, produces
vomiting._ 10. _Why after a voyage ideas of vibratory motions are
perceived on shore._ 11. _Kinds of vertigo and their cure._ 12.
_Definition of vertigo._

1. In learning to walk we judge of the distances of the objects, which we
approach, by the eye; and by observing their perpendicularity determine our
own. This circumstance not having been attended to by the writers on
vision, the disease called vertigo or dizziness has been little understood.

When any person loses the power of muscular action, whether he is erect or
in a sitting posture, he sinks down upon the ground; as is seen in fainting