s not been
accustomed to balance himself by objects placed at such distances and with
such inclinations, begins to stagger, and endeavours to recover himself by
his muscular feelings. During this time the apparent motion of objects at a
distance below him is very great, and the spectra of these apparent motions
continue a little time after he has experienced them; and he is persuaded
to incline the contrary way to counteract their effects; and either
immediately falls, or applying his hands to the building, uses his muscular
feelings to preserve his perpendicular attitude, contrary to the erroneous
persuasions of his eyes. Whilst the person, who walks in the dark,
staggers, but without dizziness; for he neither has the sensation of moving
objects to take off his attention from his muscular feelings, nor has he
the spectra of those motions continued on his retina to add to his
confusion. It happens indeed sometimes to one landing on a tower, that the
idea of his not having room to extend his base by moving one of his feet
outwards, when he begins to incline, superadds fears to his other
inconveniences; which like surprise, joy, or any great degree of sensation,
enervates him in a moment, by employing the whole sensorial power, and by
thus breaking all the associated trains and tribes of motion.

7. The irritative ideas of objects, whilst we are awake, are perpetually
present to our sense of sight; as we view the furniture of our rooms, or
the ground, we tread upon, throughout the whole day without attending to
it. And as our bodies are never at perfect rest during our waking hours,
these irritative ideas of objects are attended perpetually with irritative
ideas of their apparent motions. The ideas of apparent motions are always
irritative ideas, because we never attend to them, whether we attend to the
objects themselves, or to their real motions, or to neither. Hence the
ideas of the apparent motions of objects are a complete circle of
irritative ideas, which continue throughout the day.

Also during all our waking hours, there is a perpetual confused sound of
various bodies, as of the wind in our rooms, the fire, distant
conversations, mechanic business; this continued buzz, as we are seldom
quite motionless, changes its loudness perpetually, like the sound of a
bell; which rises and falls as long as it continues, and seems to pulsate
on the ear. This any one may experience by turning himself round near a
waterfall; or