ular system; and pleasure is introduced
in consequence of these increased motions from internal stimulus. According
to Law 5. Sect. IV. on Animal Causation.

From this great increase of irritative motions from internal stimulus, and
the increased sensation introduced into the system in consequence; and
secondly, from the increased sensitive motions in consequence of this
additional quantity of sensation, so much sensorial power is expended, that
the voluntary power becomes feebly exerted, and the irritation from the
stimulus of external objects is less forcible; the external parts of the
eye are not therefore voluntarily adapted to the distances of objects,
whence the apparent motions of those objects either are seen double, or
become too indistinct for the purpose of balancing the body, and vertigo is
induced.

Hence we become acquainted with that very curious circumstance, why the
drunken vertigo is attended with an increase of pleasure; for the
irritative ideas and motions occasioned by internal stimulus, that were not
attended to in our sober hours, are now just so much increased as to be
succeeded by pleasurable sensation, in the same manner as the more violent
motions of our organs are succeeded by painful sensation. And hence a
greater quantity of pleasurable sensation is introduced into the
constitution; which is attended in some people with an increase of
benevolence and good humour.

If the apparent motions of objects is much increased, as when we revolve on
one foot, or are swung on a rope, the ideas of these apparent motions are
also attended to, and are succeeded with pleasureable sensation, till they
become familiar to us by frequent use. Hence children are at first
delighted with these kinds of exercise, and with riding, and failing, and
hence rocking young children inclines them to sleep. For though in the
vertigo from intoxication the irritative ideas of the apparent motions of
objects are indistinct from their decrease of energy: yet in the vertigo
occasioned by rocking or swinging the irritative ideas of the apparent
motions of objects are increased in energy, and hence they induce pleasure
into the system, but are equally indistinct, and in consequence equally
unfit to balance ourselves by. This addition of pleasure precludes desire
or aversion, and in consequence the voluntary power is feebly exerted, and
on this account rocking young children inclines them to sleep.

In what manner opium and win