ects or circumstances
which are indifferent, and afford less delight. But the very
constitution of our nature limits our enjoyments, and points out the
impossibility of perpetual pleasures in this state of our existence.
To a person who is thirsty, water is delicious nectar; to one who is
hungry, every kind of food is agreeable, and even its smell pleasant;
to a person who is hot and feverish, the cool air is highly
refreshing. But to the same persons in different circumstances, the
same things are not only indifferent, but even disgusting; for
instance, a person cannot bear the sight or smell of food, after
having satiated himself with it, and perpetual feasting will cloy the
appetite of the keenest epicure.

I shall conclude this account of the general laws of sensation, by a
short recapitulation of those laws.

And, in the first place, it may be observed, that the energy or force
of any sensation, is proportioned to the degree of attention given by
the mind to the external object which causes it.

Secondly, A repetition of sensations diminishes their energy, and at
last nearly destroys it; but this energy is restored by rest, or the
absence of these sensations.

Thirdly, The mind cannot attend to two impressions at the same time:
so that two sensations never act with the same force at the same
instant; the stronger generally overcoming the weaker. The mind,
however, can attend to the weaker sensation, in such a manner, as to
overpower the stronger, or to render it insensible.

Having fully considered the general laws of sensation, I shall now
proceed to examine those proper to each sense; and in this
examination, two objects will engage our attention. 1. The structure
of the organ which receives and transmits the impulse to the mind. 2.
The qualities or properties of external bodies, particularly those by
which they are fitted to excite sensation.

The first sense that we shall examine is touch, which, of all the
external senses, is the most simple, as well as the most generally
diffused. By means of this sense, we are capable of perceiving
various qualities and properties of bodies, such as hardness,
softness, roughness, smoothness, temperature, magnitude, figure,
distance, pressure, and weight; this sense is seldom depraved;
because the bodies, whose properties are examined by it, are applied
immediately to the extremities of the nerves, without the
intervention of any medium liable to be deranged, as is th