_Abstraction_ is the power of noticing certain parts or qualities of any object, as distinct from other parts or qualities. Thus, when we notice the length of a bridge without attending to the breadth or color, or when we notice the height of a man without thinking of his character, we exercise the faculty of abstraction.
_Attention_ is the direction of the mind to any particular object or quality, from the interest which is felt in it, or in something connected with it. The degree of attention is always proportioned to the degree of interest felt in the object.
_Association_ is the power possessed by the mind of recalling ideas in the connections and relations in which they have existed in past experience. For example, when any two objects, such as a house and a tree, have often been observed together, the idea of one will ordinarily be attended by that of the other. If two events have often been united together in regard to the _time_ of their occurrence, such, for example, as thunder and lightning, the idea of one will usually be attended by the other.
In this work, the aim is to introduce no more of mental analysis than is needed for its main object. What is here introduced is not claimed as a complete presentation of all the mental phenomena.
As there is no distinction between sensation and perception except in the fact that one is attended with the belief of a cause and the other is not, they will be treated of together.
The mind of man is an immaterial existence, confined in its operations by the body it inhabits, and depending upon the construction and modifications of this envelope for much of its happiness or suffering.
The exercise of the imagination, when the eyes are closed and the body at rest, will probably give us the best idea of what is the nature of spiritual existence when disconnected with matter. It is one of the offices of our bodily system to retain the spirit in its operations in one particular place, so that ordinarily it can have direct communion with no other mind which is not in the same place. Whether this is the case with mere spiritual existence is a question for conjecture, and not for any rational decision.
While the spirit of man is resident in its material frame, it is furnished with facilities of communication with other minds, and with organs which fit it to receive suffering or enjoyment from the material objects by which it is surrounded. These organs of communication are the several senses. They consist of expansions of the substance of which the brain is formed, which, descending to the body through the spinal bone of the back, are thence sent out in thousands of ramifications over the whole system. Those branches which enter the eyes, and are spread over the interior back part of this organ, are called the _optic nerve_. Whenever the particles of light enter the eye, they strike the optic nerve, and produce the sensation which is called _sight_. Those branches which are spread over the tongue are the organ of _taste_. Those that are extended through the cavities of the nostrils are called the _olfactory_ nerves. When the small particles of matter that escape from odoriferous bodies come in contact with these nerves, they produce the sensation of _smell_.