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_. The nerves that constitute the organ of _hearing_ are extended over the cavity of the ear behind the _tympanum_, or _ear-drum_. This cavity is filled with a liquid, and when the drum of the ear is caused to vibrate by the air which is set in motion by sonorous bodies, it produces undulations of this liquid upon these nerves, and thus the sensation of _sound_ is produced. By the expansion of other nerves, the sense of _feeling_ is extended all over the body, excepting the nails and the hair. It is by the action of matter, in its different forms, on these several senses, that the mind obtains ideas, and that ideas are imparted from one mind to another. _Perception_ never takes place unless some material object makes an impression upon one of the senses. In the case of the eye, the ear, and the nostrils, the object which is regarded as the cause of the sensation does not come immediately in contact with the organs of sense. When we see a body, we consider it as the cause of that perception; but it is not the body that comes in contact with the organ of sight, but merely the particles of light reflected from that body. In the case of smell, the fragrant body is regarded as the cause of the sensation; but that which acts on the sense is the material particles of perfume which flow from that body.