Passing to a consideration of the senses as organs through which the mind is made aware of the concrete world, it is to be noted that a number of factors precede the image, or mental interpretation, of the impression. When, for instance, the mind becomes cognizant of a musical note, an analysis of the whole process reveals the following factors:
1. The concrete object, as the vibrating string of a violin.
2. Sound waves proceeding from the vibrating object to the sense organ.
4. The nerves--cells and fibres involved in receiving and conveying the sense stimulus.
6. The reacting mind, which interprets the impression as an image of sound.
The different factors are somewhat arbitrarily illustrated in the accompanying diagram, the arrows indicating the physical stimulation and the conscious response:
Of the six factors involved in the sensation, 1 and 2 are purely physical and belong to the science of acoustics; 3, 4, and 5 are physiological; 6 is conscious, or psychological. It is because they always involve the immediate presence of some physical object, that the sensation elements involved in ordinary perception are spoken of as immediate, or presentative, elements of knowledge.
Our various sensations are usually divided into three classes as follows:
1. Sensations of the special senses, including: sight, sound, touch (including temperature), taste, and smell.
=Sensations of the Special Senses.=--As a study of the five special senses has been made by the student-teacher under the heading of physiology, no attempt will be made to explain the structure of these organs. It must be noted, however, that not all senses are equally capable of distinguishing differences in quality. For example, it seems quite beyond our power to recall the tastes and odours of the various dishes of which we may have partaken at a banquet, while on the other hand we may recall distinctly the visual appearance of the room and the table. It is worthy of note, also, that in the case of smell, animals are usually much more discriminative than man. Certain of our senses are, therefore, much more intellectual than others. By this is meant that for purposes of distinguishing the objects themselves, and for providing the mind with available images as materials for further thought, our senses are by no means equally effective. Under this heading the special senses are classified as follows: