thus to refer one's sensations to an external object is to be able to
perceive objects.

=Fulness of Perception Based on Sensation.=--From the foregoing account
of the development of our perception of the external world, it becomes
evident that our immediate knowledge, or idea, of an individual object
will consist only of the images our senses have been able to discover
either in that or other similar objects. To the person born without the
sense of sight, for instance, the flower-bed can never be known as an
object of tints and colours. To the person born deaf, the violin cannot
really be known as a _musical_ instrument. Moreover, only the person
whose senses distinguish adequately variations in colour, sound, form,
etc., is able to perceive fully the objects which present themselves to
his senses. Even when the physical senses seem equally perfect, one man,
through greater power of discrimination, perceives in the world of
objects much that totally escapes the observation of another. The result
is that few of us enter as fully as we might into the rich world of
sights, sounds, etc., with which we are surrounded, because we fail to
gain the abundant images that we might through certain of our senses.

FACTORS INVOLVED IN SENSATION

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.

3. The organ of sense--the ear.

[Illustration]

4. The nerves--cells and fibres involved in receiving and conveying the
sense stimulus.

5. The interpreting cells.

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