Each channel of sense impressions has an organ, or organs, peculiarly adapted for the excitation of its substance by the particular kind of vibrations through which it receives impressions. The eye is most cunningly and carefully designed to receive the light-waves; and sound-waves produce no effect upon it. And, likewise, the delicate mechanism of the ear responds only to sound-waves; light-waves failing to register upon it. Each set of sensations is entirely different, and the organs and nerves designed to register each particular set are peculiarly adapted to their own special work. The organs of sense, including their special nervous systems, may be compared to a delicate instrument that the mind has fashioned for itself, that it may investigate, examine and obtain reports from the outside world. We have become so accustomed to the workings of the senses that we take them as a "matter of course," and fail to recognize them as the delicate and wonderful instruments that they are--designed and perfected by the mind for its own use. If we will think of the soul as designing, manufacturing and using these instruments, we may begin to understand their true relations to our lives, and, accordingly treat them with more respect and consideration. We are in the habit of thinking that we are aware of all the sensations received by our mind. But this is very far from being correct. The unconscious regions of the mind are incomparably larger than the small conscious area that we generally think of when we say "my mind." In future lessons we shall proceed to consider this wonderful area, and examine what is to be found there. Taine has well said, "There is going on within us a subterranean process of infinite extent; its products alone are known to us, and are only known to us in the mass. As to elements, and their elements, consciousness does not attain to them. They are to sensations what secondary molecules and primitive molecules are to bodies. We get a glance here and there at obscure and infinite worlds extending beneath our distinct sensations. These are compounds and wholes. For their elements to be perceptible to consciousness, it is necessary for them to be added together, and so to acquire a certain bulk and to occupy a certain time, for if the group does not attain this bulk, and does not last this time, we observe no changes in our state. Nevertheless, though it escapes us, there is one." But we must postpone our consideration of this more than interesting phase of the subject, until some future lesson, when we shall take a trip into the regions of Mind, under and above Consciousness. And a most wonderful trip many of us will find it, too. For the present, we must pay our attention to the channels by which the material for knowledge and thought enter our minds. For these sense impressions, coming to us from without, are indeed "material" upon which the mind works in order to manufacture the product called "Thought."