Children whose parents have little theoretic knowledge of the values of the various food-stuffs are often thoroughly nourished; their parents rely on what they call common-sense; and the result is, on the whole, better than if scientific consideration were given to the family dietary. But this common-sense has usually scientific opinion for its basis, though the fact may be forgotten, and when scientific opinion has become the groundwork of habit it is of more value, and works in a more simple way, than while it is still in the stage of experiment. In the same way it is a good thing to have such an acquaintance with the functions of human nature that we act on our knowledge unconsciously, and do not even know that we possess it. But if we have no such floating capital of cognisance we must study the subject, even if we have to make experiments. Most people suppose that the sensations, feelings, and emotions of a child are matters that take care of themselves. Indeed, we are apt to use the three terms indiscriminately, without attaching very clear ideas to them. But they cover, collectively, a very important educational field; and though common sense, that is to say judgments formed upon inherited knowledge, often helps us to act wisely without knowing why, we shall probably act more wisely if we act reasonably. Let us consider, first, the subject of sensations. We speak of sensations of cold, and sensations of heat, and sensations of pain, and we are quite right. We also speak of sensations of fear and sensations of pleasure, and we are commonly wrong. The sensations have their origin in impressions received by the several organs of sense--eye, tongue, nostrils, ear, the surface of the external skin--and are conveyed by the sensory nerves, some to the spinal cord and some to the lower region of the brain. Many sensations we know nothing about; when we become aware of our sensations it is because communications are sent by nerve fibres, acting as telegraph wires, from the sensorium to the thinking brain, and this happens when we give our _attention_ to any one of the multitudinous messages carried by the sensory nerves. The physiology of the senses is too complicated a subject for us to touch upon here, but it is deeply interesting, and perhaps no better introduction exists than Professor Clifford’s little book, “Seeing and Thinking” (Macmillan). Now the senses are “The Five Gateways of Knowledge,” to quote the title of a little book which many of us have used in early days; and an intelligent person should be aware of, and capable of forming judgments upon, the sensations he receives.