We listen and then say, "Yes, that is a certain bell ringing in the neighboring village," as if this were the most simple thing in the world. But why should one piece of metal striking against another a mile or two away make us aware that there is a bell there at all, let alone that it is a certain bell whose tone we recognize? Or we pass our fingers over a piece of cloth and decide, "That is silk." But why, merely by placing our skin in contact with a bit of material, should we be able to know its quality, much less that it is cloth and that its threads were originally spun by an insect? Or we take a sip of liquid and say, "This milk is sour." But why should we be able by taking the liquid into the mouth and bringing it into contact with the mucous membrane to tell that it is milk, and that it possesses the quality which we call _sour_? Or, once more, we get a whiff of air through the open window in the springtime and say, "There is a lilac bush in bloom on the lawn." Yet why, from inhaling air containing particles of lilac, should we be able to know that there is anything outside, much less that it is a flower and of a particular variety which we call lilac? Or, finally, we hold a heated flatiron up near the cheek and say, "This is too hot! it will burn the cloth." But why by holding this object a foot away from the face do we know that it is there, let alone knowing its temperature? THE UNITY OF SENSORY EXPERIENCE.--Further, our senses come through experience to have the power of fusing, or combining their knowledge, so to speak, by which each expresses its knowledge in terms of the others. Thus we take a glance out of the window and say that the day looks cold, although we well know that we cannot see _cold_. Or we say that the melon sounds green, or the bell sounds cracked, although a _crack_ or _greenness_ cannot be heard. Or we say that the box feels empty, although _emptiness_ cannot be felt. We have come to associate cold, originally experienced with days which look like the one we now see, with this particular appearance, and so we say we see the cold; sounds like the one coming from the bell we have come to associate with cracked bells, and that coming from the melon with green melons, until we say unhesitatingly that the bell sounds cracked and the melon sounds green. And so with the various senses. Each gleans from the world its own particular bit of knowledge, but all are finally in a partnership and what is each one's knowledge belongs to every other one in so far as the other can use it.