An exposition of the fundamental conception of chemical science will illustrate the nature of scientific faith. A fragment of almost any substance may easily be divided into two or three pieces by a stroke of a hammer. Each of the pieces may be broken into smaller pieces and this process of division continued until the powder is as fine as dust. Still, each particle of the dust may be divided again and again, if we only have instruments fine enough to continue the process. A question which philosophy asked itself near its beginning was: Is it possible to keep on dividing the dust particles forever, or is there a particle so small that it can not be divided again? Neither science nor abstract philosophy has yet been able to answer this question fully. However, science has learned that if such a process of division occurs, in course of time a particle will be obtained which is so small that if it is divided or broken, the fragments will no longer be of the same nature as the original substance. These smallest particles in which the properties of the original substance inhere, are known as _molecules._ Thus a molecule of sugar, when broken, falls into the elements carbon, hydrogen and oxygen; of salt, into sodium and chlorine and of water into hydrogen and oxygen. The size of such a molecule can not be comprehended by the human mind; its smallness seems infinite. The mortal eye, though aided by the most powerful miscroscopes of modern days could not distinguish a sugar molecule or even a pile of thousands of them; placed on the tongue, there would be no sensation of sweetness; though it were hurled against our body with the velocity of lightning we should not feel the impact. To all our senses, the molecule is wholly unknown and no doubt shall remain so while the earth is as it is. Yet, no fact is better established than the existence of the realities that we interpret as molecules. Their relative weights and other properties have been securely determined. The existence of such a particle is as certain as is the existence of the sun in the high heavens. [Sidenote: Science teaches the composition of the directly unknowable molecules.]