In the above statements regarding the possibility of the transformation of each of the several forms of Substance, into other forms, the reference has been applied only to the three better known forms, _i.e._, Solid, Liquid and Aeriform. The fourth form or state of Substance, known as Radiant Matter, is of too recent discovery to admit of its properties being accurately observed. The best and latest opinion of Science, however, is that it constitutes what may be called "Primal Matter"--that is substance from which all other forms, states, kinds and varieties of Substance arise--the "stuff" from which they are manufactured. Science seems to be discarding the Ether theory of the Origin of Matter, in favor of this "Primal Matter." Physical Science divides Substance into Masses, Molecules, and Atoms--that is, the old Physical Science did, but the later investigators now see that even the Atom may be sub-divided. But the old terms may as well be used, at least for the time being. Let us consider these divisions. _A "Mass"_ is a quantity of Substance considered as a whole--but which is composed of a collection or combination of parts (molecules.) A lump of coal; a piece of iron; a portion of meat, even a drop of water, is a Mass. The only requisite for a Mass, is that it contains two or more parts or molecules. Therefore a Mass is a collection or combination of two or more molecules, considered as a whole. _A "Molecule"_ is the _physical_ unit of Substance, or, in other words, the smallest part of any kind of Substance that can exist by itself and still remain that particular "kind" of substance. (But not the smallest chemical part--the latter is called an Atom, and Atoms combine to form a Molecule.) The Molecule exists as a unit, and cannot be split or separated by physical means, although it may be separated into Atoms by chemical means. In order that we may form a clear idea of the Molecule, let us take a very small Mass of Matter--a drop of water, for instance. This drop of water is a Mass composed of a great number of molecules. It may be divided, and sub-divided, into smaller and still smaller parts. This division may be carried on until it reaches a point where our sight and instruments are unable to make a further sub-division. But, theoretically, the work may be carried on still further, until at last a limit is reached where we are unable to divide the water into any smaller parts, without separating its chemical constituents from each other, in which latter case there would be no water at all, its chemical constituents (or Atoms) having separated and now appearing as two atoms of Hydrogen and one atom of Oxygen, separated and apart and no longer forming a molecule of water.