It took many years of patient research to arrive at definite conclusions; in fact, it may be said that definite conclusions have not even yet been reached,--though more or less unanimity of opinion exists as to the structure of atoms. The new theory of matter is that each atom is built up of negative “electrons,” and positive “protons”--the former revolving round the latter in orbits analogous to those of our solar system. The protons, positively charged, remain in the center of the atom; the electrons, negatively charged, circle about them, just as our planets circle about the sun. The number of these protons and electrons varies according to the nature of the element. Hydrogen representing unity, has but one electron revolving around a single proton; helium comes next, with two; and so on, up the scale, until we reach uranium, which has ninety-two. The positive and the negative charges balance one another in all stable atoms; and when this is not the case, the atom tends to go to pieces or disintegrate; electrons are shot off, which join some other atom, and radio-activity results. The nature of the element itself is accordingly changed, and may even be so fundamentally changed by this process that it turns into something else; _i. e._, the transmutation of one element into another has taken place, as dreamed of by the alchemists! Hence we often hear of the “new alchemy.” This, in rough outline, is the modern conception of the atom, and of the constitution of matter generally. WITHIN THE ATOM Let us now endeavor to analyze the atom more closely, in the light of these newer researches. We have seen that the electrons revolve round the central protons. These protons are probably composed of electrons and hydrogen nuclei. The total central “sun”--to use the astronomical analogy--is known as the nucleus. The relative sizes of these bodies may be appreciated when it is stated that they have been compared to the sizes of the planets, relative to the distances separating them from the sun. Vast spaces exist, therefore, within the atom, in which the electrons revolve. Yet the atoms themselves are inconceivably small! The following quotation from Bertrand Russell’s “A. B. C. of Atoms” will perhaps make this clear. He says: