molecules, of dimensions similar to those almost simultaneously discovered by Thomson. Later developments of optical theory stimulated by this discovery indicated the presence in molecules of positively charged particles as well, but that these were atomic in size.
Thus three independent lines of investigation have almost simultaneously converged to furnish a basis for a new theory of electricity, which we need follow only so far as it affects the theory of matter. Of the two kinds of electricity we find but one—the negative—that can be detached from atoms. We find the negative electron too as a constituent of the atom. The electron, whatever its source, is always the same, while the positive charge partakes of the varying nature of the matter with which it is associated. Emphasis is thus laid upon the electrons as forming the true electrical fluid, the positive electricity playing a subordinate part. According to this theory a neutral atom, which we know contains some electrons, contains also enough positive charge to exactly neutralize them. If one or more additional electrons become attached to it, it becomes negatively charged with the atomic quantity or its multiple. If, on the other hand, it loses some of its electrons, it becomes positively charged. The terms positive and negative have here exchanged their usual roles. It is the positive electricity that is
der Geist der stets verneint,
"the spirit of negation." Except for this exchange (due to the unfortunate original allotment of the terms) the theory bears a remarkable resemblance to the single fluid theory of Franklin.
Some atoms normally contain too many electrons, others too few. These will attract each other, forming neutral molecules. Thus an oxygen atom, which normally holds two extra electrons, will attract to itself two hydrogen atoms which each lack one, and thus will form a molecule of water. By the number of electrons in excess or deficiency the combining power of an atom with others is determined. Such considerations have proved efficient in disentangling many puzzling questions connected with chemical combination.
The most salient point of this theory is that we seem to be confronted with a dualism, matter and electricity, atoms and electrons. A closer study of the electron has suggested a possible way of escaping this, or rather of turning it, in what is called the electrical theory of matter.
Long before electrons were observed J. J. Thomson had shown theoretically that a body when charged with electricity would by mechanical tests appear to have a slightly greater mass than when uncharged, and the smaller the body the greater the effect. Thus it would require more work to stop a moving charged body than if it were uncharged; a greater force would be needed to deflect it from its path. But even an
