Page:Modern Views on Matter.djvu/14

 6 one hundred-thousandth of an atom's dimension in diameter, it would thereby possess a mass about one-thousandth of that of the lightest atom known, viz. the hydrogen atom.

Such a hypothetical concentrated unit of electricity, especially if it can exist without a material nucleus, it has become customary to call an 'electron,' a name invented by Dr. Johnstone Stoney to designate the so to speak 'atom' or smallest known unit of electric charge. Every electric charge is to be thought of as due to the possession of a number of electrons, but a fraction of an electron is at present considered impossible, meaning that no indication of any further subdivision has ever loomed even indistinctly above the horizon of practical or theoretical possibility.

The electrification of an atom of matter consists in attaching such an electron to it, or in detaching one from it. An atom of matter possessing an electron in. excess is called an 'ion'; and there is reason to know that, considered as a charged body, its charge is that which we have been historically accustomed to designate 'negative'; whereas an atom of matter with one electron in defect is that which has historically been called a 'positive' ion.

This inversion in the natural use of the names positive and negative is inconvenient but accidental and not really serious; it dates from the time of Benjamin Franklin.

These ions or travelling particles of matter have been long known. A liquid or a gas conducts because of the locomotion of its charged particles. The particles travel in an electric field because of their attached charges, all