Amber; also, the alloy of gold and silver, called electrum.
One of those particles, having about one thousandth the mass of a hydrogen atom, which are projected from the cathode of a vacuum tube as the cathode rays and from radioactive substances as the beta rays; -- called also corpuscle. The electron carries (or is) a natural unit of negative electricity, equal to 3.4 x 10-10 electrostatic units. It has been detected only when in rapid motion; its mass, which is electromagnetic, is practically constant at the lesser speeds, but increases as the velocity approaches that of light. Electrons are all of one kind, so far as known, and probably are the ultimate constituents of all atoms. An atom from which an electron has been detached has a positive charge and is called a coelectron.