Arc Electric

Arc, Electric, obtained by sending a sufficiently strong electric current from one carbon pencil to another. To start the action, as the extremely high resistance of the air space between the points would prevent the passage of the current, the carbon points must be made to touch and then be gradually drawn apart. A little of the carbon is volatilised, and so forms a conducting medium between the poles. Its electrical resistance is so considerable, however, that the temperature becomes very high, the carbon poles are rendered white hot, and an intensely brilliant light is emitted. Gold and platinum are readily vaporised, and diamond converted into black amorphous carbon, by the great heat of the arc. In arc lamps there are mechanical or other arrangements for regulating the distance between the two carbons, so that the light may not fluctuate as the pencils are burnt away.