Note: Do not rely on this information. It is very old.
Jablochkoff's CandleJablochkoff's Candle, now practically obsolete, was an electric arc-lamp composed of two parallel rods of carbon placed side by side, separated by a thin layer of kaolin or Chinese clay. A rapidly alternating current was sent up one rod, and passed across the top down the other rod. An arc light was thus produced, and the two rods were consumed at the same rate by reason of the alternations. The heat developed was sufficient to burn away the clay at the arc.