Yablochkov candle
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A Yablochkov candle (sometimes electric candle) is a type of electric carbon arc lamp, invented in 1876 by Pavel Yablochkov.
It consisted of a sandwich of two long carbon blocks, approximately 6 by 12 millimetres in cross-section, separated by a block of inert material such as plaster of paris or kaolin. There was a small piece of fuse wire or carbon paste linking the two carbon blocks at the top end. The assembly was mounted vertically into a suitable insulated holder.
On application of the electric supply, the fuse wire 'blew' and struck the arc. The arc would then continue to burn, gradually consuming the carbon electrodes (and the intervening plaster) as it did so. The first candles were powered by an alternating current Gramme machine.
On disconnecting the supply, the arc would extinguish. It could not be restarted as there was now no circuit between the electrodes. It was necessary to replace the candle with a new one.
The advantage of the design was that it removed the need for any mechanical apparatus, a regulator, to maintain the needed distance between the carbon blocks to sustain the arc.
It was first demonstrated, as street and theatre illumination, during the Paris Exhibition of 1878, notably on the Avenue de l'Opéra. The candles were enclosed in globes of enamelled glass, with four to twelve candles in each connected in series.