Edison's original street lights were series-wired (remember - he did everything with direct current). To get around the problem with burned-out bulbs, he had two electrodes in the bulb, in parallel with the filament, held apart with a piece of paper. When the bulb burned out, there was enough voltage across the paper to arc through it and burn it away. The two electrodes would then contact and spotweld.
They do the same with Christmas bulbs now days except they use a thin wrap of (specially) insulated wire across the filament supports.
/mike
