The great importance of this invention can be better understood and appreciated by a brief glance at the state of the art in 1878-79, when Edison was conducting the final series of investigations which culminated in his invention of the incandescent lamp and SYSTEM of lighting. At this time, and for some years previously, the scientific world had been working on the "subdivision of the electric light," as it was then termed. Some leading authorities pronounced it absolutely impossible of achievement on any extended scale, while a very few others, of more optimistic mind, could see no gleam of light through the darkness, but confidently hoped for future developments by such workers as Edison.

The earlier investigators, including those up to the period above named, thought of the problem as involving the subdivision of a FIXED UNIT of current, which, being sufficient to cause illumination by one large lamp, might be divided into a number of small units whose aggregate light would equal the candle-power of this large lamp. It was found, however, in their experiments that the contrary effect was produced, for with every additional lamp introduced in the circuit the total candle-power decreased instead of increasing. If they were placed in series the light varied inversely as the SQUARE of the number of lamps in circuit; while if they were inserted in multiple arc, the light diminished as the CUBE of the number in circuit.[29] The idea of maintaining a constant potential and of PROPORTIONING THE CURRENT to the number of lamps in circuit did not occur to most of these early investigators as a feasible method of overcoming the supposed difficulty.