The quadruplex has not as a rule the same working efficiency that four separate wires have. This is due to the fact that when one of the receiving operators is compelled to "break" the sending operator for any reason, the "break" causes the interruption of the work of eight operators, instead of two, as would be the case on a single wire. The working efficiency of the quadruplex, therefore, with the apparatus in good working condition, depends entirely upon the skill of the operators employed to operate it. But this does not reflect upon or diminish the ingenuity required for its invention. Speaking of the problem involved, Edison said some years later to Mr. Upton, his mathematical assistant, that "he always considered he was only working from one room to another. Thus he was not confused by the amount of wire and the thought of distance." The immense difficulties of reducing such a system to practice may be readily conceived, especially when it is remembered that the "line" itself, running across hundreds of miles of country, is subject to all manner of atmospheric conditions, and varies from moment to moment in its ability to carry current, and also when it is borne in mind that the quadruplex requires at each end of the line a so-called "artificial line," which must have the exact resistance of the working line and must be varied with the variations in resistance of the working line. At this juncture other schemes were fermenting in his brain; but the quadruplex engrossed him. "This problem was of most difficult and complicated kind, and I bent all my energies toward its solution. It required a peculiar effort of the mind, such as the imagining of eight different things moving simultaneously on a mental plane, without anything to demonstrate their efficiency." It is perhaps hardly to be wondered at that when notified he would have to pay 12 1/2 per cent. extra if his taxes in Newark were not at once paid, he actually forgot his own name when asked for it suddenly at the City Hall, lost his place in the line, and, the fatal hour striking, had to pay the surcharge after all!