There was one difficulty with the "candle" that seemed insurmountable for a time--the wasting of the two carbons was unequal, as in any arc light, the points thus gradually drawing apart until the passage of the current was no longer possible. To overcome this the rapidly wasting positive carbon was made double the thickness of its mate; but while this answered fairly well the thinner negative carbon gradually became heated by the increased resistance, and burned up too rapidly. The difficulty was finally overcome by the simple expedient of alternating the flow of the current, so that each carbon was alternately a positive and a negative pole. As the magneto-electric machines then in use produced alternating currents it was only necessary to use such machines for generating the current to produce an equal destruction of both carbons. The simplicity and excellence of the light of these "candles" brought them at once into general popularity, not only in the large cities of Europe, but in many out-of-the-way places. Greece, Portugal, and other obscure European countries adopted them, and even Brazil, La Plata, and Mexico installed many plants. But stranger still, they were soon used for illuminating the palaces of the Shah of Persia and the King of Cambodia, and a little later were introduced into the residence of the savage King of Burma. In short, their use became universal almost immediately. THE IMPROVED ARC LIGHT About the time that Jablochkoff's candles were making such a sensation in Europe, Charles F. Brush, of Cleveland, Ohio, invented an arc light in which the carbons were set point to point, the distance being maintained and the necessary feed produced automatically in much the same manner as in the lamps used at present. Other inventions soon followed, some of the lamps being regulated by clockwork, some by electricity and magnetism. The advantage of this type of arc lamp over the candle type--an advantage that led to its general adoption--was largely that of efficiency, a far greater amount of light being obtainable from the same expenditure of power by the point-to-point type of lamp. In this lamp it is necessary that the points of carbon shall come in contact when the current is off, but be drawn apart a moment after the current is turned on, and remain at this fixed distance. To accomplish this, the lower carbon is usually made stationary, the feeding being regulated by the position of the upper carbon. In the usual type of modern lamp the passage of the current causes the points to separate the required distance through the action of an electromagnet the coils of which are traversed by the current. A clutch holds the carbon in place, the position of this being also determined by an electromagnet. The action is regulated by the difference in the resistance to the passage of the current caused by the increase in the separation of the points.