There are ten furnaces in all, built loosely of fire-brick, and fitted at each end with electrical connections. And strange they look to one who is familiar with the ordinary fuel furnace, for they have no chimneys, no doors, no drafts, no ash-pits, no blinding glow of heat and light. The room in which they stand is comfortably cool. Each time a furnace is charged it is built up anew; for the heat produced is so fierce that it frequently melts the bricks together, and new ones must be supplied. There were furnaces in many stages of development. One had been in full blast for nearly thirty hours, and a weird sight it was. The top gave one the instant impression of the seamy side of a volcano. The heaped coke was cracked in every direction, and from out of the crevices and depressions and from between the joints of the loosely built brick walls gushed flames of pale green and blue, rising upward, and burning now high, now low, but without noise beyond a certain low humming. Within the furnace--which was oblong in shape, about the height of a man, and sixteen feet long by six wide--there was a channel, or core, of white-hot carbon in a nearly vaporised state. It represented graphically in its seething activity what the burning surface of the sun might be--and it was almost as hot. Yet the heat was scarcely manifest a dozen feet from the furnace, and but for the blue flames rising from the cracks in the envelope, or wall, one might have laid his hand almost anywhere on the bricks without danger of burning it. [Illustration: Taking Off a Crust of the Furnace at Night. _The light is so intense that you cannot look at it without hurting the eyes._] In the best modern blast-furnaces, in which the coal is supplied with special artificial draft to make it burn the more fiercely, the heat may reach 3,000 degrees Fahrenheit. This is less than half of that produced in the electrical furnace. In porcelain kilns, the potters, after hours of firing, have been able to produce a cumulative temperature of as much as 3,300 degrees Fahrenheit; and this, with the oxy-hydrogen flame (in which hydrogen gas is spurred to greater heat by an excess of oxygen), is the very extreme of heat obtainable by any artificial means except by the electrical furnace. Thus the electrical furnace has fully doubled the practical possibilities in the artificial production of heat.