For one thing, they may become valuable adjuncts to the older form of iron and steel furnaces, from which they will obtain their power free, gratis and for nothing. In districts such as Middlesbrough they could generate more electricity than they have any use for. The ordinary iron furnaces belch forth flames which are really good useful gas (carbon monoxide) burning to waste. Many of the furnaces are covered in at the top, and this gas is led away to heat boilers for the steam-engines or to drive large gas-engines, but in a large works there is more of this waste gas than they know what to do with. Now that could, and probably will ere long, be turned into electricity by means of gas-engines and the current used for making steel in induction furnaces. It will probably surprise many to know that these enormous currents which can thus heat great masses of metal until they melt are no danger at all to the men who work with them. A man might dip an iron rod into the trough of metal and he would scarcely feel the shock. And the same is true of the welding machine, which can be touched in any part without fear. The reason, of course, is that, broadly speaking, it is volume of current which does harm, and the resistance of the human body is so great that with the small voltages used, the volume which can pass is negligible. It should be mentioned, however, that the volume of current in lightning is also small, but we know that it is capable of inflicting terrible injury. Lightning, however, is in a class by itself. Our terrestrial voltages are baffled by an air-gap of a few inches, but lightning springs across a gap miles wide. Its voltage must, therefore, amount to millions, and the ordinary rules relating to earthly currents do not apply. But other sources of heat besides electricity are at the disposal of our manufacturers nowadays. Pre-eminently there is the flame of some gas burning with pure oxygen. The oxyhydrogen jet has been known for many years as the best means of producing the light for a magic lantern. Such a jet impinging upon a pencil of lime causes the latter to glow with a dazzling white light.