Page:Popular Science Monthly Volume 49.djvu/237

ters, and deck planers are designed in forms which combine motor and tool; so much is thereby gained in adaptability that a remodeling is in progress of much light machinery in its first estate rigidly limited in play by shafts, belts, or gearing. Dentistry and other arts of refined manipulation are indebted for novel facilities to the flexible mechanical shaft—a tightly wound coil of steel wire. This device is in turn being shown to the door by the new partnership between an electric thread and a tool. And the wire, however slender, which binds a reservoir of power to its work, can on occasion be discarded, as in the rolling contact of the electric trolley wheel. And even contact can be dispensed with if strict economy is not imperative. We are familiar with the annoyance, due to induction, of being obliged in a telephone circuit to overhear other subscribers, whose wires are often far distant from our own. A hint in this for the engineer at the head of the British telegraphs, Mr. Preece. Utilizing induction, he has established a telegraph between Oban and Auchnacraig, divided by six miles of sea, using wires strung along the opposite shores. Electricity, light, heat, and chemical action are all in essence motion; electricity is the most desirable of them all, because it can most readily and fully become the source or issue of any other. The pre-eminent sensitiveness of electrical apparatus makes it a surpassing means of measuring minute portions of space or time, of light, heat, chemical activity, or mechanical motion. Hence a brood of telltales of widely contrasted purpose. Selenium, a metalloid of the same lineage as sulphur, and betraying its descent by a striking family resemblance, has the curious property of transmitting electricity more freely in light than in darkness; a stick of selenium, therefore, is the pivot of a device to give warning when extinction befalls a lamp charged with important duty. In thermometers a circuit broken or completed acts as a fire signal, or, on shipboard, heralds the approach of an iceberg. Electric fingers sound a gong when the water recedes below the safety level in a steam boiler, or report an attempted breach of bolt or bar by the burglar's jimmy. Each of these warnings can be registered at a distance, so that in case of neglect by an attendant there can be no disputing the fact. Now, if an electric alarm can summon a servant to duty, why may not the inventor go further, and so add to his device that it shall of its own motion do what needs to be done? Accordingly, we find furnaces fitted up with electrical control, so that the draft is opened or fuel added when the temperature falls too low, or the reverse, when the flame is too fierce; when the fuel is gas this stoking leaves nothing to be desired. New mechanism of this kind is constantly being contrived. The inventor who began by conferring electric nerves on muscles of brass and iron has.