WHY PROGRESS IS BY LEAPS. 223 



ters^ and 'deck planers are designed in forms which combine motor 

 and tool ; so much is thereby gained in adaptability that a re- 

 modeling 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 pur- 

 pose. Selenium, a metalloid of the same lineage as sulphur, and 

 betrajdng 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 com- 

 pleted acts as a fire signal, or, on shipboard, heralds the ap- 

 proach 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. ISTew mechanism of this 

 kind is constantly being contrived. The inventor who began by 

 conferring electric nerves on muscles of brass and iron has. 



