THE SMALLEST WORKERS 



cells, is made to encounter a relatively resistant medium 

 in the course of its flow along the conducting circuit. 

 Such resistance leads to the production of active vi- 

 brations among the particles of the resisting medium, 

 producing the phenomena of heat and, if the activity 

 is sufficient, the phenomena of light also. It will thus 

 appear that in this class of cases, as in the other, there 

 is an actual re-transformation of electrical energy into 

 the energy of motion, only in this case the motion is 

 that of molecules and not of larger bodies. The prin- 

 ciple is utilized in the electrical heater, with which our 

 electric street-cars are commonly provided, and which is 

 making its way in the household for purposes of general 

 heating and of cooking. It is utilized also in various 

 factories, where the very high degree of heat attainable 

 with the electrical furnace is employed to produce chem- 

 ical dissociation and facilitate chemical combinations. 

 By this means, for example, a compound of carbon and 

 silicon, which is said to be the hardest known substance, 

 except the diamond, is produced in commercial quanti- 

 ties. A familiar household illustration of the use of 

 this principle is furnished by the electric light. The car- 

 bon filament in the electric bulb furnishes such resist- 

 ance to the electric current that its particles are set vio- 

 lently aquiver. Under ordinary conditions the oxygen 

 of the air would immediately unite with the carbon 

 particles, volatilizing them, and thus instantly destroy- 

 ing the filament ; but the vacuum bulb excludes the air, 

 and thus gives relative permanency to the fragile thread. 

 The third class of cases in which the electric current 

 is commercially utilized is that in which the transforma- 



