ELECTRICITY. 387 



by the issuing of a current of electricity from tlie point, -will bo sufficient to 

 deflect the flame, and even blow it out. 



Howdoeseiec "^^7. The passage of electricity from one 

 hi^t? ^^°''* substance to another is generally attended with 

 an evolution of heat, and a current of electricity 

 passing over an imperfect conductor, raises its temperature. 

 The temperature of a good conductor of sufficient size 

 to allow the electric fluid to pass freely, is not affected by 

 the transmission of a current of electricity ; but if its size 

 is disproportionate to the quantity of fluid passing over 

 it, it will be heated to a greater or less degree. ^ 



If a small charge of electricity be passed through small metal wire a few 

 inches in length, its temperature will bo sensibly elevated ; if the charge be 

 increased, the wire may be made red hot, and even melted and vaporized. 



The worst conductors of electricity suffer much greater changes of tem- 

 perature by the same charge than the best conductors. The charge of elec- 

 tricity which only elevates the temperature of oue conductor, will sometimes 

 render another red hot, and will volatiUze a third. 



The heat developed in the passage of electricity through 

 combustible or explosive substances, which are imperfect 

 conductors, causes their combustion or explosion. 



If gunpowder be scattered over dry cotton loosely wrapped round ono end 

 of a discharging-rod, it may be ignited by the discharge of a Leyden jar. 



In the same way powdered resin may be inflamed. 



Ether or alcohol may be also fired by passing through it an electric dis- 

 charge. Let cold water be poured into a wine-glass, and let a thin stratum 

 of ether be carefully poiired upon it. The ether being lighter will float on 

 the water. Let a wire or chain connected with the prime conductor of a 

 machine be immersed in the water, and, while the machine is in action, pre- 

 sent a metallic ball to the surface of the ether. The electric charge wiU pass 

 from the water through the ether to the ball, and will ignite the ether. 



If a person standing on an insulated stool touches the prime conductor 

 "with one hand, and with the other transmits a spark to the orifice of a gas- 

 pipe from which a current of gas is escaping, the gas will be ignited. 



By the friction of the feet upon a dry woolen carpet, sufiBcient electricity 

 may be often excited in the human body to transmit a spark to a gas-burner, 

 and thus ignite the gas. 



If we bring a candle wirh a long snufl) that has just been extinguished, 

 near to a prime conductor, so that the spark passes from the conductor, 

 through the smoke, to the caudle, it may be relighted. 



Is the electric Thc clcctric fluid is not itself luminous ; but 

 fluidiumiaouB? -^.g Q^Q^jon ovcr impcrfcct conductors, or from 



