Page:Incandescent electric lighting- A practical description of the Edison system.djvu/44

 this latter wire and the button of the socket can be either made or broken, thus enabling the lamp to be turned on and off at will.

If the electric current can be forced through a substance that is a poor conductor, it will create a degree of heat in that substance, which will be greater or less according to the quantity of electricity forced through it.

Upon this principle of the heating effect of the electric current, is based the operation of the incandescent lamp just described. While the copper and platinum wires readily conduct the current, the carbon filament offers a great deal of resistance to its passage, and for this reason becomes very hot, in fact is raised to white heat or incandescence, which gives its name to the lamp. You doubtless wonder why this thread of charcoal is not immediately consumed when in this state, but this is readily accounted for when you remember, that without the oxygen of the air, there can be no combustion, and that every possible trace of