Page:Popular Science Monthly Volume 20.djvu/814

792 a tap very like those used on gas-brackets. The stronger the current supplied to the lamp, the greater its heat and brilliancy; and when, by turning a handle in the instrument I have for the purpose, the strength of the current is increased, it forms a brilliant light in the glass tube, until the amount of current is greater than the carbon can stand, when it radiates a beautiful blue haze, which indicates that its end is near, and then it is broken (as you see), and the lamp goes out. I can easily replace the broken lamp by unscrewing it out of its socket, and placing a fresh one in its place, when at once all is in good order, and the light resumed. These lamps are water-tight as well as airtight, and to prove this I will insert a lighted lamp into the little aquarium on the table, when you see that the globe is brilliantly lit up, and that the fish it contains show rather a sign of curiosity than discomfiture, and seem rather proud of their colors which are so distinctly brought out by the brilliancy of the light. Here I have a globe of colored water to show what brilliant effects can be produced. A good deal has been said about the dangers of electric lighting, and how careful we ought to be in its use, and there is no doubt that electricity is a very dangerous agent if you do not know how to use it. We have heard of the danger from fire through its use in theatres and houses, but I want to show you that, when I place a cambric pocket handkerchief round a lamp, which I then break while electricity is going through it, no spark or fire of any kind occurs, but the lamp instantly goes out. There is also danger from wires coming in contact with each other, and in that case they short circuit the machine; they cause an increased strength of current to flow, producing heat, and in that manner setting fire to houses. To obviate this danger, "safety-catches" have been introduced by Mr. Edison. These safety-catches consist in the insertion of a very small piece of lead wire in the circuit, which is readily fusible, so that if the current becomes unnecessarily powerful, it passes through the lead wire, heats it to fusing point, and so breaks down the section on which the "safety-catch" is placed, eliminating at once all danger. It does not affect any other lamps, as you see. When the fused safety-catch is replaced by a good one, the lamps which were broken down by its rupture become lighted up again. We have the means of regulating the lights now burning in the room, Here is an apparatus in connection with the machine at the engine-station, and, by moving the handle and inserting in the circuit a certain amount of resistance, I am able so to reduce the current flowing from the machine that a considerable lowering of the light takes place. On turning the handle back again, the former brilliancy returns. That shows the electric light in the latest stage of its perfection. We have a bright light now in this room, but no impure gases are given off by the electric light, and the air is not vitiated by it. The room is warm, but that warmth is due to the number of people present, and not to the heat produced by the