79 2 THE POPULAR SCIENCE MONTHLY. 



a tap very like those used on gas-brackets. The stronger the cur- 

 rent 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 air- 

 tight, 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 dis- 

 tinctly 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 elec- 

 tricity 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 in- 

 stantly 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 cir- 

 cuit, which is readily fusible, so that if the current becomes unneces- 

 sarily powerful, it passes through the lead Avire, 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 insert- 

 ing in the circuit a certain amount of resistance, I am able so to re- 

 duce the current flowing from the machine that a considerable lower- 

 ing 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 elec- 



