676 THE POPULAR SCIENCE MONTHLY. 



I can raise the poker from its position without difficulty ; but, now I 

 join on the wires connected with the battery to the coil of the electro- 

 magnet, the poker is attracted with greater force than my strength 

 can overcome. The effect is more perceptible by the use of nails 

 instead of the poker. When the current is on you see that, owing to 

 the attraction of the nails by the magnet, I am able to build up an 

 ornamental triumphal arch of nails, but, directly I take off the current, 

 the magnetism ceases, and the nails succumb to the force of gravity, 

 and fall to the floor. I have here the parts of an electro-magnet dis- 

 jointed, which I will put together to illustrate the utility of this power 

 of attraction. I place the iron bar surrounded with wire on the table, 

 and, on holding nails to it, you see it possesses no attractive power. 

 If I let the current pass from the battery through the coil, the iron is 

 magnetized, the attractive action is immediately set up, and the nails 

 are attracted. Now, suppose I want to utilize this power to ring this 

 bell the dome which I struck a short time ago I place the hammer 

 (which is attached to a piece of iron in position to be attracted similar 

 to the nails, so as to imitate the motion of my wrist) in front of the 

 electro-magnet ; I then place the bell-dome on its rod, so that the 

 hammer, when drawn forward, will fall upon it ; and, as you will see, 

 the arrangement is complete in that simple form, for each time a cur- 

 rent is sent the iron armature is attracted by the magnet bringing 

 with it the hammer which strikes the bell by its forward motion. 

 This is the principle on which all electric bells are constructed. A 

 similar arrangement is employed for giving alarms in case of burglary. 

 A small switch arrangement is attached to the frame-work of the bed- 

 room-door [a small door so fitted was exhibited] ; this switch is put 

 on on going to bed, and, should the door be opened by any one during 

 the night, a succession of currents of electricity are sent to a bell, 

 which continues to ring till attended to, and it would be a bold burg- 

 lar who dared to carry on his nefarious business under such a din. A 

 modification of this arrangement can be adapted to innumerable pur- 

 poses. In America, where servants are not so plentiful as in England, 

 necessity has compelled the employment of electricity for domestic 

 purposes, to a far greater extent than in England. In nearly every 

 town in America, sj^stems of wires extend to almost every house, in 

 the hall of which is a small instrument [one was exhibited], on the 

 dial of which divisions bear the various words messenger, carriage, 

 coupe, express-wagon, doctor, police, fire, and two or three other 

 things, and on turning the instrument pointer to any division, and 

 drawing down a spring, a call is sent to the central office or bureau, 

 and the instrument there indicates the service required and at what 

 house, and the request is carried out at once. While traveling in 

 America, I was once afraid that I should not have time to reach the 

 nearest telegraph -office, to dispatch a telegram in reference to an 

 appointment ; and, on mentioning my concern to the lady in whose 



