90 INTRODUCTION TO GENERAL SCIENCE 



Experiment 29. .The Electric Bell, Telegraph, and Tele- 

 phone. 



Apparatus : Galvanometer which was made in Experiment 

 28, large nail, smaller nail, fifty feet No. 20 insulated copper 

 wire, dry cell, steel magnet and coil which was made in Ex- 

 periment 28. 



a. Wind nearly all of the wire upon the large nail in smooth 

 layers; fasten one end of the wire to the small nail, taking 

 care that the bare copper comes into contact with it ; fasten the 

 other end to one of the dry cell terminals, and connect a wire to 

 the other terminal of the dry cell. When this wire is touched 

 to the small nail, it is attracted to the large nail. If care is used, 

 the small nail may be made to vibrate very rapidly. When a 

 single tap is made by the small nail, the telegraph is illustrated; 

 if the small nail vibrates, we have a simple electric buzzer, 

 which would ring a bell if the latter were properly placed. 



6. Attach the ends of the coil, in which the steel magnet 

 lies, to the galvanometer, with wires which are at least six 

 feet long. Bring a piece of iron (the nail) up to the magnet, 

 and note the deflection. Pull the iron away and note the de- 

 flection. The motions must be rapid. What do you con- 

 clude? This illustrates the simple telephone. When the 

 voice strikes the iron plate of a receiver used as a transmitter, 

 it is made to vibrate, and currents are caused to flow in the 

 wire around the magnet in the back of the iron plate. These 

 currents affect a similar plate in the other receiver, and it 

 makes the same movements as does the first iron plate. 



66. CHEMICAL EFFECTS OF ELECTRICITY 

 Electricity, when passing through a chemical solution, 

 tends to separate the chemicals into their components. Thus 

 water is separated into two volumes of hydrogen and one 



