Things Electricity Can Do.--Exp. 191, To study the action of a simple telegraph sounder.--Discussion.--Telegraph Line; Connections.--Operation of Line.--Exp. 192, To study the action of the "relay" on telegraph lines.--The Relay.--Exp. 193, To study the action of a two-pole telegraph instrument.--Exp. 194, To study the action of a simple "single needle telegraph instrument."--Exp. 195, To study the action of a simple automatic contact breaker, or current interrupter.--Automatic Current Interrupters.--Exp. 196, To study the action of a simple electric bell, or a "buzzer."--Electric Bells and Buzzers.--Exp. 197, To study the action of a simple telegraph "recorder."--Exp. 198, To study the action of a simple "annunciator."--Discussion.--Exp. 199, To study the shocking effects of the "extra current." Induction Coils.--Action of Induction Coils.--Transformers.--The Dynamo.--The Electric Motor.--Exp. 200, To study the action of the telephone.--The Telephone.--The Bell, or Magneto-transmitter.--The Receiver.--The Carbon Transmitter.--Induction Coils in Telephone Work.--Electric Lighting and Heating.--Arc Lamps.--The Incandescent Lamp. CHAPTER XXVIII. WIRE TABLES 208 APPARATUS LIST 210 INDEX 215 MAGNETISM A Few Dont's for Young Students. Don't fail to make at least a part of your own apparatus; there is a great deal of satisfaction and pleasure in home-made apparatus. Don't experiment in all parts of the house, if working at home. Fit up a small room for your den, and carry the key. Don't begin an experiment before you really know what you are trying to do. Read the directions carefully, then begin. Don't rush through an experiment to see what happens at the end of it. See what happens at each step, and notice every little thing that seems unusual. Don't try to do all parts of an experiment at the same time. Understand one part, then proceed. Don't fail to ask yourself questions, and form an opinion about the results of an experiment before you read what the author has to say about it. Don't fail to keep a note-book. Keep all the data and arithmetical work for future reference. Don't leave the apparatus around after you have finished the day's work. PART I.--MAGNETISM. CHAPTER I. IRON AND STEEL. _=1. Introduction.=_ We should know something about iron and steel at the start, because we are to use them in nearly every experiment. The success with some of the experiments will depend largely upon the quality of the iron and steel used.