266 



COMMUNICATION 



elaborate systems of signal communication, which 

 are used chiefly in times of war. By these methods 

 messages are sent in code. 



REFERENCES FOR FURTHER STUDY 

 Texts 



Caldwell and Curtis, Science for Today, Unit 9 



Clement, Collister, and Thurston, Our Surroundings, Chap. 17 



(part) 

 Hunter and Whitman, Science in Our World of Progress, 



Unit 10 

 Lake, Harley, and Welton, Exploring the World of Science, 



Chap. 25 

 Pieper and Beauchamp, Everyday Problems in Science, Unit 



16 

 Van Buskirk and Smith, The Science of Everyday Life, 



Chap. 18 



Webb and Beauchamp, Science by Observation and Experi- 

 ment, Unit 2 

 Wood and Carpenter, Our Environment: How We Use and 



Control It, Topic 12 



Special references 



Beeby, How the World Grows Smaller 

 Earle, Stage Coach and Tavern Days 

 Nida, Following the Frontier 

 Marshall, The Story of Human Progress 

 Fairbanks, The Western United States 



WHAT YOU SHOULD AIM TO ACQUIRE FROM 

 THIS STUDY 



1. What some of the ancient forms of communication 

 were. 



2. How communication developed as civilization ad- 

 vanced. 



TEST OF MASTERY OF THE TOPIC 



In your notebook answer the questions and comply with 

 the instructions. 



1. What people used the heliograph as a means of com- 

 munication? 



2. List some of the forms of communication of the 

 American Indian. 



3. Write a paragraph showing how a great discovery 

 made by Gutenberg influenced the communication of the 

 Middle Ages and after. 



4. Make a list of all the ancient forms of communication 

 which you have discovered and give the name of the people 

 or country responsible for the development of each, in so 

 far as you are able. 



5. When, in your judgment, did the era of modern com- 

 munication begin? 



6. List the discoveries which led to the era of modern 

 communication. 



7. List as many devices as you can which are used to- 

 day for communication. 



8. Cite some incident from your own experience in 

 which you would have been greatly handicapped or en- 

 dangered had you been living in the Middle Ages and had 

 not had the convenience of modern methods of communi- 

 cation. 



9. List as many ways as you can in which modern 

 methods of communication have changed our ways of liv- 

 ing. 



10. Can you suggest some of the problems that have 

 been created as a result of modern communication? 



TOPIC 2. COMMUNICATION BY TELEGRAPH 



SUGGESTED PROBLEMS AND QUESTIONS 



1. What is the early history of the telegraph? 



2. What are the parts of a simple telegraph sys- 

 tem and how are these parts connected into 

 a telegraph circuit? 



3. How are messages sent long distances on land 

 and under sea by telegraph? 



SUGGESTIONS AND HELPS FOR STUDY 



1. Become thoroughly familiar with the problems 

 stated before you attempt their solution. 



2. Be sure to understand the construction of the 

 telegraph key, sounder, and relay. 



3. Get all the experience you can in connecting the 

 various instruments, as this will greatly aid your un- 

 derstanding of the topic. 



4. You can pass Boy and Girl Scout tests by know- 

 ing the Morse code. It can be easily learned by means 

 of the telegraph. 



EXPERIMENTS OR DEMONSTRATIONS WHICH WILL 

 HELP ANSWER THE PROBLEM QUESTIONS 1 



Experiment 162. How do the telegraph key and 

 sounder work? 



If telegraph instruments are not available for this ex- 

 periment, they can be very simply made like those shown 

 in Figure 427. The key is made from two strips of copper 

 and a spool which has been cut in two pieces, one for the 

 key-bar and the other for the switch. The sounder is made 

 from a cigar box, screw eyes, and bolts. The electromagnet 

 is made by winding several hundred turns of wire on the 

 bolt, which is fastened in an upright position. 



Connect the instrument as shown in the illustration with 

 one or two dry cells. Study the set-up carefully and send 

 dots and dashes by means of the key. Trace the current 

 through the instruments. Close the switch on the key and 

 note what happens. 



In your notebook record notes of the experiment and 

 complete the following statements. 



The key is a device used to and the circuit. 



When the key is down, flows in the circuit, magnetiz- 

 ing the of the sounder and causing it to pull the 



bolt up, making a The bar of the sounder drops 



back when the is opened, and the loses its . 



1 See workbook, p. 96. 



