290 



COMMUNICATION 



tially serving to change the waves into current 



waves. 



12. Make a diagram showing the parts of the three- 

 element vacuum tube. 



13. Explain in detail how the tube acts as a detector. 



14. The of the vacuum tube acts as a valve control- 

 ling the flow of electrons from the to the 



15. The currents set up in the aerial of a receiving set 

 are of very high . 



16. These currents are amplified by __ and by . 



17. The loud speaker is essentially a 



18. Vibrations between _ _ and 



are called radio 



frequency because they are above the range of the 

 19. The "A" battery is used to 



20. Vacuum tubes are used not only in radio communica- 

 tion but also in 



21. Some radio sets are called "5-tube sets." These gen- 

 erally have one tube for a detector, two for radio fre- 

 quency amplification, and two for audio frequency am- 

 plification. Explain what is meant by the last two state- 

 ments. 



22. What does the rheostat in the filament circuit do? 



23. and are used to tune radio sets. 



24. Sound for moving pictures may be recorded either 

 on a or on 



25. A photo-electric cell changes energy to 



energy. 



26. When scenes are sent by wire or wireless the process 

 is called . 



SUPPLEMENTARY MATERIALS 



Reading suggestions 



Hogan, The Outline of Radio (Little) 



Collins, The Radio Amateur's Hand Book (Crowell) 



Burns, The Story of Great Inventions (Harper) 



Bond, The American Boys' Engineering Book (Lip- 

 pincott) 



Caldwell and Slosson, Science Remaking the World 

 (Doubleday) 



Elliot, The Romance of Savage Life (Lippincott) 



Gibson, The Romance of Modern Electricity (Lippin- 

 cott) 



Holland, Historic Inventions (MacRae Smith) 



Darrow, Masters of Science and Invention (Har- 

 court) 



lies, Leading American Inventors (Holt) 



Marshall, The Story of Human Progress (Macmillan) 



Johnson, Modern Inventions (Nelson) 



Baker, The Boy's Second Book of Inventions (Double- 

 day) 



Williams, The Romance of Modern Invention (Lip- 

 pincott) 



Yates, ABC of Television (Henley) 



Woodbury, Communication (Dodd) 



Reports which may be prepared 



1. Communication by the heliograph 



2. Laying an ocean cable 



3. What happens at the telephone exchange 



4. Early telephones 



5. Modern devices in the telegraph office 



6. The workings of the dial phone 



7. Submarine signaling during the war 



8. An electron goes through the radio set 



9. Picture writing of the ancients 



10. The making of a modern newspaper 



11. Edison's contributions to telegraphy 



12. The workings of the U. S. Mail 



13. The screen grid radio tube 



14. The future of television 



15. The possibilities of sending pictures by wire- 

 less 



Great scientists you should know about 



1. Samuel F. B. Morse 



2. Alexander Graham Bell 



3. Guglielmo Marconi 



4. Lee DeForest 



Investigations and things to do 



1. Build a telegraph key and sounder. 



2. Build a telephone transmitter. 



3. Build a telephone receiver. 



4. Build a wireless sending set. 



5. Build a crystal receiving set. 



6. Build a tube radio set. 



