298 



SCIENCE OF HOME AND COMMUNITY 



In order to supply air for the passengers, tanks of com- 

 pressed air are carried. In submarines used for war pur- 

 poses compressed air is also used 

 to work machines to discharge 

 torpedoes. These are arranged 

 so that they can be discharged at 

 an enemy's ship a long distance 

 away. 



Periscope. To enable the peo- 

 ple in a submarine to see the 

 surroundings on the surface of 

 the water, ~a periscope is used. 

 This consists of a long tube reach- 

 ing to the surface of the water 

 and containing mirrors so ar- 

 ranged that one looking through 

 a telescope in the boat is able to 

 see what is in front of the peri- 

 scope. It can be turned so as to 

 face any part of the horizon. 



SUPPLEMENTARY QUESTIONS FOR 

 CLASS DISCUSSION 



Courtesy of Harper 6* Brothers 

 FIG. 1 19. Periscope of submarine. 



I. Summarize briefly the changes 

 that have taken place in the steam- 

 boat during the last hundred years. 



2. What conveniences are found on a modern trans- Atlantic 

 steamship ? 



3. How does the steam turbine differ from the ordinary 

 steam engine used on the locomotive ? 



4. Why is the gyro-compass taking the place of the ordinary 

 compass as a means of guiding ships ? 



5. What provisions have steamships as a protection against 

 accidents ? 



6. What uses can be made of the submarine boat in times of 

 peace ? 



