370 Introduction to the Study of Science 



(6) Show how it operates. 7. (a) Who made the first steam turbine? 

 (&) Describe and explain its operation. 8. Compare the steam tur- 

 bine and the reciprocating engine as to the advantages and disad- 

 vantages for navigation. 9. (a) Mention a modern steamship which 

 is equipped exclusively with steam turbines. (6) One which combines 

 reciprocating and turbine engines. 10. Describe a steam turbine of 

 the Parsons type. 11. In what way does the Curtis turbine resemble 

 the Pelton water wheel? How does it differ from it? 12. Why are 

 steam turbines employed to utilize the energy of the exhaust steam from 

 reciprocating engines ? 13. How does a steamship with turbines pro- 

 vide for reversing? 14. What devices have been made to reverse the 

 direction of the screw propellers without reversing the steam turbines ? 

 15. Explain how the submarine submerges or emerges. 



16. (a) What motive power is used by submarines when at the sur- 

 face? (6) When submerged? (c) What type of engine is employed? 



17. What forces must a submarine withstand? 18. Describe a peri- 

 scope and explain its use. 



19. In what ways has the application of steam power to navigation 

 affected human life? 



VI. INSTRUMENTS OF NAVIGATION 



The routes over which vessels travel are unmarked except 

 on the charts of the ship's officers. To determine the location 

 of the vessel accurately and to steer the course required, it is 

 necessary for the mariner to have certain instruments as well 

 as charts showing sailing routes. The indispensable instru- 

 ments are the compass, the sextant, and the chronometer. 

 To-day a steamer or sailing vessel has also a log, a barometer, 

 and other instruments in its equipment. 



163. Invention of the compass. The invention and use of 

 the compass made possible the ocean voyages of exploration 

 and discovery in the fifteenth and succeeding centuries. When 

 or by whom the compass was invented, or when and how it was 

 introduced into Europe, are not known. Tradition has it that 

 the Chinese more than two thousand years ago discovered the 

 " magnetic needle " and made use of it in traversing the great 

 plateaus of the empire. Certainly the compass was used in 

 travel on land before its use in navigation was discovered. 



