384 FORMS OF FNFRGY v^. What aids does the radio make available to a pilot? 4. Define: (a) compass course, (b) true course, (c) compass heading, and (d) the track. 5. What aids are available for terrestrial navigation? 6. What is a relief map? 7. What is meant by a contour? 8. How are different altitudes shown on a relief map? 9. When in flight how would you check your ground speed over a given course? 10. How would you know whether or not the direction of the wind shifted while in flight? 11. Differentiate between ground speed and airspeed. 12. Compare the relative usefulness of the four types of avigation, indicating the conditions under which each one could be used to best advantage. 13. What aids does the radio make available for avigation? 14. What data are necessary for celestial observation? What are the sources of these data? 15. What information do aeronautical charts contain? 16. How are civil airways marked? 17. Does an air-speed indicator give a true reading at various altitudes? 18. What is a sextant? 19. What is dead reckoning? 20. What is meant by instrument flying?
UNIT VI ENERGY MAY BE PROPAGATED THROUGH THE ETHER AND THROUGH MATTER BY MEANS OF VIBRATIONS INTRODUCTION TO UNIT VI This unit is devoted to the study of electromagnetic waves, which involve light and other vibrations ranging from cosmic rays to long radio waves. It also takes up the study of vibrations in matter, which constitute sound. In many respects, electromagnetic vibrations are similar to vibrations in matter, and for that reason they are studied in the same Unit. Both of these forms of energy differ so much from heat and mechanical energy, studied in Unit V, that it seemed best to study them in a separate Unit. Heat, of course, is a form of vibratory motion, for it will be recalled that heat has been defined as the vibration of The smaller units of matter which make up the molecules molecules. and atoms are likewise believed to vibrate; and, as we shall see, the electron, the unit of electricity, is considered to be a mere wave packet. It is quite proper, therefore, that the study of electricity in Unit VII be preceded by this study of electromagnetic vibrations and of vibrations in matter in the aggregate. 385