Science

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Across
  1. 3. diminution in the density of something
  2. 4. to vibrate
  3. 8. a hollow between two wave crests in the sea
  4. 9. allowing light to pass through
  5. 10. not transparent
  6. 13. sounds caused by the reflection of sound waves from a surface
  7. 14. one thing absorbs or is absorbed by another
  8. 15. surface curved
  9. 16. automatic
  10. 18. curling foamy top of a wave
  11. 19. a space entirely devoid of matter
Down
  1. 1. extending across something
  2. 2. throwing back by a body or surface of light, heat, or sound without absorbing it
  3. 5. change in direction of propagation of any wave
  4. 6. interrelation of electric currents
  5. 7. being compressed
  6. 11. a force acts on objects at a distance
  7. 12. triangular with refracting surfaces at an acute angle
  8. 17. measured from east to west