"To be" and its functions. "To have" and its functions

12. Having an equatorial diameter of 74,000 mi, Saturn is sur­rounded by great rings lying in the plane of its equator.
13. A man pulled by the Earth with a force of 160 Ib is said to weigh 160 Ib.
14. Interplanetary spacecraft using nuclear propulsion are expected to be reduced in weight in comparison with nuclear rockets.
15. The word plasma was first used to denote a gas in which an important fraction of the molecules are dissociated into ions and electrons, the gas as a whole remaining electrically neutral.
16. Newton believed that the acceleration of the Moon in its orbit differed in no essential respect from the acceleration of parti­cles acted on by the Earth's gravities.
17. The electromagnetic wave theory of radiation, based on the work of Maxwell and Hertz, was so successful that we must try to apply it to the spectrum just described.
18. Radiation goes through space and when absorbed, it agitates the molecules of the absorbing material so that it is converted into heat energy.
19. The reader is familiar with the great technical importance of electron emission, as applied in radio tubes.
20. Molecules and atoms are in a continual state of motion, with an average velocity depending on the temperature.
21. Having seen how the electrons in the ionosphere are pro­duced by solar radiation, let us ask how the different layers affect the travel of radio waves in the different frequency ranges.
22. This radiation, being little absorbed, penetrates to the D-region and there joins with the X-rays in providing ionization.
23. The alkali atoms have the lowest energies of ionization, indicating that their electronic structures change to a rare-gas structure.
24. The emissive type of the photoelectric cell as used in telegraph and television systems is similar in appearance to the ordinary thermoionic valve.
25. A screen material of a different category from those so far discussed is white crystalline potassium chloride: this substance darkens when bombarded with electrons.