Conversations on Natural Philosophy, in which the Elements of that Science are Familiarly Explained Part 28

_Emily._ Pray what is the reason that the tide is three-quarters of an hour later every day?

_Mrs. B._ Because it is twenty-four hours and three-quarters before the same meridian, on our globe, returns beneath the moon. The earth revolves on its axis in about twenty-four hours; if the moon were stationary, therefore, the same part of our globe would, every twenty-four hours, return beneath the moon; but as during our daily revolution, the moon advances in her orbit, the earth must make more than a complete rotation, in order to bring the same meridian opposite the moon: we are three-quarters of an hour in overtaking her. The tides, therefore, are r.e.t.a.r.ded, for the same reason that the moon rises later by three-quarters of an hour, every day.

We have now, I think, concluded the observations I had to make to you on the subject of astronomy; at our next interview, I shall attempt to explain to you the elements of hydrostatics.

Questions

1. (Pg. 108) In what time does the moon revolve round the earth? what is the inclination of her orbit? and how does she accompany the earth?

2. (Pg. 108) As the moon revolves round the earth, and also accompanies it in its annual revolution, in what form would you draw the moon's...o...b..t?

3. (Pg. 109) What causes the moon always to present the same face to the earth, and what must be the length of a day and night to its inhabitants?

4. (Pg. 109) Can the earth be seen from every part of the moon, and will it always exhibit the same appearance?

5. (Pg. 109) What are the changes of the moon called?

6. (Pg. 109) How are these changes explained by fig. 2. plate 11?

7. (Pg. 109) What is meant by her first quarter?

8. (Pg. 109) What by her being horned, and her being gibbous?

9. (Pg. 109) What by her being full?

10. (Pg. 109) What by her third quarter?

11. (Pg. 110) What is meant by her conjunction?--what by her being in opposition?--what by her quadratures?

12. (Pg. 110) By what are eclipses of the sun caused?

13. (Pg. 110) What causes eclipses of the moon?

14. (Pg. 110) What is meant by the moon's nodes?

15. (Pg. 110) Why do not eclipses happen at every new and full moon?

16. (Pg. 110) What causes partial eclipses of the moon?

17. (Pg. 110) When the moon is exactly in one of her nodes, what length of time will she be eclipsed?

18. (Pg. 110) Are total eclipses of the sun frequent, and when they happen what is their extent?

19. (Pg. 111) What does this prove respecting the size of the moon?

20. (Pg. 111) What is shown in fig. 1, plate 12?

21. (Pg. 111) How are lunar eclipses visible, and what is proved by their duration?

22. (Pg. 111) What is ill.u.s.trated by fig. 2, plate 12?

23. (Pg. 111) What remark is made respecting those planets which have several moons?

24. (Pg. 111) What use is made of the eclipses of the satellites of Jupiter?

25. (Pg. 112) How is the lat.i.tude of a place usually found?

26. (Pg. 112) By what other means may lat.i.tude be found?

27. (Pg. 112) From what is longitude reckoned?

28. (Pg. 112) How does the rotation of the earth upon its axis, govern the time at different places?

29. (Pg. 113) What two circ.u.mstances, if known, will enable you to find your longitude from a given place?

30. (Pg. 113) By what means may a captain find the time at London, and in the place where his s.h.i.+p may be?

31. (Pg. 113) How may the eclipses of Jupiter's satellites be used to find the longitude?

32. (Pg. 113) Give an example.

33. (Pg. 114) How will you know whether the longitude is east or west?

34. (Pg. 114) What is meant by the transit of a planet?

35. (Pg. 114) Why can we see transits of Venus and Mercury only?

36. (Pg. 114) By what are tides caused?

37. (Pg. 114) Why is not a similar effect produced on the land?

38. (Pg. 115) In what two parts of the world is it high water at the same time?

39. (Pg. 115) What circ.u.mstances respecting the decrease of attraction are taken into account, in explaining the tides?

40. (Pg. 115) How are the high tides at A and D, and the low ones at B and C, in fig. 3. pl. 12, accounted for?

41. (Pg. 116) Has the sun any influence on the tides, and why is it less than that of the moon?

42. (Pg. 116) What is meant by spring tides, and how are they produced?

43. (Pg. 116) What by neap tides, and how are they caused?

44. (Pg. 116) What circ.u.mstances affect the time of the tide in rivers, bays, &c.?

45. (Pg. 117) Why in the open ocean, is it high water, some hours after the moon has pa.s.sed the meridian?

46. (Pg. 117) Why are the tides three-quarters of an hour later every day?