Part 52

26. (Pg. 112) By what other means may latitude 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 circumstances, 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 ship 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 circumstances 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 circumstances 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 passed the meridian?

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

CONVERSATION X.

ON THE MECHANICAL PROPERTIES OF FLUIDS.

DEFINITION OF A FLUID. DISTINCTION BETWEEN FLUIDS AND LIQUIDS. OF NON-ELASTIC FLUIDS. SCARCELY SUSCEPTIBLE OF COMPRESSION. OF THE COHESION OF FLUIDS. OF THEIR GRAVITATION. OF THEIR EQUILIBRIUM. OF THEIR PRESSURE. OF SPECIFIC GRAVITY. OF THE SPECIFIC GRAVITY OF BODIES HEAVIER THAN WATER. OF THOSE OF THE SAME WEIGHT AS WATER. OF THOSE LIGHTER THAN WATER. OF THE SPECIFIC GRAVITY OF FLUIDS.

MRS. B.

We have hitherto confined our attention to the mechanical properties of solid bodies, which have been illustrated, and, I hope, thoroughly impressed upon your memory, by the conversations we have subsequently had, on astronomy. It will now be necessary for me to give you some account of the mechanical properties of fluids--a science which, when applied to liquids, is divided into two parts, hydrostatics and hydraulics. Hydrostatics, treats of the weight and pressure of fluids; and hydraulics, of the motion of fluids, and the effects produced by this motion. A fluid is a substance which yields to the slightest pressure. If you dip your hand into a basin of water, you are scarcely sensible of meeting with any resistance.

Emily. The attraction of cohesion is then, I suppose, less powerful in fluids, than in solids?

Mrs. B. Yes; fluids, generally speaking, are bodies of less density than solids. From the slight cohesion, of the particles of fluids, and the facility with which they slide over each other, it is inferred, that they have but a slight attraction for each other, and that this attraction is equal, in every position of their particles, and therefore produces no resistance to a perfect freedom of motion among themselves.