Conversations on Natural Philosophy, in which the Elements of that Science are Familiarly Explained Part 3

28. (Pg. 15) From what then do you infer that they possess attraction?

29. (Pg. 15) How do you account for some bodies being hard and others soft?

30. (Pg. 16) What is meant by the term _density_?

31. (Pg. 16) Do the most dense bodies always cohere the most strongly?

32. (Pg. 16) How do we know that one body is more dense than another?

33. (Pg. 16) What is there which acts in opposition to cohesive attraction, tending to separate the particles of bodies?

34. (Pg. 17) What would be the consequence if the repulsive power of heat were not exerted?

35. (Pg. 17) If we continue to increase the heat, what effects will it produce on bodies?

36. (Pg. 17) What body has its dimensions most sensibly affected by change of temperature?

37. (Pg. 17) What power restores vapours to the liquid form?

38. (Pg. 17) What examples can you give?

39. (Pg. 17) How are drops of rain and of dew said to be formed?

40. (Pg. 18) What is meant by a capillary tube?

41. (Pg. 18) What effect does attraction produce when these are immersed in water?

42. (Pg. 18) What is the reason that the water rises to a certain height only?

43. (Pg. 18) Give some familiar examples of capillary attraction.

44. (Pg. 18) In what does _gravitation_ differ from cohesive attraction?

45. (Pg. 18) What causes bodies near the earth's surface, to have a tendency to fall towards it?

46. (Pg. 19) What remarkable difference is there between the attraction of gravitation, and that of cohesion?

47. (Pg. 19) In what instances does the power of cohesion counteract that of gravitation?

48. (Pg. 19) Why will water rise to a less height, if the size of the tube is increased?

49. (Pg. 20) Why do not two bodies cohere, when laid upon each other?

50. (Pg. 20) Can two bodies be made sufficiently flat to cohere with considerable force?

51. (Pg. 20) What is the reason that the adhesion is greater when oil is interposed?

52. (Pg. 21) What other modifications of attraction are there, besides those of cohesion and of gravitation?

CONVERSATION II.

ON THE ATTRACTION OF GRAVITY.

ATTRACTION OF GRAVITATION, CONTINUED. OF WEIGHT. OF THE FALL OF BODIES.

OF THE RESISTANCE OF THE AIR. OF THE ASCENT OF LIGHT BODIES.

EMILY.

I have related to my sister Caroline all that you have taught me of natural philosophy, and she has been so much delighted by it, that she hopes you will have the goodness to admit her to your lessons.

_Mrs. B._ Very willingly; but I did not think you had any taste for studies of this nature, Caroline.

_Caroline._ I confess, Mrs. B., that hitherto I had formed no very agreeable idea either of philosophy, or philosophers; but what Emily has told me has excited my curiosity so much, that I shall be highly pleased if you will allow me to become one of your pupils.

_Mrs. B._ I fear that I shall not find you so tractable a scholar as Emily; I know that you are much biased in favour of your own opinions.

_Caroline._ Then you will have the greater merit in reforming them, Mrs.

B.; and after all the wonders that Emily has related to me, I think I stand but little chance against you and your attractions.

_Mrs. B._ You will, I doubt not, advance a number of objections; but these I shall willingly admit, as they will afford an opportunity of elucidating the subject. Emily, do you recollect the names of the general properties of bodies?

_Emily._ Impenetrability, extension, figure, divisibility, inertia and attraction.

_Mrs. B._ Very well. You must remember that these are properties common to all bodies, and of which they cannot be deprived; all other properties of bodies are called accidental, because they depend on the relation or connexion of one body to another.

_Caroline._ Yet surely, Mrs. B., there are other properties which are essential to bodies, besides those you have enumerated. Colour and weight, for instance, are common to all bodies, and do not arise from their connexion with each other, but exist in the bodies themselves; these, therefore, cannot be accidental qualities?

_Mrs. B._ I beg your pardon; these properties do not exist in bodies independently of their connexion with other bodies.

_Caroline._ What! have bodies no weight? Does not this table weigh heavier than this book; and, if one thing weighs heavier than another, must there not be such a thing as weight?

_Mrs. B._ No doubt: but this property does not appear to be essential to bodies; it depends upon their connexion with each other. Weight is an effect of the power of attraction, without which the table and the book would have no weight whatever.

_Emily._ I think I understand you; it is the attraction of gravity which makes bodies heavy.

_Mrs. B._ You are right. I told you that the attraction of gravity was proportioned to the quant.i.ty of matter which bodies contain: now the earth consisting of a much greater quant.i.ty of matter than any body upon its surface, the force of its attraction must necessarily be greatest, and must draw every thing so situated towards it; in consequence of which, bodies that are unsupported fall to the ground, whilst those that are supported, press upon the object which prevents their fall, with a weight equal to the force with which they gravitate towards the earth.

_Caroline._ The same cause then which occasions the fall of bodies, produces their weight also. It was very dull in me not to understand this before, as it is the natural and necessary consequence of attraction; but the idea that bodies were not really heavy of themselves, appeared to me quite incomprehensible. But, Mrs. B., if attraction is a property essential to matter, weight must be so likewise; for how can one exist without the other?

_Mrs. B._ Suppose there were but one body existing in universal s.p.a.ce, what would its weight be?

_Caroline._ That would depend upon its size; or more accurately speaking, upon the quant.i.ty of matter it contained.

_Emily._ No, no; the body would have no weight, whatever were its size; because nothing would attract it. Am I not right, Mrs. B.?