Pupil. I remember it well. But what am I to understand by attraction of gravitation?
Tutor. The sun, being the largest body, attracts the earth and all the other planets, they gravitate or have a tendency to approach the sun; the earth being larger than the moon attracts her, and she gravitates towards the earth; the planets are attracted by and gravitate towards each other; a stone when thrown from the earth, by its attraction and the gravitating power or weight of the stone, is brought to the earth again; the waters in the ocean gravitate towards the center of the earth; and it is by this power we stand on all parts of the earth with our feet pointing to the center.
Pupil. This information affords me great pleasure.
Tutor. Having mentioned attraction of magnetism, electricity, and gravitation, it may not be amiss to inform you of another kind, called attraction of cohesion.
Pupil. Any thing which tends to my improvement, I shall be obliged to you to communicate.
Tutor. By attraction of cohesion is meant that property in bodies which connects or firmly unites the different particles of matter of which the body is composed.
Pupil. Pray, Sir, inform me what you mean by the laws of attraction?
Tutor. You are to understand, 1st. That attraction decreases as the squares of the distances between the centers of the attracting bodies increase.
Pupil. I must beg you, Sir, to explain to me the meaning of the squares of the distances.
Tutor. Any number multiplied into itself is a square number, thus 1 is the square of 1; 4 is the square of 2; 9 is the square of 3, and so on, because 1 multiplied into itself is 1; 2 by 2 is 4; 3 by 3 is 9, &c. Now suppose, that when the planet is at B (Plate II. fig. 4.) it is twice as far from the sun as it is at A: how much more will it be attracted by the sun at A than at B?