772. What is attraction?

Attraction is the tendency of bodies to draw near to each other. It is called attraction, from two Latin words signifying drawing towards.773. How many kinds of attraction are there?

There are five principal kinds of attraction:—

1. The attraction of gravitation.
2. The attraction of cohesion.
3. The attraction of chemical affinity.
4. The attraction of electricity.
5. And capillary attraction.

"Behold, the nations are as a drop of a bucket, and are counted as the small dust of the balance: behold, he taketh up the isles as a very little thing."—Isaiah xl.

774. Why do all bodies heavier than the air fall to the earth?

Because they are influenced by the attraction of gravitation, by which all bodies are drawn towards the centre of the earth.775. Why do bodies lighter than the air ascend?

Because the air, being a denser body, obeys the law of attraction, and in doing so displaces lighter bodies that interfere with its gravitation.776. Why do fragments of tea, and bubbles floating upon the surface of tea, draw towards each other, and attach themselves to the sides of the cup?

Because they are influenced by the attraction of cohesion.

Cohesion.—The act of sticking together.777. Why will a drop of water upon the blade of a knife leave a dark spot?

Because the iron of the knife attracts the oxygen of the water, by chemical affinity; and the two substances form a thin coating of oxide of iron.

Affinity.—Attraction between dissimilar particles through which they form new compounds.778. Why do clouds sometimes move towards each other from opposite directions? and779. Why do light particles of matter attach themselves to sealing wax, excited by friction?

Because they are moved by the attraction of electricity.780. Why will a towel, the corner of which is dipped in water, become wet far above the water?

Because the water is conveyed up through the towel, by capillary attraction. The atoms of the water are attracted by the threads of the towel, and drawn up into the small spaces between the threads.

Capillary.—Resembling a hair, small in diameter.

"He stretcheth out the north over the empty place, and hangeth the earth upon nothing."—Job xxvi.

781. Why do small bodies floating upon water move towards larger ones?

Because the attractive power of a large body is greater than that of a small one. As each atom of matter has inherent power of attraction, it follows that a large aggregation of particles must attract in proportion to the number of those particles.782. Why do clouds gather around mountain tops?

Because they are attracted by the mountains.783. Why would a piece of lead tied to a string, and let down from a church steeple, incline a little from the perpendicular towards the church?

Because the masses of stone of which the church is built would attract the lead.784. How can man weigh the earth?

By observing what is called the deflection of small bodies when brought within given distances of larger bodies, the degree of attraction exercised by the large body upon the smaller one becomes known. This attraction of the large body exercised over the smaller body is an opposing influence, acting against the earth's attraction of the small body, which is drawn out of its course: it constitutes a natural balance between the influence of the earth and another body, acting in opposition to it. Founded upon these, and some other data, man can weigh the earth, and give a morally certain result!

Deflection.—The act of turning aside.785. How can man weigh the planets?

The planets exercise as certain an influence upon each other as do two pieces of wood floating upon a basin of water. As the planetary bodies fly through their prescribed orbits, and approach nearer to, or travel further from, each other, they are observed to deviate from that course which they must have pursued but for the increase or the decrease of some influence of attraction. By making observations at various times, and by comparing a number of results, it is possible to weigh any planetary body, however vast, or however distant.

"Is not God in the height of the heaven? and behold the height of the stars, how high they are?"—Job xii.

786. How can man measure the distances of the planets?

By making observations at different seasons of the year, when the earth is in opposite positions in her orbit; and by recording, by instruments constructed with the greatest nicety, the angle of sight, at which the planetary body is viewed; by noticing, also, the various eclipses, and estimating how long the first light after an eclipse has ceased reaches the earth, it is possible to estimate the distances of heavenly bodies, no matter how far in the depths of the universe those orbs may be.787. What are the opinions founded upon estimates respecting the magnitude of the sun?

The diameter of the sun is 770,800 geographical miles, or 112 times greater than the diameter of the earth; its volume is 1,407,124 times that of the earth, and 600 times greater than all the planets together; its mass is 359,551 times greater than the earth; and 738 times greater than that of all the planets. A single spot seen upon its surface has been estimated to extend over 77,000 miles in diameter, and a cluster of spots have been estimated to include an area of 3,780,000 miles.788. What is the weight of the earth?

The earth has a circumference of 25,000 miles, and is estimated to weigh 1,256,195,670,000,000,000,000,000 tons.789. What is the specific gravity of a body?

It is its weight estimated relatively to the weights of other bodies.790. What determines the force with which bodies fall to the earth?

Generally speaking, their specific gravity, which is proportionate to the density, or compactness of the atoms of which they are composed.791. Why does a feather fall to the earth more gradually than a shilling?

Because the specific gravity of the feather and of the shilling is relative to that of the air, the medium through which the feather and the shilling pass. If there were no air, a shilling and a feather dropped at the same time from a height of forty miles, would reach the earth at the same moment.