AIR is the medium by which light is diffused. Men who have been up in balloons say that the higher they went up the blacker the sky became; and no doubt above the air it is perfect darkness. Although the sun's rays pour through the vast space above, yet they give no light, except upon the objects on which they directly fall; for there is no air for them to illuminate.

Light travels very fast. It takes it only eight minutes to come from the sun to us, although the distance is about ninety one million miles. The color of the air is light blue, and what we call "blue sky" is simply blue air. The grayish or white appearance of the sky is caused by clouds, or vapor. Clouds are masses of mist floating in the air; and are of different sizes, forms, and colors. Sometimes they assume many strange and wonderful shapes. And persons with vivid imaginations often fancy they see curious forms and figures in the sky. Clouds generally appear the most beautiful when the last rays of the setting sun light up the west, and paint the sky with burning colors of crimson and gold.

Clouds are drawn from the water and moist soil of the earth by the heat of the sun. On an average, they are about two and a half miles from the earth; and they descend to the earth in the form of rain.

Hail is frozen rain, and snow is frozen mist. There are portions of the earth where rain never falls, and other parts where it rains nearly all the time. Some parts of the earth are always covered with snow, and other parts have none at all. Snowflakes, when viewed through a microscope, exhibit forms of exquisite beauty. In the polar-regions, they assume the most beautiful and varied forms.

In these regions, strange lights are often seen in the sky, such as shining balls and crosses of fire, and a crown of red light called the aurora borealis, or polar light. This is a beautiful light, and exhibits various colors, from a white to a blood red. It often assumes fantastic shapes, but is usually in streams. It is frequently seen in our own country, but it never appears as beautiful as in the North.

The first appearance of the Northern Lights in this country after its settlement, was on the evening of Dec. 11, 1719, and as the people had never heard about them, they caused much alarm. One writer describes them thus: "About 8 o'clock there arose a bright red light, like that which arises from a house on fire. It spread itself through the heavens from east to west, and streamed with white flashes of light down to the horizon. It was the brightest in the middle, and its appearance was dreadful; sometimes it looked like fire, and sometimes like blood. It lasted about an hour, and many thought the day of Judgment was at hand."

It is not certainly known what causes these lights in the heavens, and no wonder they create terror, when they stream "Like living things with flaming wings, Across the sunless sky."



ON pleasant evenings, the sky appears to be studded with stars, and children often speak of them as being in the air. This is a mistake; the stars are thousands of miles above the air, in a vast ocean of space which no man has been able to fathom.

Sound is produced by the vibration of the air. If there were no air, there would be no sound; consequently, above the air it must be as still as the grave; and if the sun were to explode, it would do so in silence.

A gun fired on the summit of a high mountain sounds no louder than a firecracker.

 In deep mines it is just the reverse, and the air is so dense that the workmen are obliged to talk in whispers, otherwise their voices would sound unpleasantly loud. In the arctic regions the air is so clear, cold, and still, that it carries sound a great distance, and persons one and a half miles from each other can converse together.

Wood is a good conductor of sound. In Sweden, deaf men and women may be seen sitting in church holding in their mouths long wooden sticks, which touch the pulpit. 

By doing this they are enabled to hear much of the sermon. There is a difference in individuals in their power of hearing.

The bat makes a low, crying noise, which thousands of people cannot hear. One writer says that he believes there are "sounds in the air of which we have no idea; and if our ears could be quickened we would hear the songs of angels, whereas we now hear only the feeble accents of our own broken prayers." He says, "All nature tends to music. A bullet whistling through the air sings as sweetly as a bird. The murmur of the leaves of the trees in the breeze, the rumble of the great city, the rushing of waters, the singing of birds, the sighing of the wind, and all the confused noises of nature, when softened by distance, are said to be upon one pitch the key of F."  Damp air is a better conductor of sound than dry air; hence music sounds best in the night. When sound strikes a hard surface it is sent back, and the reflected sound is called an echo. In a certain place in Scotland, there is a remarkable echo. If a tune is played or sung, the echo repeats it correctly, and then keeps repeating it in a lower key until it dies away. An echo in Italy repeats the same sound thirty times. 

When a cannon is fired on the shores of Echo Lake, in New Hampshire, the sound produces an echo, which is like a peal of thunder. In St. Paul's church, in London, a whisper at one side of the dome is carried a considerable distance to the opposite side. 

If it were not for the resistance of the air, all bodies would fall to the earth with equal rapidity. If there were no air, a bullet and a feather would fall to the ground in the same space of time. This may seem strange to you, but it is a well, established fact.



MEN and animals live on the oxygen in the air, and send out from their lungs carbonic acid gas, which, when unmixed with oxygen, is a deadly poison. You may think that the breathing of the many millions of creatures in the world, would, after a time, consume all the oxygen in the air, and leave nothing but carbonic acid gas, nitrogen, and vapor. But the Creator of all things with infinite wisdom has provided for this want. Plants breathe, as well as animals; but in the daytime, when under the influence of the sun, they live on carbonic acid gas, and send out oxygen. Thus animals and vegetables meet each other's wants, and as long as the two exist together there need be no fear of their suffering for want of air.

Nitrogen was formerly called "Life destroyer," because when unmixed with oxygen, it is destructive to animal life. It is a little lighter than oxygen, but readily unites with it, forming very different substances, according to the proportions of the mixture. Air is very mild, but aqua-fort is --a combination of the same elements is so harsh an acid that it readily dissolves metals.  I have told you a few facts concerning the composition of the air, and I will now note some things in regard to its properties. The air is transparent; that is, it can be seen through. Vapor dims its clearness. When it is free from vapor, distant objects appear much nearer than they really are. The air is a, fluid; that is, it presses in all directions, can be easily moved, and is capable of supporting light bodies.

The air has weight. A cubic foot weighs about one ounce. Every person carries the weight of about fourteen tons of air upon his head. We do not feel the pressure because it is uniform on all sides and the air within our bodies counterbalances that without. The air is elastic; that is, when compressed by force, it returns to its original shape when the pressure is removed.

The air is supposed to extend about fifty miles above the earth. It grows thinner as we ascend. Men who go up in balloons are obliged to carry much clothing with them, because the thinness of the air renders it intensely cold. Humboldt, the great traveler, says that when he attempted to ascend very high mountains, blood gushed from his eyes, ears, and lips. This was owing to the lightness of the air.