Light, besides traveling faster than sound, can travel a great deal farther. Lightning may be so far off that you can not hear the thunder. The light reaches your eye, but the sound dies away before it reaches your ear.
Light of burning substances.
Most of our light, I have said, comes from the sun; but much light comes from burning substances—burning wood, coal, oil, tallow, gas, &c.
Fire-flies.
Shining flowers.
Light-wood.
Light is made by some animals. The glow-worm gives out a soft and beautiful light. The fire-fly sparkles as it flies about in the evening. In Cuba and in South America ladies wear in their hair as ornaments, in evening parties, some small insects that give a very brilliant light. Sometimes the sea sparkles beautifully with light, which is made by multitudes of very little animals in it. We see this light often in the wake of a vessel, or behind the wheel of the steamer, or in the water that falls from the lifted oar. It is when the water is disturbed in some way that these animals make their light. There are some flowers in very warm countries that shine in the night. You have seen what is called light-wood. This is decayed wood, and it is something in the decay that makes the light. Light is also sometimes given out by animal substances that are decaying. It is most often seen in putrid fish.
Phosphorus.
It is supposed that in all these cases the light is made by phosphorus, the same substance that lights so easily in the Lucifer match. This curious substance is commonly kept in water. If a stick of it be taken out of the water in the evening, it appears lighted like a glow-worm; and if you rub it upon any thing, the streaks of it will give a brilliant white light. Sometimes, on rubbing a match, if it does not take fire, you see for a little time lighted streaks where you rubbed it. This is caused by the phosphorus rubbed off from the match. When the match burns, you do not see these lighted streaks, for the same reason that you do not see the stars when the sun shines.
Questions.—What is the chief use of light? How do we see? How do we see things that do not make light? How do we see things in a mirror? How is the image in the mirror like that in the eye? What difference is there in things in reflecting light? What is said about the light of the moon and the stars? Why can not we see the stars in the daytime? Why can we see the moon in the daytime? What is mentioned which shows that light is often reflected many times before it comes into the eye? Tell what is said about an assembly all looking at a speaker. What effect has light upon plants and animals? What is said about living in dark rooms? How long is light in coming from the sun? Give some examples which show that it travels faster than sound. Can sound go as far as light? From what besides the sun does light come? Tell about the fire-flies—the sparkling that we often see in the sea—light-wood. What is said about phosphorus?