The cesspool is a tank underground with brick and cemented walls that must not permit any sewage to escape into the soil. Sewage may contain typhoid or other disease germs. We know that these may make water supplies dangerous if they get into the ground and water. If sewage is kept in a tight cesspool the sewage decays and is changed into gas and water. The disease germs will die in time with all their food gone. The gas and water can then safely be carried off underground by a second pipe.

In our houses we prevent unpleasant sewage smells from coming into our rooms by water traps in the waste pipes. These traps are little siphons such as you made in your experiments. These traps can be opened, in case they should become stopped up through carelessness. To keep a trap working, remember:

1. Never to throw rags or strings into basin, tub or toilet.

2. Never to throw grease into a basin—it is wasteful as well as careless.

3. Run washing soda and hot water through the trap once in a while to cleanse it.

4. Always run clean water through the pipes after using a basin, etc.

TO THINK ABOUT

How is the waste from your house removed? What does your city do with its sewage?

What happens to sewage in a cesspool? Why must people be very careful to have cesspools and drains very carefully and tightly built to prevent leaking?

Find the "traps" in your plumbing at home. How do they work? Did the experiment made explain this to you?

Why do houses that haven't been occupied a long time sometimes have a smell of "sewer gas" in them. What happened to the traps?

What can you do to keep your traps at home working?

CHAPTER VII

HOW THE HOUSE WAS LIGHTED

"WHAT did people do before electric lights were invented?” asked Paul. Having spent the afternoon helping Uncle George to put in the wires for the electric lights in the play-house, he felt that he had earned an extra slice of cake for supper.

Mother passed him the cake-plate as she answered, "I suppose the very earliest men of all, who lived in caves and tree-tops, just picked a piece of burning wood out of their fire and carried it for a torch.'

"But that wouldn't be much good if you wanted to read or sew," said Ruth.

"No, but cave and tree-top people have no books and very little clothing, and go to bed with the birds, so they have hardly any need of light in their houses," replied Father.

"Why did you put electric lights into the playhouse, when we have to have gas anyhow to cook with in the kitchen?" asked Ruth.

"Because," said Father, "gas uses up the air— a gas jet may use up as much air as two people. Then, too, it makes the room hot, and besides the gas jet may possibly leak and gas is very poisonous. We have to use it in the kitchen to cook with, but you children will have to be very careful."

"I read about a man who had never seen gas,"

said Paul, "and when he went to bed he blew it out and it killed him."

"There are not many people nowadays who would do that," remarked Mother, "but many people are very careless about turning the

gas, strike your match

first. Don't turn the gas on and then go hunting for a match, as I've seen some people do."

"But, Mother, what did they do before someone invented gas?" persisted Ruth.

"The first lights were lamps," said Mother. "Don't you remember that lovely old Roman lamp that Professor. Fielding showed us? Almost as soon as people began to build real houses they needed lights, for the early houses had very few windows and very tiny ones. The first lamps were made of pottery or bronze and filled with olive oil or some sort of vegetable oil or animal fat, for kerosene was unknown in those days. The wick floated in the oil and made a feeble light."

"Oh, yes,” cried Paul. "Our teacher told us a

story about Cupid and Psyche. She bent over him with a lamp and the oil dropped on him and woke him up and he was angry and went away and left her. She had a lamp just like Professor Fielding's."

"And what did they invent next after lamps?" asked Ruth.

"Well, you see," said Father, "lamps are rather a nuisance, because you have to keep filling them with oil, and, as Paul says, sometimes the oil spills and makes trouble. So someone thought that wax or tallow would be more solid and handy than oil. They melted the wax or tallow and dipped the wick into it, let it cool and harden, then dipped it again and kept on in this way until the candle was as thick as they wanted. That is the reason that we read in old books about 'tallow-dips'-it means candles that were made by dipping the wick into tallow. Nowadays, candles are more often made by laying the wick in molds and pouring the wax or tallow onto it."

"They must have invented candles a long time ago," said Ruth, "for we learned something in Sunday-school about not hiding a light, but putting it in a candlestick, so people could see it."

"Yes," said Uncle George, "candles are so old that nobody knows who made the first one. There is

no prettier, softer light than candle-light, but they flicker and aren't bright enough to work by."

"I like to see them in church," said Ruth.

"All the churches since churches were first built," said Mother, "have used candles. Long before Christ was born candles were burnt in the Jewish temples. You will still see great candle-sticks with seven branches in many Jewish homes.”

"Oh, yes, I saw a beautiful one at Sadie Schwartz's," said Ruth. "Can we have candles in the play-house, Mother?"

"No," said Mother. "I don't like to have you children carry lights about,

for fear of accidents." "Are we going to have a lamp?" asked Paul.

"I'd rather not," said Mother, doubtfully; "you see, lamps have to be cleaned and filled every day, so that they will burn well, and then, too, lamps are rather dangerous." "How are they?" queried Paul.

"In the first place, they tip over easily and the oil blazes up and may set the house on fire. Then, if they are not handled carefully, they sometimes explode."

"How can that happen?" asked Ruth.

"By not blowing them out properly. Do you know how to blow out a lamp?"