tail. The duck spreads a film of this oil all over the surface of its feathers. Now oil and water will not mix, so the water cannot get through this oil to wet the duck’s feathers. Besides, the oil slips past the water, making swimming easier. The next time you go swimming oil your back and the water will roll from it just as it does from a duck’s back.
WHY FROZEN WATER BURSTS PIPES
Nearly everything we know is expanded or swollen by heat, and contracted or shrunken by cold. But water is queer. It’s particles huddle closest together, and fill the smallest amount of space when in a liquid state. And it is expanded by both heat and cold. When heated to the boiling point and turned into vapor it takes up the most space. Steam confined in a boiler bursts iron walls, 1f it can get out in no other way. So in freezing, water expands to a larger bulk. That is why ice floats in water. If the water happens to freeze in a pipe, where there is no room for it to expand, it bursts the pipe. Some people think the thawing bursts the pipe, but the thawing only shows us the places where the frost burst it. You know a quiet pond freezes more quickly than a running stream. One way to keep your pipes from bursting in zero weather, is to open a faucet a little way. That keeps the water flowing so it is less likely to freeze.
WHY WE ARE TANNED BY THE SUN
"To tan" has two meanings. One is to turn anything a yellowish-brown color. The other meaning is to toughen and harden skins into leather. In the making of leather, both the toughening and the coloring are results of the processes of tanning. So it seems to be in the case of exposure of our skins to a great deal of hot sunshine. When a city child, who has lived in the house and in shaded streets, goes on a vacation to a farm or the seashore in mid-summer, the first effect of the exposure to sun rays is burning of the tender skin. This would not do at all, for burned skin blisters and peels. Different things in our bodies always rush to any injured parts to heal and protect them. A dark surface absorbs heat better than a light one. So to protect the skin from the heat, a dark pigment or paint is formed by blood cells and sunbeams acting together. This not only darkens the skin, but toughens it, too. Our skins are really "tanned" some-
