Moisture

: STORIES FROM PHYSICS
: Fables For Children, Stories For Children, Natural Science Stori

I.



Why does a spider sometimes make a close cobweb, and sit in the very

middle of its nest, and at other times leave its nest and start a new

spider-web?



The spider makes its cobweb according to the weather, both the present

and the future weather. Looking at a spider, you can tell what kind of

weather it is going to be: if it sits tightly in the middle of the

cobweb and does no
come out, it means that it is going to rain. If it

leaves the nest and makes new cobwebs, it is going to clear off.



How can the spider know in advance what weather it is going to be?



The spider's senses are so fine that as soon as the moisture begins to

gather in the air,--though we do not yet feel it, and for us the weather

is clear,--for the spider it is already raining.



Just as a naked man will feel the moisture, when a man in his clothes

does not, so it is already raining for a spider, while for us it is only

getting ready to rain.





II.



Why do the doors swell in the winter and close badly, while in the

summer they shrink and close well?



Because in the fall and winter the wood is saturated with water, like a

sponge, and spreads out, while in the summer the water comes out as a

vapour, and the wood shrinks.



Why does soft wood, like aspen, swell more, and oak less?



Because in the hard wood, in the oak, the empty places are smaller, and

the water cannot gather there, while in the soft wood in the aspen,

there are larger empty places, and the water can gather there. In rotten

wood these empty places are still larger, and so rotten wood swells most

and shrinks most.



Beehives are made out of the softest and rottenest wood; the very best

are made from rotten willow wood. Why? Because the air passes through

the rotten wood, and in such a hive the bees feel better.



Why do boards warp?



Because they dry unevenly. If you place a damp board with one side

toward the stove, the water will leave it, and the board will contract

on that side and will pull the other side along; but the damp side

cannot contract, because it is full of water, and so the whole board

will be bent.



To keep the floors from warping, the dry boards are cut into small

pieces, and these pieces are boiled in water. When all the water is

boiled out of them, they are glued together, and then they never warp

(parquetry).



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