t can get so much closer to the oil
or water film and because this film flows partly around each dust
particle and holds it by the force of adhesion. This is why your face
gets much dirtier when it is perspiring than when it is dry.

_APPLICATION 12._ Explain why cobwebs do not fall from the
ceiling; why dust clings to a wet broom; why a postage stamp
does not fall off an envelope.

INFERENCE EXERCISE

Explain the following:

41. There are no springs on the tops of high mountains.

42. People used to shake sand over their letters after writing
them in ink.

43. People used to make night lights for bedrooms by pouring
some oil into a cup of water and floating a piece of wick on
the oil. The oil always stayed on top of the water, and went
up through the wick fast enough to keep the light burning.

44. Your face becomes much dirtier when you are perspiring.

45. Ink bottles are usually made with wide bases.

46. When you spill water on the floor, you cannot wipe it up
with wrapping paper, but you can dry it easily with a cloth.

47. Oiled mops are used in taking up dust.

48. Cake will stick to a pan unless the pan is greased.

49. Although the earth turns completely over every day, we
never fall off it.

50. Signs are fastened sometimes to windows or to the wind
shields of automobiles by little rubber "suction caps."

SECTION 8. _The force that makes a thing hold together: Cohesion._

What makes rain fall in drops?

Why are diamonds hard?

You have not yet touched any of the most dangerous switches on the
imaginary switchboard of universal laws. But if your experience in
turning off the capillary attraction and adhesion switches did not
discourage you, you might try turning off the one beside them labeled
COHESION:

[Illustration: FIG. 22. El Capitan, Yosemite Valley, California.
If the force of cohesion were suspended, a mountain like this would
immediately become the finest dust.]

Things happen too swiftly for you to know much about them. The house
you are in falls to dust instantly. You fall through the place where
the floor has been; but you do not bump on the cement basement floor
below, partly because there is no such thing as a hard floor or even
hard ground anywhere, and partly because you disintegrate--fall to
pieces--so completely that there is nothing left of you but a grayish
film of fine d