A Guide To The Scientific Knowledge Of Things Familiar Part 81

A. They put an _egg into their brine_. If the egg _sinks_ the brine is _not strong enough_, if the egg _floats_ it _is_.

Q. _Why will the EGG SINK if the brine be NOT STRONG enough for pickling?_

A. As an egg is _heavier than water_, it will _sink_ if immersed therein; but if as much _salt_ be added as the water can dissolve, the egg will _float_.

Q. _Why will the EGG FLOAT in strong BRINE?_

A. Because the specific gravity of _salt and water_ is greater than that of water _only_.

Q. _Why do persons SINK in water when they are UNSKILFUL SWIMMERS?_

A. 1st--Because (in their floundering about) they _take in water_ at their nose and mouth, which makes them _heavier_:

2ndly--FEAR _contracts the body_; and as the body is compressed by fear into a smaller compa.s.s, it becomes _heavier_: and

3rdly--The water and fear _take away the breath_; and when the breath is taken from the body, its _bulk is reduced_, and it becomes _heavier_.

Q. _Why can QUADRUPEDS swim MORE EASILY than MAN?_

A. 1st--Because the _trunk_ of a quadruped is _lighter than water_, and this is the greatest part of them:

2ndly--The _position_ of a beast in water is a _natural_ one.

Q. _Why is it MORE DIFFICULT for a MAN to swim than for a BEAST?_

A. Because the _head and limbs_ of a man (like those of a beast) are _heavier_ than water, and these compose more than _half his body_:

2ndly--The _position_ of a man in water is _unnatural_ to him.

Q. _Why can FAT men SWIM more EASILY than SPARE men?_

A. _Fat is lighter than water_; and the _fatter_ a man is, the more _buoyant_ will he be.

Q. _How are FISHES able to ASCEND to the SURFACE of water?_

A. Fishes have an _air-bladder_ near their abdomen: when this bladder is _filled with air_, the fish increases in size; and (being lighter) ascends through the water to its surface.

Q. _How are fishes able to DIVE in a minute to the BOTTOM of a stream?_

A. They _expel the air_ from their air-bladder; in consequence of which, their _size is diminished_, and they sink instantly.

CHAPTER XXVII.

LIGHT.

Q. _What is LIGHT?_

A. Rapid undulations of a fluid called ether, striking on the optic nerve of the eye. (_See p. 46._)

The _heat_ of fire or of the sun sets the atoms of _matter_ in motion; and these atoms, striking against the fluid _ether_, cause it to undulate.

Q. _How FAST does LIGHT TRAVEL?_

A. Light travels so fast, that it would go eight times round the earth, while a person counts "ONE."

Q. _Does ALL light travel equally fast?_

A. Yes; the light of the sun, or the light of a candle, or the light from houses, trees, and fields.

Q. _Where does the LIGHT of HOUSES, TREES, and FIELDS come from?_

A. The light of the _sun_ (or of some lamp or candle) is _reflected from their surfaces_.

Q. _Why are SOME surfaces BRILLIANT like gla.s.s and steel, and OTHERS DULL like lead?_

A. Those surfaces which _reflect the most light_, are the most _brilliant_; and those which _absorb_ light are _dull_.

Q. _What is meant by REFLECTING LIGHT?_

A. Throwing the rays of light _back again_, from the surface on which they light.

Q. _What is meant by ABSORBING LIGHT?_

A. Letting the rays of light _sink below the surface_ which they touch, so as not to be seen.

Q. _Why can a THOUSAND persons SEE the SAME OBJECT at the same time?_

A. Because it throws off from its surface _an infinite number of rays in all directions_; and one person sees _one_ portion of these rays, and another person _another_.