WHY LEAD IS HEAVIER THAN CORK.
Monsieur Roger continued in these words:
"We say that a body has density when it is thick and packed close. We
give the name of density to the quantity of matter contained in a body
of a certain size.
"Let us suppose that this bit of lead has the same bulk--that is to say,
that it is exactly as big--as the cork. Suppose, also, that we have a
piece of gold and a piece of stone, also of the same bulk as the cork,
and that we weigh each different piece in a pair of scales. We would
find that cork weighs less than stone, that stone weighs less than lead,
and that lead weighs less than gold. But, in order to compare these
differences with each other, it has been necessary to adopt a standard
of weight.
"I now return to Miss Miette's question,--'Why is lead heavier than
cork?'--a question to which I had solemnly answered, 'Because its
density is greater.' Miss Miette must now understand that cork, weighing
four times less than water, cannot sink in water, although that process
is very easy to lead, which weighs eleven times more than water. And
yet," said Monsieur Roger, "the problem is not perfectly solved, and I
am quite sure that Miss Miette is not entirely satisfied."
Miss Miette remained silent.
"I was not mistaken. Miss Miette is not satisfied," said Monsieur Roger;
"and she is right,--for I have not really explained to her why lead is
heavier than cork."
Miss Miette made a gesture, which seemed to say, "That is what I was
expecting."
"I said just now," continued Monsieur Roger, "that the density of a body
was the quantity of matter contained in this body in a certain bulk. Now
does Miss Miette know what matter is?"
"No."
"No! Now, there is the important thing: because, in explaining to her
what matter is, I will make her understand why lead is heavier than
cork."
"Well, I am listening," said Miette.
And Master Paul respectfully added, in an undertone, "We are listening."
Monsieur Roger continued:
"The name of 'bodies' has been given to all objects which, in infinite
variety, surround us and reveal themselves to us by the touch, taste,
sight, and smell. All these bodies present distinct properties; but
there are certain numbers of properties which are common to all. Those
all occupy a certain space; all are expanded by heat, are contracted by
cold, and can even pass from the solid to the liquid state, and from the
liquid to the gaseous state. They all possess a certain amount of
elasticity, a certain amount of compressibility,--in a word, there exist
in all bodies common characteristics: so they have given a common name
to those possessing these common properties, and called that which
constitutes bodies 'matter.' Bodies are not compact, as you may imagine.
They are, on the contrary, formed by the union of infinitely small
particles, all equal to each other and maintained at distances that are
relatively considerable by the force of attraction.
"These infinitely small particles have received the names of atoms or
molecules. Imagine a pile of bullets, and remark the empty spaces left
between them, and you will have a picture of the formation of bodies. I
must acknowledge to you that no one has yet seen the molecules of a
body. Their size is so small that no microscope can ever be made keen
enough to see them. A wise man has reached this conclusion: That if you
were to look at a drop of water through a magnifying instrument which
made it appear as large as the whole earth, the molecules which compose
this drop of water would seem hardly bigger than bits of bird-shot.
Still, this conception of the formation of bodies is proved by certain
properties which matter enjoys. Among these properties I must especially
single out divisibility. Matter can be divided into parts so small that
it is difficult to conceive of them. Gold-beaters, for instance, succeed
in making gold-leaf so thin that it is necessary to place sixty thousand
one on top of the other to arrive at the thickness of an inch. I will
give you two other examples of 'divisibility' that are still more
striking. For years, hardly losing any of its weight, a grain of musk
spreads a strong odor. In a tubful of water one single drop of indigo
communicates its color. The smallness of these particles of musk which
strike the sense of smell and of these particles of indigo which color
several quarts of water is beyond our imagination to conceive of. And
these examples prove that bodies are nothing but a conglomeration of
molecules. Now, if lead is heavier than cork, it is because in an equal
volume it contains a far more considerable quantity of molecules, and
because these molecules are themselves heavier than the molecules of
cork. And now I shall stop," said Monsieur Roger, "after this long but
necessary explanation. I will continue on the day when Miss Miette will
present to me the famous air-pump."
"That will not be very long from now," said Miss Miette to herself.
[Illustration]
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