SCIENCE PRIMERS,

INTRODUCTORl

PROF. HUXLEY

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INTRODUCTORY.

PROFESSOR HUXLEY, F.R.S.

CANADA PUBLISHING CO.,

(limited.)

Entered according to the Act of the Parliament of Canada, in
the y cap One Thousand Eight Hundred and Eighly-one by
MACMII.LAH & Co., London, in the Office of the Minister
of Agriculture.

»9

TABLE OF CONTENTS.

ART SECT

I.' NATURE AND SCIENCE.

PAGi

1. " Sensations and Things . . 5

2. " Causes and Effects ... . • • 5

3. '■" The reason Why. Explanation 6

4. " Properties and Powers 7

5. ■" Artificial and Natural Objects, Nature .... 8

6. " Artificial Things are only Natural Things shaped and

brought together or separated by Men. ... 8

7. ■" Many Objects and Chains of Causes and Effects in Nature

are out of our reach lo

8. " The Order of Nature : nothing happens by Accident, and

there is no such thing as Chance 10

9. " Laws of Nature ; Laws are not Causes . . . .12

10. " Knowledge of Nature is the Guide of Practical Conduct. 14

11. " Science: The Knowledge of the Laws of Nature obtained

by Observation, Experiment, and Reasoning . . .16

n. MATERIAL OBJECTS.— (A.).MINERAL BODIES.

12. " The Natural Object Water 19

13. "A Tumbler of Water 20

14. " Water occupies Space ; it offers Resistance; it has Weig^ht;

and is able to transfer Motion which it has acquired; it is

therefore a form of Matter 20

15. " Water is a liquid 21

j6. " Water is almost incompressible ...... 22

17. " The meaning of Weight . . . . . .24

18. " Gravity and Gravitation 25

" The cause of Weight : Attraction : Force . . .27

" The Weight of Water is Proportioned to its Bulk . . 28

«i. " The Measuring of Weights. The Balance. . . .29
«2. " The Weight of the same Bulk or Volume of Water is Con-
stant under the same conditions. Mass. Density . 30
23. '■ Equal Volumes of Different Things under the same cir-
cumstances, have Different Weights: the Density of Dif-
ferent Bodies is Different 32

14. '■ The Meaning of Heavy and Light — Specific Gravity . 33

25. " Things of greater Specific Gravity than Water sink in

Water ; Things of less Specific Gravity float . . 34

a6. " A Body which Floats in Water always occupies as much

Space beneath the level of the Surface of the Water as is
equal to the Volume of Water which weighs as much as
that Body; in other words, it displaces its own Weight of

Water 3*

»7. " Water Presses in all Directions 37

38. " The Transference of Motion by Moving Water : the Mo-

mentum of Moving Water ... ... 40

29. ' The Energy of Moving Water 43

30. " The Properties of Water are Constant . . . .47

31. " Increase of Heat at first causes Water to Increase in Vol-

ume 48

32. " Increase of Heat at length causes Water to become Steam. 50

33. " The takin}^ away of Heat from Steam causes the Steam to

change mto Hot Water 5*

34. " When Water is changed into Steam, its Volume becomes

about 1,700 times greater than it was at first. . .51

35. " Gases or Elastic Fluids. Air 52

36. "' Steam is an Elastic Fluid or Gas 54

37. " Gases and Vapours 55

^8. " The Evaporation of Water at ordinary Temperatures . 56

3y " When Hot Water is cooled, it Contracts lo begin with, but

after a time Expands . • • 5/

TABLE Ofi COMTENT^.

40. II. Water cooled still further becomes the transparent brittle

solid Ice 58

41. " Ice has less Specific Gravity than the Water from which it

was formed 59

42. " Hoar Frost is the Gaseous Water which exists in the At-

mosphere, condensed and converted into Ice Crystals . 60

43. " When Ice is warmed it begins to change back into Water

as soon as the Temperature reaches 32°. . . .61

44. " Ice the solid, Water the liquid, and Steam the gas, are three

states of one natural object ; the condition of each state
being a certain amount of Heat 69

45. " The Phenomena of Heat are the Effects of a rapid Motion

of the Particles of Matter 63

46. " The Structure of Water 65

4,1' " Suppositions or Hypotheses ; their Uses and their Value. 67
43. " The Hypothesis that Water is composed of Separate Parti-
cles (Molecules) 68

49. " All Matter is probably made up either of Molecules or of

Atoms 70

50. " Elementary Bodies are neither destroyed nor is their Quan-

tity increased in Nature ^%

51. " Simple Mixture 73

52. " Mixture followed by Increase of Density ; Alcohol and

Water . , 74

53. ■" Solution ; Water Dissolves Salt 76

54- " Quicklime and Water : Plaster of Paris and Water : Com-
bination 79

55. " Mineral bodies may take on definite shapes and grow.or

increase in size, by the addition of like parts . . 8a
(B.) LIVING BODIES.

56. " The Wheat Plant and the substances of which it is com-

posed * 83

57. " The common Fowl and the Substances of which it is com-

posed 85

58. " Certain Constituents of the Body are very similar in the

Wheat Plant and in the Fowl 86

59. " Proteid Substances are met with in Nature only in Animals

and Plants; and Animals and Plants always contain Pro-

teids 87

ixi. " What is meant by the word Living? 88

61. " The Living Plant increases in Size, by adding to the Sub-

stances which compose its Body, like Substances; these,
however, are not derived from without, but are manu-
factured within the Body of the Plant from simpler Ma-
terials 88

62. " The Living Plant, after it has grown up, detaches i)art of

its Substance, which has the Power of developing into a
similar Plant, as a Seed 90

63. " The Living Animal increases in Size by adding to the Sub-

stances which compose its Body, likeSubstances; these,
however, are chiefly derived directly from other Animals
or from Plants 90

64. " The living Animal, after it has grown up, detaches part of

its Substance, which has the Power of growing into a
similar Animal, as an Ef^g 91

65. " Living Bodies differ from Mmeral Bodies in their Essential

Composition, in the manner of their Growth, and in the
fact that they are reproduced by Germs . . .91
III. IMMATERIAL OBJECTS.

66. " Mental Phenomena 9a

t7. " The order of Mental Phenomena: Psychology . . 94

SCIENCE PRIMERS,

INTRODUCTORY,

I. NATURE AND SOIENOE,

1. Sensations and Things.

All the time that we are awake we are learning by
means of our senses something about the world in
which we live and of which we form a part; we are
constantly aware of feeling, or hearing, or smelling,
and, unless we happen to be in the dark, of seeing; at
intervals we taste. We call the information thus
obtained sensation.

When we have any of these sensations we com-
monly say that we feel, or hear, or smell, or see, or
taste, something. A certain scent makes us say we
smell onions; a certain flavour, that we taste apples;
a certain sound, that we hear a carriage; a certain
appearance before our eyes, that we see a tree; and
we call that which we thus perceive by the aid of
our senses a thing or an object.

2. Causes and Effects.

Moreover, we say of all these things, or objects, that
^hey are the causes of the sensations in question, and

0 SCIENCE PRIMERS. [nature and

that the sensations are the effects of these causes.
For example, if we hear a certain sound, we say it is
caused by a carriage going along the road, or that it
is the effect, or the consequence, of a carriage passing
along. If there is a strong smell of burning, we believe
it to be the effect of something on fire, and look about
anxiously for the cause of the smell. If we see a tree,
we believe that there is a thing or object, which is the
cause of that appearance in our field of view.

3. The reason Why. Explanation.

In the case of the smell of burning, when we find
on looking about, that something actually is on fire,
we say indifferently either that we have found out the
cause of the smell, or that we know the reason why
we perceive that smell; or that we have explained
it. So that to know the reason why of anything, or to
explain it, is to know the cause of it. But that which
is the cause of one thing is the effect of another.
Thus, suppose we find some smouldering straw to be
the cause of the smell of burning, we immediately ask
what set it on fire, or what is the cause of its burning?
Perhaps we find that a lighted lucifer match has been
thrown into the straw, and then we say that the lighted
match was the cause of the fire. But a lucifer match
would not be in that place unless some person had
put it there. That is to say, the presence of the
lucifer match is an effect produced by somebody as
cause. So we ask why did any one put the match
there? Was it done carelessly, or did the person who
put it there intend to do so? And if so, what was
his motive, or the cause which led him to do such a
thing? An4 what was the reason for his having such

SCIENCE.] INTRODUCTORY

a motive ? It is plain that there is no end to the
questions, one arising out of the other, that might be
asked in this fashion.

Thus we believe that everything is the effect of
something which preceded it as its cause, and that
this cause is the effect of something else, and so on,
through a chain of causes and effects which goes back
as far as we choose to follow it. Anything is said to
be explained as soon as we have discovered its cause,
or the reason why it exists ; the explanation is fuller,
if we can find out the cause of that cause ; and the
further we can trace the chain of causes and effects,
the more satisfactory is the explanation. But no
explanation of anything can be complete, because
human knowledge, at its best, goes but a very little
way back towards the beginning of things.

4. Properties and Powers.

When a thing is found always to cause a particular
effect, we call that effect sometimes a property,
sometimes a power of the thing. Thus the odo.-
of onions is said to be a property of onions, because
onions always cause that particular sensation of
smell to arise, when they are brought near the
nose ; lead is said to have the property of heaviness,
because it always causes us to have the feeling ol
weight when we handle it ; a stream is said to have
the power to turn a waterwheel, because it causes the
waterwheel to turn ; and a venomous snake is said to
have the power to kill a man, because its bite may
cause a man to die. Properties and powers, then, are
certain effects caused by the things which are said to
possess them.

8 SCIENCE PRIMERS. [naturk and

5. Artificial and Natural Objects. Nature.

A great many of the things brought to our
knowledge by our senses, such as houses and furniture,
carriages and machines, are termed artificial things
or objects, because they have been shaped by the
art of man ; indeed, they are generally said to be
made by man. But a far greater number of things
owe nothing to the hand of man, and would be just
what they are if mankind did not exist, — such as the
sky and the clouds ; the sun, moon and stars ; the sea
with its rocks and shingly or sandy shores ; the hills
and dales of the land ; and all wild plants and animals.
Things of this kind are termed natural objects, and
to the whole of them we give the name of Nature.

6. Artificial Things are only Natural Things
shaped and brought together or separated by
Men.

Although this distinction between nature and art,
between natural and artificial things, is very easily
made and very convenient, it is needful to remember
that, in the long run, we owe everything to nature ;
that even those artificial objects which we commonly
say are made by men, are only natural objects shaped
and moved by men ; and that,in the sense of creating,
that is to say, of causing something to exist which
did not exist in some other shape before, man can
make nothing whatever. Moreover, we must recollect
that what men do in the way of shaping and bringing
together or separating natural objects, is done in virtue
of the powers which they themselves possess ^5 natural
objects.

SCIENCE.] IN-TRODUCTORY, 9

Artificial things are, in fact, all produced by the
action of that part of nature which we call mankind,
upon the rest.

We talk of "" making" a box, and rightly enough, if
we mean only that we have shaped the pieces of wood
and nailed them together; but the wood is a natural
object and so is the iron of the nails. A watch is
"made" of the natural objects gold and other metals,
sand, soda, rubies, brought together, and shaped in
various ways; a coat is "made" of the natural object,
wool; and a frock of the natural objects, cotton or
silk. Moreover, the men who make all these things
are natural objects.

Carpenters, builders, shoemakers, and all other
artisans and artists, are persons who have learned so
much of the powers and properties of certain natural
objects, and of the chain of causes and effects in
nature, as enables them to shape and put together those
natural objects, so as to make them useful to man.

A carpenter could not, as we say, "make" a chair
unless he knew something of the properties and
powers of wood; a blacksmith fould not "make" a
horseshoe unless he knew that it is a property of iron
to become soft and easily hammered into shape when
it is made red-hot; a brickmaker must know many of
the properties of clay; and a plumber could not do
his work unless he knew that lead has the properties
of softness and flexibility, and that a moderate heat
uises it to melt.

So that the practice of every art implies a certain
knowledge of natural causes and effects; and the
improvement of the arts depends upon our learning
more and more of the properties and powers of natural

lo SCIENCE PRIMERS. [nature and

objects, and discovering how to turn the properties
and the powers of things and the connections of cause
and effect among them to our own advantage.

7. Many Objects and Chains of Causes and
Effects in Nature are out of our reach.

Among natural objects, as we have seen, there
are some that we can get hold of and turn to
account. But all the greatest things in nature and the
links of cause and effect which connect them, are
utterly beyond our reach. The sun rises and sets;
the moon and the stars move through the sky; fine
weather and storms, cold and heat, alternate. The
sea changes from violent disturbance to glassy calm,
as the winds sweep over it with varying strength or
die away; innumerable plants and animals come in
being and vanish again, without our being able to exert
the slightest influence on the majestic procession of
the series of great natural events. Hurricanes ravage
one spot; earthquakes destroy another; volcanic erup-
tions lay waste a third. A fine season scatters wealth
and abundance here, and a long drought brings
pestilence and famine there. In all such cases, the
direct influence of man avails him nothing; and, so
long as he is ignorant, he is the mere sport of the
greater powers of nature.

8. The Order of Nature : nothing happens
by Accident, and there is no such thing as
Chance.

But the first thing that men learned, as soon as
they began to study nature carefully, was that some
eY?nt§ take place in regular orderan^ that some causes

SCIENCE. ] IN TROD UCTOR Y. 1 1

always give rise to the same effects. The sun always
rises on one side and sets on the other side of the
sky; the changes of the moon follow one another in
the same order and with similar intervals; some stars
never sink below the horizon of the place in which
we live; the seasons are more or less regular; water
always flows down-hill; fire always burns; plants
grow up from seed and yield seed, from which like
plants grow up again; animals are born, grow, reach
maturity, and die, age after age, in the same way.
Thus the notion of an order of nature and of a
fixity in the relation of cause and effect between
things gradually entered the minds of men. So far
as such order prevailed it was felt that things were
explained; while the things that could not be ex-
plained were said to have come about by chance, or
to happen by accident.

But the more carefully nature has been studied, the
more widely has order been found to prevail, while
what seemed disorder has proved to be nothing but
complexity; until, at present, no one is so foolish as
to believe that anything happens by chance, or that
there are any real accidents, in the sense of events
which have no cause And if we say that a thing
happens by chance, everybody admits that all we
really mean is, that we do not know its cause or
the reason why that particular thing happens. Chance
and accident are only aliases of ignorance.

At this present moment, as I look out of my window,
it is raining and blowing hard, and the branches of the
trees are waving wildly to and fro. It may be that a
man has taken shelter under one of these trees ; perhaps,
if a stronger gust than usual comes, abranch will l)r^^kj

12 SCIENCE PRIMERS, [nature and

fall upon the man, and seriously hurt him. If that
happens it will be called an " accident," and the man
will perhaps say that by " chance" he went out, and
then "chanced" to take refuge under the tree, and so
the " accident" happened. But there is neither chance
nor accident in the matter. The storm is the effect of
causes operating upon the atmosphere, perhaps hun-
dreds of miles away; every vibration of a leaf is the
consequence of the mechanical force of the wind
acting on the surface exposed to it; if the bough
breaks, it will do so in consequence of the relation
between its strength and the force of the wind; if it
falls upon the man it will do so in consequence of the
action of other definite natural causes; and the posi-
tion of the man under it is only the last term in a
series of causes and effects, which have followed one
another in natural order, from that cause, the effect of
which was his setting out, to that the effect of which
was his stepping under the tree.

But, inasmuch as we are not wise enough to be able
to unravel all these long and complicated series of
causes and effects which lead to the falling of the
branch upon the man, we call such an event an
accident.

9. Laws of Nature ; Laws are not Causes.

When we have made out by careful and repeated
observation that something is always the cause of a
certain effect, or that certain events always take place
in the same order, we speak of the truth thus dis-
covered as a law of Nature. Thus it is a law of
p^ture that anything heavy falls to the ground if iti§

SCIENCE.] Il^TRObUCTOkV. \%

unsupported; it is a law of nature that, under or-
dinary conditions, lead is soft and heavy, while flint
is hard and brittle; because experience shows us that
heavy things always do fall if they are unsupported,
that, under ordinary conditions, lead is always soft
and that flint is always hard.

In fact, everything that we know about the powers
and properties of natural objects and about the order
of nature may properly be termed a law of nature.
But it is desirable to remember that which is very
often forgotten, that the laws of nature are not the
causes of the order of nature, but only our way of
stating as much as we have made out of that order.
Stones do not fall to the ground in consequence of
the law just stated, as people sometimes carelessly
say; but the law is a way of asserting that which in-
variably happens when heavy bodies at the surface of
the earth, stones among the rest, are free to move.

The laws of nature are, in fact, in this respect, similar
to the laws which men make for the guidance of their
conduct towards one another. There are laws about
the payment of taxes, and there are laws against
stealing or murder. But the law is not the cause of a
man's paying his taxes, nor is it the cause of his
abstaining from theft and murder. The law is simply
a statement of what will happen to a man if he does
not pay his taxes, and if he commits theft or murder;
and the cause of his paying his taxes, or abstaining
from crime (in the absence of any better motive) is the
fear of consequences which is the effect of his belief

that statement. A law of man tells what we may
expect society will do under certain circumstances;
and a law of nature tells us what we may expect

14 SCIENCE Primers. [natijre km

natural objects will do under certain circumstances.
Each contains information addressed to our intelli-
gence, and except so far as it influences our intelli-
gence, it is merely so much sound or writing.

While there is this much analogy between human
and natural laws, however, certain essential differences
between the two must not be overlooked. Human
law consists of commands addressed to voluntary
agents, which they may obey or disobey; and the
law is not rendered null and void by being broken.
Natural laws, on the other hand, are not commands
but assertions respecting the invariable order of
nature; and they remain laws only so long as they
can be shown to express that order. To speak of the
violation, or the suspension, of a law of nature is an
absurdity. All that the phrase can really mean is
that, under certain circumstances the assertion con-
tained in the law is not true; and the just conclusion
is, not that the order of nature is interrupted, but
that we have made a mistake in stating that order.
A true natural law is an universal rule, and, as such,
admits of no exceptions.

Again, human laws have no meaning apart from the
existence of human society. Natural laws express the
general course of nature, of which human society
forms only an insignificant fraction.

lo. Knowledge of Nature is the Guide of
Practical Conduct

If nothing happens by chance, but everything in
nature follows a definite order, and if the laws of
nature embody that which we have been able to learn

SCIENCE.] tNTRODUCTORV. \%

about the order of nature in accurate language, then
it becomes very important for us to know as many as
we can of these laws of nature, in order that we may
guide our conduct by tliem.

Any man who should attempt to live in a country
without reference to the laws of that country would
very soon find himself in trouble; and if he were
fined, imprisoned, or even hanged, sensible people
would probably consider that he had earned his fate
by his folly.

In like manner, any one who tries to live upon the
face of this earth without attention to the laws of
nature will live there for but a very short time, most
of which will be passed in exceeding discomfort; a
peculiarity of natural laws, as distinguished from those
of human enactment, being that they take effect
without summons or prosecution. In fact, nobody
could live for half a day unless he attended to some
of the laws of nature; and thousands of us are dying
daily, or living miserably, because men have not yet
been sufficiently zealous to learn the code of nature.

It has already been seen that the practice of all
our arts and industries depends upon our knowing
the properties of natural objects which we can get
hold of and put together; and though we may be
able to exert no direct control over the greater
natural objects and the general succession of causes
and effects in nature, yet, if we know the properties
and powers of these objects, and the customary order
of events, we may elude that which is injurious to us,
and profit by that which is favourable.

Thus, though men can nowise alter the seasons or
change the process of growth in plants, yet having

l6 SCIENCE PRIMERS. [natuhkand

learned the ofder of nature in these matters, they
make arrangements for sowing and reaping accord-
ingly; they cannot make the wind blow, but when it
does blow they take advantage of its known powers
and probable direction to sail ships and turn wind-
mills; they cannot arrest the lightning, but they can
make it harmless by means of conductors, the con-
struction of which implies a knowledge of some of the
laws of that electricity, of which lightning is one of
the manifestations. Forewarned is forearmed, says
the proverb; and knowledge of the laws of nature is
forewarning of that which we may expect to happen,
when we have to deal with natural objects.

II. Science: the Knowledge of the Laws
of Nature obtained by Observation, Experi-
ment, and Reasoning.

No line can be drawn between common knowledge
of things and scientific knowledge; nor between com-
mon reasoning and scientific reasoning. In strictness
all accurate knowledge is Science ; and all exact
reasoning is scientific reasoning. The method of
observation and experiment by which such great
results are obtained in science, is identically the same
as that which is employed by every one, every day of
his life, but refined and rendered precise. If a child
acquires a new toy, he observes its character and ex-
periments upon its properties; and we are all of us
constantly making observations and experiments upon
one thing or another.

But those who have never tried to observe accu-
rately will be surprised to find how diffcult a business
it is. There is not one person in a hundred who can

SCIENCE. ] IN TROD UCTOR V. 17

describe the commonest occurrence with even an ap-
proach to accuracy. That is to say, either he will
omit something which did occur, and which is of im-
portance; or he will imply or suggest the occurrence
of something which he did not actually observe, but
which he unconsciously infers must have happened.
When two truthful witnesses contradict one another
in a court of justice, it usually turns out that one or
other, or sometimes both, are confounding their in-
ferences from what they saw with that which they
actually saw. A swears that B picked his pocket.
It turns out that all that A really knows is that he
felt a hand in his pocket when B was close to him ;
and that B was not the thief, but C, whom A did not
observe. Untrained observers mix up together their
inferences from what they see with that which they
actually see in the most wonderful way; and even
experienced and careful observers are in constant
danger of falling into the same error.

Scientific observation is such as is at once full,
precise, and free from unconscious inference.

Experiment is the observation of that which hap-
j.cns when we intentionally bring natural objects
together, or separate them, or in any way change
the conditions under which they are placed. Scien-
tific experiment, therefore, is scientific observation per-
' Tmed under accurately known artificial conditions.

It is a matter of common observation that water
• metimes freezes. The observation becomes scien-
v.iic when we ascertain under what exact conditions
the change of water into ice takes place. The com-
monest experiments tell us that wood floats in water.

l8 SCIENCE PRIMERS. [nature and

Scientific experiment shows that, in floating, it dis-
places its own weight of the water.

Scientific reasoning differs from ordinary reason-
ing in just the same way as scientific observation and
experiment differ from ordinary observation and ex-
periment— that is to say, it strives to be accurate;
and it is just as hard to reason accurately as it is to
observe accurately.

In scientific reasoning general rules are collected
from the observation of many particular cases; and,
when these general rules are established, conclusions
are deduced from them, just as in every-day life. If
a boy says that " marbles are hard," he has drawn
a conclusion as to marbles in general from the
marbles he happens to have seen and felt, and has
reasoned in that mode which is technically termed
induction. If he declines to try to break a marble
with his teeth, it is because he consciously, or un-
consciously, performs the converse operation of de-
duction from the general rule " marbles are too hard
to break with one's teeth."

You will learn more about the process of reasoning
when youstudy Logic, which treatsof that subject in
full. At present, it is sufficient to know that the laws
of nature are the general rules respecting the be-
haviour cf natural objects, which have been collected
from innumerable observations and experiments; or, in
other words, that they are inductions from those
observation^ and experiments. The practical and
theoretical results of science are the products
of deductive reasoning from these general rules.

Thus science and common sense are not opposed,
as people sometimes fancy them to be, but science is

sciENCK.] INTRODUCTORY. 19

perfected common sense. Scientific reasoning is
simply very careful common reasoning, and common
knowledge grows into scientific knowledge as it be-
comes more and more exact and complete.

The way to science then lies through common knowl-
edge; we must extend that knowledge by careful ob-
servation and experiment, and learn how to state the
results of our investigations accurately, in general
rules or laws of nature; finally, we must learn how
to reason accurately from these rules, and thus arrive
at rational explanations of natural phenomena, which
may suffice for our guidance in life.

n. MATERIAL OBJECTS.— A. MINERAL BODIES.

12. The Natural Object Water.

One of the commonest of common natural objects
water; everybody uses it in one way or another
^very day; and consequently everybody possesses a
store of loose information — of common knowledge —
about it. But, in all probability, a great deal of this
knowledge has never been attended to by its pos-
sessor; and certainly, those who have never tried to
learn how much may be known about water, will be
ignorant of a great many of its powers and properties
and of the laws of nature which it illustrates; and
consequently will be unable to account for many
things of which the explanation is very easy. So
we may as well make a beginning of science by
$tudyin<i water.

20 SCIENCE PRIMERS. [materia>

13. A Tumbler of Water.

Suppose we have a tumbler half-full of water. The
tumbler is an artificial object (§ 5); that is to say,
certain natural objects have been brought together
and heated till they melted into glass, and this glass
has been shaped by a workman. The water, on the
other hand, is a natural object, which has come from
some river, pond, or spring; or it may be from a
water-butt into which the rain which has fallen on
the roof of a house has flowed.

Now the water has a vast number of peculiarities.
For example, it is transparent, so that you can see
through it; it feels cool; it will quench thirst and dis-
solve sugar. But these are not the characters which
it is most convenient to begin with.

14. Water occupies Space; it offers Resist-
ance; it has Weight; and is able to transfer
Motion which it has acquired; it is therefore
a form of Matter.

The water, we see, fills the cavity of the tumbler
for half its height, therefore it occupies that much
space, or has that bulk or volume. If you put the
closed end of another tumbler of almost the same size
into the first, you will find that when it reaches the
water, the latter offers a resistance to its going down,
and unless some of the water can get out, the end of
the second tumbler will not go in. Any one who falls
from a height into water will find that he receives a
severe shock when he reaches it. Water therefore
offers resistance.

if the water is emptied out, the tumbler feels much

objects] introductory. 21

lighter than it was before ; water, therefore, has
weight.

And, finally, if you throw the water out of the tum-
bler at any slightly supported object, the water hitting
against it would knock it over. That is to say, the
water being put in motion is able to transfer that
motion to something else.

All these phenomena, as things which happen in
nature are often called, are effects of which water,
under the conditions mentioned, is the cause, and they
may therefore be said to be properties (§ 4) of water.
All things which occupy space, offer resistance,
possess weight and transfer motion to other things
when they strike against them, are termed material
substances or bodies, or simply matter. Water,
therefore, is a kind, or form, of matter.
15 Water is a liquid.

You will easily observe that, though water occupies
space, it has no definite shape, but fits itself exactly
to the figure of the vessel which holds it. If the
tumbler is cylmdrical, the contour of the surface of
the water will be circular when the tumbler is held
vertically, and will change, without the least break or
interruption, to more and more of an oval when the tum-
bler is inclined, and whatever the shape of the vessel
into which you pout it, the sides of the water always
exactly fit against the sides of the vessel. If you put
l^^vour finger into the water you can move it in all direc-
^^^Kons with scarcely any feeling of obstacle. If you
^^Bull your finger out there is no hole left, the water on
^^Bl sides rushing together to fill up the space that was
^^pccupied by the finger. You cannot take up a handful of

22 SCIENCE PRIMERS. [material

water, for it runs away between your fingers, and you
cannot raise it into a permanent heap. All this shows
that the parts of water move upon one another with
great ease. The same fact is illustrated if the tumbler
is inclined so that the level of the surface rises above
the edge of the tumbler on one side, and the water
is therefore to some extent unsupported by the tumbler
at this point. The water then flows over in a stream
and falls to the ground, where it spreads out and runs
to the lowest accessible place, or gradually soaks up
into crevices.

Nevertheless, although the parts of the water thus
loosely slip and slide upon one another, yet they hold
together to a certain extent. If the surface of the
water is just touched with the finger, a little of it will
adhere; and if the finger is then slowly and carefully
raised, the adjacent water will be raised up into a
slender column which acquires a noticeable length
before it breaks. So, in the early morning, after heavy
dew, you may see the water upon cabbage-leaves and
blades of grass in spherical drops, the parts of which
similarly hold together.

Material substances, the parts of which are so
movable that they fit themselves exactly to the sides
of any vessel which contains them, and which flow
when they are not supported, are called fluids, and
fluids the parts of which do not fly off from one
another, but hold together as those of water do, are
called liquids.

Water therefore is a liquid.

i6. Water is almost incompressible.

It has been seen that water, like every other

OBJECTS.] mTRODVCTORY, 23

material substance, resists the intrusion of other mat-
ter into the place which it occupies. But many things,
though they resist, can be easily squeezed or com-
pressed into a smaller volume. This, however, is not
the case with water, which like other liquids, is almost
incompressible; that is to say, an immense pres-
sure is needful to cause its volume to diminish to any
appreciable extent. It may seem strange that anything
so apparently yielding as w^ter should yet be almost
as difficult to squeeze as so much iron ; but the apparent
yieldingness of water is due to the ease with which
it changes its shape; and, if water is prevented from
changing its shape, it is very difficult to drive its parts
closer together. It has been ascertained that if water
is confined in a closed space, a pressure amounting to
fifteen pounds on the square inch diminishes its volume
by only ^Tj^xrTjth part. Take a common syringe, and
having seen that the plug or piston fits the cylinder
of the syringe well, put the nozzle into water and draw
the piston up. Then turn the nozzle upward and
push upon the piston till a little of the water squirts
out, so as to make sure that the cylinder contains
nothing but water. Now put your finger on the
opening of the nozzle firmly, so as to stop any water
from passing out, and then try to push the piston down.
You will find that you cannot make it stir without great
force; and, if the piston moves appreciably, it will be
because some of the water has escaped by the sides
of the piston. In fact, if the piston presented a square
inch of surface, and fitted accurately, and the column
of water in the cylinder were one inch long, it must
be pressed down by a weight of 30,000 pounds (about
thirteen tons) to make it move one-tenth of an inch.

24 SCIENCE PRIMERS. [MAtERiAt

17. The Meaning of Weight.

Let us next consider the property of weight. We
say that anything has weight when, on trying to lift it
from the ground, or on holding it in the hand, we have
a feeling of effort. Or again, if anything which is sup-
ported at a certain height above the ground, falls when
the support is taken away, we say that it has weight.
Now the ground merely means the surface of the earth ;
and, as all bodies which possess weight fall directly to-
wards the surface of the earth when they are not kept
away from it by some support, we may say that all
bodies which have weight tend to fall in this way. And
it does not matter on what part of the surface of the
earth you make the experiment. Rain consists of
drops of water, and it does not matter whether we
watch a shower in calm weather here, or in New
Zealand; the drops fall perpendicularly towards the
ground. But we know that the earth is a globe, and
that New Zealand is at our antipodes, or on the
opposite side of the globe to England. Hence if
two showers are falling at the same time, one in New
Zealand and one here^ — the drops must be falling in
opposite directions, towards one another; that is,
towards the centre of the earth which lies between
them. In fact, all bodies which have weight tend to
fall towards the centre of the earth — that is to say
they fall in this way if there is nothing to prevent
them: and when we speak of weight we mean this
tendency to fall. To call anything heavy, is the
same as saying that we fully expect that, if there is
nothing to support it, it will fall to the ground; or
that if we support it ourselves we shall be conscious
of effort.

^

objEcts.l WTkODVCTOkY. »^

1 8. Gravity and Gravitation.

The word gravity, when it was first used, had ex-
actly the same meaning as weight; and a body which
has weight is said to gravitate towards the center of
the earth. But gravity has now acquired a much
wider sense than weight. For an immense number
of careful observations and experiments have estab-
lished the general rule, or law of nature, that every
material substance, tends to approach every other
material substance, just in the same way as a drop of
rain falls towards the earth; and, in fact, that any
two portions of matter, whatever the nature of that
matter may be, will move towards one another if there
is nothing to prevent them from doing so.

To make this clear, let us suppose that the only
material bodies in the universe were two spherical drops
of water, each a tenth of an inch in diameter. Each
of these drops would have the same bulk as the other,
and would be a quantity of matter exactly equivalent
to the other. Then, however great the distance
which separated these two drops, they would begin
to approach one another; and, each moving with
gradually increasing swiftness, they would at length
meet in a point exactly half-way between the positions
which they at first occupied. But if the bulk
of one drop were greater than that of the other
drop, then the larger would move more slowly, and
the point of meeting would be by so much nearer
the larger drop. It follows that, if the one body of
water were as big as the earth and the other remained
of its original size, no bigger than a rain-drop — the
motion of the large mass towards the small one would
be an inconceivably minute fraction of the total

26 SCIENCE: PRiMEkS. [MAtEklAl,

distance travelled over. It would appear as if the
large body were perfectly still and drew the small body
to itself.

This is just what happens when a single drop of
water falls from a cloud, say through a distance
of a mile, to the earth. The earth really moves
towards it, just as it moves towards the earth, on
the straight line which joins the centres of the two,
But the length of this line which eaoh travels over
is inversely proportional to the quantity of matter
in each, that is to say is the less the big^ger the quan-
tity. So that we have a rule-of-three sum. As the
quantity of matter in the earth is to that in a rain-
drop, so is a mile to the distance travelled over by
the earth. And if any one worked out this sum, he
would find that the fourth term of the proportion
would be an inconceivably minute fraction of an
inch. For all practical purposes, therefore, we may
consider the earth to be at rest in relation to all
falling bodies, inasmuch as the quantity of matter in
any falling body is insignificant, in comparison with
that contained in the earth.

What is true of water is true, so far as we know, of
all kinds of matter, and we therefore say that it is a
law of nature that all kinds of matter possess gravity;
that is to say, that of any two, each tends to move
towards the other, at a speed which is the slower the
gaeater the quantity of matter it contains in propor-
tion to that which the other contains; and this speed
gradually becomes quicker as the two bodies approach.

What is usually called the law of gravitation is
a statement of the same observed facts in another and
more complete fashion. (See Physics Primer^

OBJECTS.] INTkODUCTOkV. 27

19. The cause of Weight: Attraction:
Force.

We know nothing whatever of the reason why
bodies possess weight. Bodies do not fall on account
of the law of gravitation (§ 9;; nor does their gravity-
explain why they fall. Gravity, as we have seen, is
only a name for weight, and the law of gravitation is
only a statement of how bodies approach one another,
not why they do so.

It is often said that gravitation is attraction, and
that bodies fall to the earth because the earth attracts
them. But the word " attract" simply means to " draw
towards," and " attraction" means nothing but ** draw-
ing towards;" and to say, when two bodies move to-
wards one another, that they are " drawn towards" one
another, is simply to describe the fact and makes us
no whit wiser than we were before. On the contrary,
unless we take great care, it may make us a little less
wise. For the words " drawing towards" are so closely
associated with ropes and hooks and the act of pulling,
that we are easily led to fancy the existence of some
analogous invisible machinery in the case of mutually
attractive bodies.

Again, gravitation is spoken of as a force; and
as the word force is in very common use, let us try to
make out what we mean by it. A man is said to exert
force when he pushes or pulls anything so as either to
exert pressure upon it or to put it in motion, A
wrestler's force is proved by his hug; a bowler's force
is shown by the swiftness of motion of the ball.

Force, then, is the name which we give to that
which causes or, in the case of pressure, tends to
cause, motion. The force of gravity therefore means

2S ^C/El^CE PRIMERS. [material

the cause of the pressure which we feel when bodies
which possess gravity are supported by our bodies,
and the cause of their movement towards the centre
of the earth, when they are free to move. But it is
exactly about the cause of these phenomena that we
know nothing whatever.

A good deal of mischief is done by the inaccurate use
of such words as attraction and force, as if they were
the names of things having an existence apart from
natural objects, and from the series of causes and effects
which are open to our observation; while they are, in
reality, merely the names of the unknown causes of
certain phenomena. And it is worth while to take
pains to get clear ideas on this head at the outset of
the study of science.

Let us remember then that, so far as we know, it is
a law of nature, that any two material bodies, if they
are free to move, approach one another with grad-
ually increasing swiftness; and that the space over
which each travels before the two meet, is inversely pro-
portional to the quantity of matter which it contains.
Attraction of gravitation is a name for this gene-
ral fact; weight is the name for the fact in the case
of terrestrial bodies; force is a name which we give
to the unknown cause of the fact. The fact is that
which it is important to know. The names are of no
great consequence so long as we recollect that they
are merely names and not things.

20. The Weight of Water is Proportioned
to its Bulk.

We must next consider, not weight in general, but
the weight of water. We say that a tumbler full of

OBJECTS.] INTRODUCTORY. 29

water is heavier than an empty tumbler, because the
full tumbler gives us a greater feeling of effort when
we lift it than the empty tumbler does. The more
water there is in the tumbler the greater is the effort.
A pail full of water requires still more effort, though
the empty pail feels quite light; and, when we come to
deal with a large tub full of water, we may be unable
to stir it, though the empty tub could be lifted with
case. Thus it seems that the greater the bulk of
water the more it v/eighs, and the less the bulk the
less it weighs. But then a single drop of water in the
palm of the hand seems to weigh nothing at all.
However, this clearly cannot be, for the drop falls to
the ground readily, and therefore it must have weight.
Moreover, a few thousand drops would fill the tumbler,
and if a thousand drops weigh something, each drop
must have a thousandth of that weight. The fact is
that our feeling of effort is a very rough measure of
weight, and does not enable us to compare small
weights, or even to perceive them if they are very
small. To know anything accurately about weight
we must have recourse to an instrument which is
contrived for the purpose of measuring weights with
precision.

21. The Measuring of Weights. The
Balance.

Such an instrument is the balance or scales, which
you may see in every grocer's shop. It is composed
of a beam which moves easily on a pivot fixed to its
middle, and which has a scale-pan attached to each
end. So long as both scale-pans are empty the beam
is horizontal; but if you put anA'thing which has

30 SCIENCE PRIMERS. [material

weight into one, that one goes down and the other
rises. If now you either pull or push the empty
scale downwards, the beam may be brought into the
horizontal position again, and the effort required to
bring it into the horizontal position will be the
greater, the greater the weight of the body in the
opposite scale. An ounce in the one scale is easily
raised by the pressure of a finger in the other. A
pound requires more effort; ten pounds needs put-
ting out the strength of the arm; to raise fifty pounds
involves still more exertion ; while a couple of hundred-
weight will not be stirred by the strongest push or pull
upon the empty scale.

Suppose that, instead of pressing down the empty
scale, you put something that has weight into it;
then, as soon as this weight is equal to that in the
other scale, the beam will become horizontal. In fact,
one scale has just as much tendency to move towards
the centre of the earth as the other has, and as neither
can go down without pulling the other up, they neu-
tralise one another. It comes to the same thing, as if
two boys of equal strength were pulling one against
the other; so long as the pulls in opposite directions
are equal, of course neither boy can stir; while the
smallest addition of strength to one enables him to
pull the other over.

22. The Weight of the same Bulk or
Volume of Water is Constant under the same
conditions. Mass. Density.

Now let two graduated thin glass measures be put
into the two scales, and made to counterpoise one
another exactly. Then, if even a single drop of

OBJECTS.] INTRODUCTORY. 31

water is put into the one measure the scale will
descend, if the balance is a good one ; sho\^ng that
the drop has weight. If the measures are graduated
accurately, then whatever volume of water is put into
one, an exactly similar volume of the same water must
be put into the other to make the beam level. This
obviously means that the same volume of water
under the same circumstances always has
the same weight.

In § 18 it was said that bodies tend to move to-
wards one another with a relative velocity' which is
inversely proportional to the quantity of matter which
they contain. But how are we to measure quantity of
matter? Is it to be estimated by the space which it
occupies ; that is, by its volume ? or are we to esti-
mate the quantity of matter in a body by its weight ?
You will soon learn that the volume of all bodies
is constantly changing in correspondence with the
changes in the pressure exerted by other bodies, but
more especially in correspondence with the changes
of temperature to which they are subjected ; while
the weight of the same body, at the same point on
the earth's surface, never alters. Hence we may
take the weight of a body as a measure of the quantity
of matter which it contains ; and it follows that, for the
same weight, the larger the volume of a body the less
matter it contains proportionally to its volume, and
the less the volume, the more matter it contains. The

' Velocity, or swiftness, is measured by the distance over which
a body travels, in a given time. Of two bodies, one of which
travels through one foot m a second, while the other travels
through two feet, the latter has the greater relative velocity.

32 SCIENCE PRIMERS. [material

proportion of its weight to its volume gives us the
densitjfeof a body.

Now what is true of water is true of all other bodies
or material substances. Suppose that one of tlie
measures is emptied and replaced, the beam may be
brought to the horizontal position again by means of
a piece of lead cut to exactly the right size. The
piece of lead will thenceforth furnish an exactly cor-
responding or equivalent weight for so much water ;
and pieces of iron or brass, which counterpoise the
lead, will also be equivalents of the weight of the water,
or of the lead, or of one another. But the pieces of
lead, iron, or brass will obviously be of much less
volume or bulk than the water which they counterpoise.
Here it follows that the densities of these metals, or
the quantity of matter contained in the same volume,
must be much greater than in the case of water.

What are called weights in commerce are pieces of
lead, or iron, or brass exactly equivalent in weight to a
certain bulk of water under certain conditions. An
imperial gallon of water thus weighs ten
pounds, and therefore an imperial pint
weighs a pound and a quarter.

23. Equal Volumes of Different Things
under the same circumstances, have Different
Weights : the Density of Different Bodies is
Different.

The important fact which has just been alluded to
must be considered more fully. We have seen that
an imperial pint measure gives us the space which is
taken up by as much water as weighs a pound and a
quarter; and this space is the bulk or volume of that

OBJECTS.] INTRODUCTORY. 33

weight of water. But if you take an ordinary pound

weight and a quarter-pound weight, and put them into

ail imperial pint measure, you will find that instead of

filling it, they take up only a very small portion of the

space in its interior, or in other words, of its capacity.

Thus the volume of a pound and a quarter of lead, or

o* iron, or of brass, is very much less than the volume

of t'l*^ same weight of water; that is to say, the metals

are d^enser than water; the same volume has greater

mass or more gravity. Or, to put the case in another

way, till the tumbler with which we began half full of

water, making a mark on the side exactly at the level

of the top of the water. Then place it in one scale of a

balance, and counterpoise it with weights in the other.

Next, pour out the water, and after drying the

tumbler, fill it with fine sand carefully up to the mark.

The volume of sand will be equal to the volume of

water But now the same weights will no longer

ounterpoise it, and you will have to put more

weights in the opposite scale. Volume for volume,

therefore, sand is heavier than water. Throw out the

and, and put in sawdust in the same way, and you

• ill find that a less weight than was necessary to

ounterpoise the water counterpoises the sawdust.

\'olume for volume, therefore, sawdust is lighter than

water. Experiment in the same way with spirit and

il, and they will be found to be lighter than water,

-hile treacle will be heavier, and quicksilver very

iiuich heavier than water.

24. The Meaning of Heavy and Light —
Specific Gravity.

We are in the habit of using the words heavy and

34 SCIENCE PRIMERS. [material

light rather carelessly. We call things that are easily
lifted light, and things that are hard to lift heavy.
We say that sand, which is blown about by the wind,
is light, and that a block of wood is heavy, and yet
we have just seen that sand is heavier, bulk for
bulk, than wood. In order to get rid of this
double meaning, the weight of a volume of any
liquid or solid, in proportion to the weight of the
same volume of water at a known temperature and
pressure, is called its specific gravity. Water being
taken as i, anything a volume of which is twice as
heavy as the same volume of water is said to have
the specific gravity 2 ; if three times, 3 ; if four awd a
half times, 4*5, and so on. Thus the specific gravity
of any liquid or solid expresses its density in pro-
portion to that of water under the same conditions.
Sawdust, oil, and spirit have a less specific gravity than
water, while treacle, sand, and quicksilver have a
greater specific gravity. In this sense, the former
three substances are light, while the latter three are
heavy.

25. Things of greater Specific Gravity
than Water sink in Water; Things of less
Specific Gravity float.

Here are two tumblers of water. Throw some
sand into one and some sawdust into the other.
What happens? The sand sinks to the bottom, the
'sawdust floats at the top. We may stir them up as
we like, but the sand will tumble to the bottom and
the sawdust, as obstinately, rise to the top. Thus
that which is lighter than the water floats, and that
which is heavier (bulk for bulk) sinks. So, if we pour

OBJECTS.] INTRODUCTORY. %%

some oil into the water, it floats, and if we pour some
coloured spirit in carefully, it also floats; while treacle
and quicksilver sink to the bottom, just as the iron-
filings do.

We saw that the iron-filings sank, because iron is
heavier than water. Here is a piece of the thin tinned
sheet-iron that they make tin boxes of. What will
happen if we drop it into the water? It is heavier
than water, bulk for bulk, and therefore it will sink as
you see it does.

But now here is a '* tin" canister made of this very
same tinned sheet-iron. We drop that into the water,
and you see it does not sink at all, but floats at the
top as if it were made of cork. Here is a perplexity.
We were sure just now that iron is heavier than water,
and here is an iron box floating! Is this an exception
to the law? Not at all; for what we said was that a
thing would float if it were lighter, bulk for bulk,
than water. Now let us weigh the tin box, and having
weighed it let us next try to find out how much the
same bulk of water weighs. This may be done very
simply, for the walls of the box are very thin, so that
the inside of the box is very nearly as large as the
whole box. Consequently, if we fill the box with
water, and then weigh the water, we shall find out,
very nearly, what is the weight of a bulk of water as
great as that of the box. But if we do this, we shall
find that the water which was contained in the box,
eighs very much more than the box does. So that,
bulk for bulk, the box, although it is made of iron,
is really lighter than water, and that is why it floats.

You will all have heard of the iron ships which are
now so common, and you may have wondered how it

36 SCIENCE PRTMERS. [material

IS, that ships made of thick plates of iron riveted
together, and weighing many thousand tons, do not
go to the bottom. But they are nothing but our tin
canisters on a great scale, and they float because each
ship weighs less than a quantity of water of the same
bulk does.

It is because of this property of water to bear up
things lighter than itself, and because of that other
property of being easily moved which the particles of
water have, that the sea, and rivers, and canals, are
such great highways for mankind.

For there is nothing so heavy that it may not be
made to float in water, if the box which holds it is
large enough to make the weight of the whole less
than the weight of the same bulk of water. And
then, having once got the weight to float, the particles
of water are so easily moved, that the force of the
winds, or of oars, or of paddles, readily causes it to
slip through the water from one place to another.

26. A Body which Floats in Water always
occupies as much Space beneath the level of
the Surface of the Water as is equal to the
Volume of Water which weighs as much as
that Body ; in other words, it displaces its
own Weight of Water.

. A cubic inch of water weiglis about 252 grains and a
half. Suppose that the tin box in the previous experi-
ment was square, and had the bulk of 100 cubic inches,
then the weight of a corresponding volume of water
would be 25,250 grains. If the box weighed 8,416
grains^ just a third of its bulk-would be imi^ersed; if

unjKcTs.] INTIWD UCTOR K 3^

i2;625 grains, half ; if 16, 832 grains, it would sink two-
thirds of its volume, and so on. Or, if, when the box
is floating, you make a mark upon its side at the exact
level of the surface of the water, the bulk of that
portion of the box which lies below the water-level
can be ascertained. Suppose it to be thirty cubic
inches, then the weight of the box will be 30x252*5
or 7575 grains. Hence it may be said that the im-
mersed part of a floating body takes the place of the
water which it displaces, and, as it were, represents
it. If you press downwards upon the floating box,
there is a feeling of resistance as it descends, and
when the pressure is taken off, the body immediately
rises again. Hence the water presses upwards against
the bottom of the floating body. But it also presses
against the sides, for if the sides of the box are very
thin they will be driven in. If a thin empty bottle is
tightly corked and lowered into deep water tlie cork
will be driven in, or else the bottle will be crushed.

27. Water presses in all Directions.

Thus water presses in all directions upon things
which are immersed in it.

If a long wooden or metal pipe, placed vertically,
has its lower end stopped with a cork wliich does not
fit very tightly, and water is poured into the top of the
tube, the water will at first fill the part of the tube
above the cork, and its weight will exert a certain
pressure on the cork. In fact, if the end of the
tube is stopped by applying the palm of the hand
closely against it, the downward pressure of the
water will have to be overcome by a certain amount
of effort. As the water accumulates, this downward

38 SCIENCE PRIMERS, [matkrial

pressure will become greaier and greater until the
hand is driven away, or the cork is forced out, and the
water falls to the ground. The pressure in this case
is the same as the weight of the water, and the cork
would have been driven out equally well by a rod of
lead of the same weight.

Suppose the tube to be square, and that the inside
of the square measures exactly one inch each way.
Then an inch of height of the tube will hold exactly
one cubic inch of water. Since one cubic inch of
water weighs 252 grains and a half, as much water
as will fill the tube about two feet three inches
and a half high, will weigh a pound (7,000 grains),
and fifteen pounds of water will fill such a tube
between thirty-three and thirty-four feet high. And
these respective weights measure the pressure of two
columns of water, one twenty-seven and a half inclies
high, and the other nearly thirty-four feet high, on a
square inch of the surface on which they rest.

The specific gravity (§ 24) of lead is 11*45 i ^'"^
other words it is about eleven and a half times denser
than water. Therefore if a bar of lead cut square
and one inch in the side, and rather less than lyth
of the height of a column of water, is slipped into
the tube in place of the water, it will exert the same
pressure on the bottom.

And now comes a difference between the lead
and the water, which depends on the fluidity of the
latter. The lead exerts no pressure on the sides of
the tube, but the water does. If a small hole is cut
in the side of the tube close to the bottom, and
stopped with a cork, the lead will not press upon
the cork. But if the column of water is high enough

OBJECTS.] WTkODUCTORV, 30

the cork will be driven out with as much force as
before, so that the water presses just as much side-
ways as downwards. It is easy to satisfy oneself of
this by inserting a long glass tube, with its lower end
bent at right angles and fitted with a cork, into the
side of the wooden pipe. The water will at once
rise in the tube to the same height as it has in the
pipe. Whence it is obvious that the pressure of the
water on any point of the side is exactly equal to the
vertical pressure at that point ; for the pressure outwards
is exactly balanced by that of the vertical column in
the tube inwards. The water in a watering-pot always
stands at the same level in the can and in the spout.

If a glass tube is bent into the shape of a U, and
water is poured into it, the water w ill always stand at
the same level in the two legs of the tube, whatever
the shape of the bend may be, or the relative capa-
cities of the two legs, or the inclination of the tube.

And this must needs be so, for the force with which
the water tends to flow out of the one half of the
arrangement depends on the vertical height' of the sur-
face of the water above the aperture of exit; so that
any column of equal vertical height must balance it.

That a column of water will stand at exactly the
same level as any other with which it communicates,
may be seen still more simply by placing a glass tube,
open at each end, in a basin of water. However the
tube may be inclined or bejit, whether its lower end is

' Vertical height is the height measured along a line drawn
from the surface of the water perpendicularly to the surface of the
earth. A plumb-line is a string to one end of which a weight
is attached and thus hangs suspended. If tlie other end of the line
is brought opposite the surface of the water the direction of
the string answers to the line of vertical height.

40 SCIENCE PklMEkS. JMAtERlAt.

wide or narrow, the column of water inside it will be
at exactly the same level as the water outside it. Yet, of
course, the rigid glass walls of the tube cut off all
communication between the column of water inside
it and the rest, except at the bottom.

In a well-ordered town, water is supplied to every
house and can be drawn from taps placed in the
highest stories. These are fed by pipes which lead
from a cistern at the top of the house. This water is
brought from a large pipe, or main, in the street, by
a smaller house-pipe, which is often made to twist
about in various directions before it reaches the
cistern at the top of the house into which it delivers
the water. If you followed the main, you would find
that it took a long course up and down, beneath the
pavement of the streets, until at last it reached the
water-works. Here you would find that the main
was connected with a reservoir; and either this reser-
voir is at a greater height than any of the cisterns
into which the water is delivered, or there is some
means of pumping the water from it to that height on
its way to the main. Thus the reservoir, the main,
and the house-pipe form one immense U-tube, and
the water in the house-pipe tends to rise to the same
level as that of the water in the^reservoir, and hence
flows into the cistern when the supply-pipe is open.

28. The Transference of Motion by Moving
Water : the Momentum of Moving Water.

Suppose a wooden vat with a horizontal tap, the
sectional area* of the tube of which is one square inch,

' The sectional area of a tube is the surface occupied by its
cavity when it is cut across. It would be represented by the

OBJ ECTs. i IN TkOb UC TOk V. 4 1

inserted close to the bottom, to be filled with water
up to ICO inches above the tap. Then supposing the
tap to be shut, the pressure upon its sectional area will
be 25,250 grains, or rather more than three pounds
and a half — and there is the same pressure on every
square inch of the bottom of the vat.

If the tap is now turned, the water nearest to it
being unsupported on its outer side, the pressure on
the inner side sets it \x\ motion, and it flows out in a
stream. At first the stream shoots out violently and
the water is carried to a long distance. That is to
say, the weight of the column of water 100 inches
high acts as a force, or cause of motion, upon the
water nearest the tap, and this water is forced out
with a velocity depending on that force in a
horizontal direction. Now suppose that you take a
common toy cup-and-ball and bring the ball into the
way of the stream of water. The stream will at once
strike the ball and drive it in the same direction as
that which it is itself taking. The power which the
moving water has of transferring or communicating
motion to a body which is at rest, but free to move
as the ball is, is due to its momentum. The
greater the mass of the stream and the more rapidly
it moves, the more motion will it communicate to the
ball, or the heavier the ball it will move. Close to
the mouth of the tap the direction of the stream is
horizontal; but it very soon begins to bend down-
wards, and describing a rapid curve, comes to the
ground. It does this for just the same reasons that
a stone thrown horizontally describes a curve, and at

surface of a piece of cardboard, like the wad of a gun, iust
large enough to go into the lube.

42 SCIENCE PRIMERS. Imaierial

length strikes the ground; and, in fact, the stream may
be regarded as so much water thrown horizontally.

These reasons are two: firstly, as soon as the water
has left tlie tap it is an unsupported heavy body; and,
as such, it begins to fall to the ground. Secondly, the
momentum of the water is continually being dimin-
ished by the resistance of the air through which it
passes. For, although the air which surrounds us is
so thin and movable a body that we ordinarily take
no notice of it — the fact that it offers resistance to
bodies which move through it is easily observed;
as, for example, in using a fan. The water has to
overcome this resistance, and its momentum is
proportionally diminished.

If, when the water leaves the tap, the air and gravi-
tation were alike abolished, the water, keeping its
momentum, would travel for ever in the same
direction.

As the water runs out, it will be observed that the
velocity of the stream becomes less and the curve
which it describes sharper, so that it comes to the
ground sooner; and finally, when the vat is nearly
empty, the stream falls nearly vertically downwards.
The reason of this is that the level of the top of
the water is gradually lowered; consequently, the
height of the column which presses on the water close
to the tap is gradually lessened, and therefore its
weight is diminished. But this weight or pressure
is the cause of the motion of the water, and as the
cause diminishes the effect of that cause must diminish.
Therefore the momentum of the water is gradually
lessened and it is carried less and less far horizontally
in the time which it takes to fall to the ground;

oHjECTs.] WTRODVCTORV. 43

until finally, it acquires no appreciable horizontal
motion at all, and so falls vertically downwards from
the mouth of the tap.

29. The Energy of Moving Water.'

If a short pipe bent at right angles like the letter
L is fitted by one arm on to the end of the tap,
while the other is turned vertically upwards, and the
vat is full as before; when the tap is turned, the
water will shoot up into the air, and after rising for a
certain distance will stop, and then fall. In fact we
shall have a fountain.

Observe the difference between the vertical jet of
water and the horizontal jet. If we leave the resist-
ance of the air out of consideration, the water in the
horizontal jet has no obstacle to overcome; and it might
go on for ever, if its weight did not gradually cause
its path to become more and more bent towards the
earth, against which it eventually strikes.

When the jet is vertical the case is altered. The
water thrown up vertically constantly tends to fall
down vertically, as any other heavy body would do,
and its momentum has to overcome the obstacle of
its gravity. Any given portion of the water is, in fact,
acted upon by two opposite tendencies, momentum
urging it up, and gravity pulling it down. Now if two
equal tendencies exactly oppose one another, the body
upon which they act does not move at all; while, if
one is stronger than the other, the body moves in the
direction of the stronger.

Thus a portion of water which has just left the
spout shoots up, because the velocity with which it is
impelled upwards is sufficient to carry it through a

44 SC/£Arc£ PRlxMERS. [matkrial

greater space in a given time, say a second, than tliat
tlirough which its gravity would, in the same time,
impel it downwards.

But the distance wliich the water will travel during
this second will be the difference between the distance
which it would have ascended if there had been no
gravity forcing it down, and the distance which it
would have descended if there had been no momentum
driving it up; and, at the end of the second, the rate of
its motion upwards, or its velocity, will be proportion-
ally slower. Thus, at the end of the first second, the
water has spent a certain portion of its momentum in
overcoming its gravity. And as there is nothing to
make good the loss, it would, if left to itself, travel
more slowly, or over a less distance, in the second
second than it tended to do in the first. But though
the momentum of the water is diminished, its gravity,
weight, or tendency to fall downwards, for a given
distance in a second, remains exactly what it was, and
operates in the course of the second second to exactly
the same extent as in the first. Hence, at the end of
the second second, the distance through which the
water travels upwards is still smaller, and its velocity
is still more diminished. It is obvious that, however
great the disproportion between momentum and
gravity to start with, gravity must gain the day in the
long run under tliese circumstances. The store of
momemtum will beusedup;and, afteramomemtary
rest, the water, reduced to the condition of a body
without support,will begin to becarried downwards
by the unopposed action of gravity.

The ca-3e is similar to that of a boy sculling a boat,
the bows of which ar^, suddenly seized and the boat

OBJECTS.] INTRODUCTORY. 45

thrust violently backwards by a strong man. The
boat will go stern-foremost rapidly, at first, but every
stroke of the boy's oar at the stern will retard its
backward motion ; until, at length, the stock of mo-
mentum conferred upon it by the man's thrust will
be completely exhausted in working against the boy,
and the boat, after a momentary rest, will resume its
onward course. The distance to which the boat will
be propelled backwards will evidently depend upon
the amount of muscular power which the man, as it
were, suddenly capitalizes in the boat, and which the
boat then slowly pays out.

We call people who possess much muscular or other
power energetic ; and we estimate their energy by
the obstacles they overcome, or, in other words, by
the work they do. In the present illustration the
man's energy would be measured by the distance to
which the boat was propelled before it stopped.

It is easy to transfer this conception of energy,
as the power of doing work, to inanimate things ; and
thus when a body in motion overcomes any kind of
obstacles in its way. parting with its momentum and
more or less coming to rest in the process, we say
that it has energy and that it does work.

The energy of moving water is thus measured by
the intensity of the opposing forces which it can over-
come multiplied into the distance which it can travel
before that energy is exhausted ; that is to say, by
the work it does before it is itself reduced to a state
of rest In the case under consideration, the energy
by which gravity is overcome, for a greater or less time;
depends upon the velocity of the stream ; and this again
depends upon the height of the water in the vat

46 SCIENCE PRIMERS. [material

above the tap. Just as the energy of the horizontal
stream diminished as the level of the water became
lower, so does the energy of the vertical stream di-
minish. Hence, as the vat empties, the jet becomes
shorter and shorter, until at last it sinks down to
nothing.

The energy of moving water makes it, under some
circumstances, one of the most destructive of natural
agents ; and, under others, one of the most useful
servants of man. A stream is water falling down hill
with a velocity depending upon the inclination of its
bed. As it falls it acquires momentum and, hence, en-
ergy ; and thus a mountain stream, suddenly swollen by
rain or melting snow, will tear away masses of rock
and sweep everything before it. Nothing can look softer
or more harmless than a calm sea, but if the wind
sweeping over its surface puts the water in motion, it
strikes upon the shore with terrific force ; and its en-
ergy is expended in throwing up great waves, which
lift vast blocks ordrive masses of shingle up the beach.

In all kinds of watermills it is the energy of more
or less rapidly falling water which is turned to account.
The water is made to flow against buckets or floats
attached to the circumference of awheel. Each bucket
or float is therefore an obstacle to which the water
transfers some of its own motion ; it moves away and
thus makes the wheel to which it is fastened turn.
But the turning of the wheel brings a new obstacle in
the way of the stream. This is treated in the same
fashion, and the wheel turns still further, thus intro-
ducing another obstacle in the way of the stream upon
which the same effect is produced. Thus each float,
or bucket, is a means by which some of the momentum

OBJECTS.] INTRODUCTORY. 47

of the stream is, as it were, caught and transferred to
the water-wheel, which consequently turns round with
a certain velocity.

But this water-wheel is now a mass of matter in
motion, and therefore itself contains a store of energy
or power doing work. If a cord with a weight
at the end of it were fastened to the axle of the
wheel the cord would be wound upon the axle, and
the weight could be raised, or, in other words, so
much work would be done by the turning of the
wheel and we should thus have a rough measure of
the amount of energy which had been given up by the
stream to the wheel.

The machinery of the mill is simply a set of con-
trivances for transferring the energy stored up in the
water-wheel to the place in which work has to be
done. In a flour-mill, for example, a series of wheels
carries it from the water-wheel to the grindstones, which
it sets in motion.

30. The Properties of Water are Constant.

If, whenever there is a shower, you catch some rain-
water, you will find that it possesses all the properties
which have been described. It will be found to be
an almost incompressible liquid, an imperial pint of
which weighs about a pound and a quarter. It would
make no difference if the rain-water were collected in
Africa or in New Zealand; or if it had been obtained
centuries ago and kept bottled up ever since. And
there is every reason to believe that rain-water will
have exactly the same properties a hundred or a
thousand years hence. So far as the properties of

48 SCIENCE PRIMERS. [material

rain-water are concerned the order of nature is
constant.

This, however, is by no means the same thing as
saying that the properties of water are always the
same. In fact the properties of the substance, water,
vary immensely according to the conditions to which
it is exposed; but, under the same conditions, tlieyare
the same, so that we may still say that so far as
water is concerned, the order of nature is constant.

31. Increase of Heat at first causes Water
to Increase in Volume.

It has been seen that a certain weight of water
always has the same volume under the same con-
ditions. The most important of these conditions is
the heat or cold to which it is exposed. Water which
has stood for some time in a warm room becomes less
in volume, or contracts, if it is taken into a cool
place; while its volume increases, or it expands, if
it is made hot. The same thing is true of quick-
silver, of spirit, and of liquids in general. A thermo-
meter is simply a small flask — the bulb — with a long
and narrow neck — the tube — filled with as much mer-
cury or spirit as will rise a short distance into the neck.
If the liquid in the bulb is warmed, its volume is in-
creased and it overflows into the tube, increasing the
height of the column of liquid in the tube. If, on
the other hand, the liquid in the bulb is cooled, its
volume is diminished; and, as it shrinks, the column
of liquid in the tube flows back into the bulb, and
the level of the top of the column is lowered.

If a mark is made on the tube, or on a scale fixed
to it. at the point which the liquid reaches when the

ofijficts.] WTkOD OCTOR V. ^t)

bulb is placed in boiling water; and another mark
at the point to which it sinks when the bulb is in
melting ice; and the space between the two marks is
divided into i8o equal parts, each of these parts is
whatis called a " degree" in the thermometers ordinarily
used in this country (called Fahrenheits). And if
the boiling-point is counted as 212° the freezing-point
must be 32° (212 — 32 = 180). With the same amount
of heat the fluid in the tube always stands at the same
degree, and hence the instrument measures tem-
perature.

That hot water is lighter than cold is easily seen
when a bath is filled from two taps, one of hot and
one of cold water, which run at the same time. Un-
less care is taken to stir the water, the top of the bath
will be very much hotter than the bottom. Thus, an
imperial pint of water weighs a pound and a quarter
only at a certain temperature or degree of warmth,
namely at 62° ; if it is made hotter its volume increases,
and therefore its specific gravity diminishes.

It was for this reason that in § 22 the weight of the
same volume of water was said to be constant under
the same conditions; and, of course, the same
qualification must be borne in mind when we speak
of the weight of a cubic inch of water being about
252 and a half grains. Its weight is in fact 252*45
grains only when Fahrenheit's thermometer stands at
62' — but as this is the temperature of ordinary mild
weather, and the expansion or contraction of water
for a degree about this temperature amounts to less
than roffnth of its volume, the weight of a cubic inch
may for all practical purposes be taken as 252 and a
half grains.

60 SCIEJVCE PklMEkS. [>iATtRiAL

32. Increase of Heat at length causes
Water to become Steam.

Thus a change is effected in llie properties of water
by lieating it ever so little. If it is more strongly
heated a still greater change takes place. You
know what happens when a saucepan containing
water is put on the fire. The water gets hotter and
hotter, then it begins to simmer, and finally, when
it reaches 212°, it boils away into steam, which passes
into the air and disappears. If the boiling is carried
on long enough all the water vanishes. It looks at
first as if the water had been destroyed by the heat.
In reality, however, not a particle of water has been
destroyed. It has merely changed its state. The
heat has altered it from the state of liquid water into
that of gaseous water, vapour or Steam.

Try the same experiment with a tea-kettle instead
of a saucepan, but only put a little water in the tea-
kettle, and shut the lid well down. Then, as soon as
the water begins to boil, the steam will shoot out of
the spout in a jet; and this will go on as long as any
water remains in the kettle.

The steam, as it comes out of the spout, is so hot
that it will scald you if you put your finger in it. But
you may satisfy yourself that it is very hot, without
scalding your fingers, by holding a stick of sealing-wax
in it. The wax will soften, just as if you held it before
the fire. Moreover, if you look through the steam, just
where it leaves the spout, you will see that it is quite
transparent ; it is only at some little distance from
the spout that it loses its transparency, changes into
A white opaque cloud, and rapidly vanishes in the ain

OBJECTS.] tNTkObtJCTOkV. 5i

33. The taking away of Heat from Steam
causes the steam to change into Hot Water.

Now take a cold spoon, or a cold plate, and hold it
against the j-it of steam, for a moment or two.
When you take it away, you will find that it is quite wet,
being covered with drops of warm water, and, more-
over, the cold spoon, or plate, has become warm.
And if you fit a long cold metal pipe to the nozzle
of the tea-kettle, you will find that no steam at all
issues from the end of the pipe, but only water, while
the pipe becomes warmed.

Thus the heat passes from the fire into the sauce-
pan, or kettle, and thence to the water which they
contain; the water gets hotter and hotter, and, when
it has taken in a certain quantity of heat, it becomes
steam, or vapour of water. When the steam comes
against the cold plate, or passes through the cold
pipe, it gives up the heat it has taken in to the plate,
or the metal of the pipe. They carry off the heat
which kept the water in a condition of a vapour,
and so it passes back into the condition of liquid.

Thus steam and water are two conditions of the
same thing, water ; they are effects of the quantity
of heat which the water has taken in.

34. When Water is changed into Steam,
its Volume becomes about 1,700 times greater
that it was at first.

If you could measure and weigh the water in your
kettle to begin with, and then measure and weigh all
the steam into which the heat of the fire changes it,
you would find that the bulk of the steam was nearly
1,700 times as great as the bulk of the water, though

55 SC/EJVCE PRtMEHS. [matkkial

the weight of the steam would be exactly the same
as that of the water. If you had a small square cup
like a die. the inside measure of which was exactly
one inch each way, it would hold one cubic inch of
water. If this cup full of water were heated till all
the water was turned into steam, the steam would
nearly occupy a cubic foot; since there are 1,728
cubic inches in a cubic foot. A cubic inch of water
weighs 252I grains, and the steam into which it is
converted has just the same weight. Thus we may
say that steam is water expanded by heat into a
vapour which is of 1,700 times less specific gravity than
water. On the other hand, a pint of steam allowed
to cool, becomes converted into a quantity of water,
which measures only TroTyth of a pint, though it weighs
just as much as the whole pint of steam did. The
steam, therefore, is condensed to a T^Vuth of its
volume of water.

The power with which water expands when it is
converted into steam is very great. If you were to
stop up the nozzle of the tea-kettle, the steam, inside
the kettle, in trying to expand, would burst open
the lid; and if you were to fasten down the lid, it would
pretty soon burst the kettle itself. You sometimes
hear of the strong boilers of steam-engines being
burst in this way.

35. Gases or Elastic Fluids. Air.

Here is a glass flask with a long neck and an open
mouth. If we pour water in at the mouth until it
rises to the lip we say that the flask is full of water.
If we now pour the water out we say that the flask is
empty. But is it empty? Press the flask mouth

OBJECTS.] INTRODUCTORY. 53

downwards into a glass jar full of water. If the flask
were empty there would be no reason why the water
should not enter the neck of the flask and stand at
the same height inside the neck as it does outside.
If you take an " empty" glass tube open at each end
and press it down into the water, the water inside and
the water outside will stand at the same level. But if
you put your finger on the upper end of the tube so
as to convert it into a closed vessel, the water will
enter the lower end only a little way. So with the
flask, the water enters the neck only a little way.
Hence there is something inside the " empty" tube
and in the "empty" flask; something which is mate-
rial, because it occupies space and offers resistance.
In fact the flask is full of that form of matter which
is termed air, a thick coat of which surrounds the
earth as the atmosphere. Air has weight, as you
will learn more fully by and by; and that air in
motion can transfer that motion to other bodies you
are taught by the effects of the winds, which are
merely air in motion.

Air therefore has all the characters of a material
substance. Moreover it is a fluid, for it fits itself
exactly to the shape of any vessel which contains it;
its parts are very easily moved, or we should feel its
resistance every time we move a limb; that it " flows"
is seen in every breeze and every time you use a pair
of bellows, when the air is driven in a stream out of
the nozzle; and it presses on all sides anything
contained in it.

But though air is a fluid it is not a liquid. In the
first place it is very compressible. We saw that the
wat^r entered a little way into the tube or the neck of

54 SCIENCE PRIMERS. [material

the flask in the preceding experiment. The reason
of this is that the water compresses the air into a
smaller volume. A bag full of air, such as a common
air-cushion, can be squeezed till the air in its interior
occupies a much smaller volume; and, if you treat a
syringe full of air in the same way as the syringe full
of water was treated, you will find, if the piston fits
well, that it can be driven down some distance and
then springs back again. Air in fact is not only a
compressible, but it is an elastic fluid or gas. Heat
expandsair just as it expands water, but the expansion
of air for the same degree of heat is much greater.

zd. Steam is an Elastic Fluid or Gas.

In all the properties which have been mentioned
water in the form of steam is an elastic fluid or gas
like air.

If a little water is placed in the flask mentioned
in the preceding section all the "empty" part of the
space will contain air. If the flask is now made hot
the water will at length boil, bubbles of steam forming
in the water and breaking at its surface. By degrees,
the air, whicli at first lay above the water, will be
driven out; and if the whole flask is kept hot, the
'' empty" part of it will be full of the gaseous water,
which is transparent and colourless like air. The
steam flows out of the mouth of the flask still a clear
and colourless gas; but it soon cools and becomes
condensed as a cloud of small particles of fluid water.

Steam is lighter than air, and hence it rises in the
air, just as bodies which are lighter than water rise
in water.

OBJECTS.] TA'TRODUCTOKV, 55

37. Gases and Vapours.

Air is as much a gas in the coldest winter as it is in
the hottest summer. But air can be liquefied by ex-
y)osing it to a very low temperature, while, at the same
time, it is subjected to an extremely great pressure,
rhus, the difference between gases like air, which are
condensed with extreme difficulty, and gases like
steam, which are condensed easily, is only one of
degree. Nevertheless there is a certain convenience
in distinguishing those gases, which, like steam, are
easily condensed as vapours. In what we ordinarily
call steam, all the water of which it is composed re-
mains gaseous only at and above the temperature of
boiling water (212^ Fahrenheit). Cooled ever so
little below this point, most of it becomes condensed
into hot liquid water. However, it must be recol-
lected that though that particular form of gaseous
water which we call steam exists only at and above
the temperature of boiling water, yet water is capable
of existing in the gaseous state down to the freezing-
point.

Suppose that when our boiling flask contained
nothing but water and steam, the mouth were stopped
and the lamp removed. Then, so long as the tem-
perature of the whole remained at that of boiling
water, every cubic inch of steam above the water
in tlie flask would weigh about hh of a grain, since
100 cubic inches weigh about 15 grains. Suppose the
capacity of the flask, exclusively of the fluid water
in it, to be 100 cubic inches. Then, to begin with,
the gaseous water which it contains will weigh 15
i^rains. If the flask is now allowed to cool, more
>ind more of the gaseous water condenses into the

56 SCIENCE PRIMERS. [material

fluid state; but, even down to the freezing-point, some
water will remain in the gaseous state and will fill that
part of the flask which is unoccupied by the fluid water.
At blood-heat (98°) the gaseous water weighs only
about a grain, thought it still occupies 100 cubic inches;
at the ordinary temperature of the air it weighs not
more than ird of a grain; while, at the freezing-point,
its weight is only ith of a grain. But inasmuch as
there is less and less actual weight of water in the
same volume of gaseous water as the temperature
falls, it follows that the density, or specific gravity, of
the gaseous water must be less the lower the tem-
perature. Moreover, while, at the boiling-point,
gaseous water or steam resists compression with
exactly the same force as air does, the lower the
temperature the more easily compressible is the
gaseous water.

Suppose an elastic bag were to be tied on to the
nozzle of a kettle full of boiling water. If the bag
were kept as hot as the boiling water it would become
fully distended, and maintain its shape in spite of
the pressure of the air upon all sides of it. If the bag
were taken away it would retain its shape so long as
it was kept as hot as boiling water; but, if it were
allowed to cool, it would gradually become flattened
by the outside air squeezing up the less and less resist-
ing gaseous water of the lower temperatures. Hence,
when the stopped flask has been allowed to cool, the
air rushes in with great violence if it is opened.

38. The Evaporation of Water at ordinary
Temperatures.
If some water is poured into a saucer and is

OBJECTS.] INTRODUCTORY, 57

allowed to stand even in a cool room or in the open
air, you know that it sooner or later disappears. Wet
clothes hung on a line soon dry — that is to say, the
water clinging to them disappears or evaporates.
The disappearance of the water under these circum-
stances results from the property just mentioned. In
fact, it becomes gaseous water of the density appro-
priate to the temperature, and as such mixes with the
air as any other gas w^ould do. And as the sea,
lakes, and rivers, are constantly giving off gaseous
water into the air in proportion to the temperature,
it is not wonderful that the atmosphere always contains
gaseous water.

Air is said to be moist when the weight of water in
a given quantity, say loo cubic inches, is as much, or
nearly as much, as can exist in the state of gas at the
temperature. Under these circumstances, if the tem-
perature is lowered even a very little, some of the
gaseous water is converted into liquid water. We
see this in hot moist weather, when the outside of a
tumbler of fresh drawn cold spring water immediately
becomes bedewed. The gaseous water in immediate
contact with the tumbler, in fact, is cooled down below
the point at which it can all exist as gas, and the
superfluity is deposited as dew. In such days wet
clothes do not dry well, because there is, already,
nearly as much gaseous water in the atmosphere as
tile amount of heat marked by the thermometer can
maintain in that state.

39. When Hot Water is cooled, it Con-
tracts to begin with, but after a time Expands.
We have now seen whac a wonderful change i§

58 SCIENCE PRIMERS. [material

brought about by heating water. At first, it ex-
pands gradually and slightly; but, when it reaches the
boiling-point, it suddenly expands enormously, and is
no longer a liquid, but a gas.

On the other hand, if warm water is allowed to
cool, it gradually contracts till it reaches the ordinary
temperature of the air in mild weather; but, if the
weather is very cold, or if the water is cooled
artificially, it goes on contracting only down to a
certain temperature (39 ), and then begins to expand
again. In this peculiarity water is unlike all other
bodies which are fluid at ordinary temperatures.
Hence the temperature of 39° is that at which pure
water has its greatest density or specific gravity, and
water at this temperature is heavier, bulk for bulk,
than the same water at any other temperature. There-
fore if water at the top of a vessel is cooled down
to this temperature, it falls to the bottom, and if the
water at the bottom of a vessel is cooled below this
temperature it rises to the top.

40. Water cooled still further becomes the
transparent brittle solid Ice.

Our tumbler of water, if put out of doors on a cold
winter's night, would gradually cool until it assumed a
temperature of 39° throughout. Cooling below this
temperature, the water so cooled would gradually
accumulate at the ssurfaceby reason of its less density,
and its temperature would fall till the thermometer
placed in it marked 32°. As soon as this upper water
cooled ever so little below 2f^°^ a film like glass would
form on its surface by the conversion of the coldest
fluid water into solid water or ice. And if all the

r>BjECTS.] INTRODUCTORY. 5q

water cooled down to the same degree it would all
gradually change into the same kind of substance.

In this condition water is solid. It occupies space,
offers resistance, has weight and transmits motion as
the water did, but if you shake it out of the tumbler in a
cold place it retain its form without the least change.
If you press it, it proves to be exceedingly hard and
unyielding; and, if the pressure is increased, it be-
comes crushed and breaks like glass. It may thus be
crushed to powder, and the ice powder can be formed
into heaps as if it were sand.

Just as any quantity of steam has exactly the same
weight as the water which was converted into it by
heat; so the ice has exactly the same weight as the
water which has been converted into it by taking away
heat.

41. Ice has less Specific Gravity than the
Water from which it was formed.

But though the ice in the tumbler has the same
weight as the water had, it has not the same volume.
The expansion which began at 39° goes on, and when
water passes into the solid state its volume is about
iS-th greater than it was at 39°. Taking water at this
temperature as i.o, ice has a specific gravity of o'9i6.

But although water in freezing expands only to this
small amount, it resembles steam in the tremendous
force with which it expands. If you fill a hollow
iron shell quite full of water, screw down the open-
ing tight, and then put it in a cold place where the
water may freeze, the water as it freezes will burst
the iron walls of the shell. You know that when the
winter is severe, the pipes by which water is brought

6o SCIENCE PRIMERS. [material

to a house often burst. This is because the water in
them freezes, and, being unable to get out of the
pipe, bursts it, just as you may burst a jacket that is
too tight for you by stretching yourself. Among the
bare hill-tops, or on the face of cliffs exposed to the
weather, the strongest and hardest rocks are every
winter split and broken, just as if quarrymen had
been at work at them. In the summer the rain-
water gets into the little cracks and rifts in the
stone and lodges there. Then the winter comes
with its cold and freezes the water. And the water
bursts the rocks asunder just as it bursts our water-
pipes.

42. Hoar Frost is the Gaseous Water
which exists in the Atmosphere, condensed
and converted into Ice Crystals.

In the winter-time you often notice, on a clear
sharp night, that the tops of the houses and the
trees are covered with a white powder called hoar
frost ; and, on the windows of the room when you
wake up, you see most beautiful figures, like delicate
plants. Take a little of tlie hoar-frost, or scrape
off some of the stuff that makes the window look
like ground glass, and you find that it melts in
your hand and turns to water. It is in fact ice.
And if you look at the figures on the window pane
with a magnifying glass you will see that they are
made up bits of ice which have a definite shape,
and are arranged in a regular pattern. Each of these
definitely shaped bits of ice has been formed in the
following way. The air in ihe room is much warmer
than that outside, and there is m ,ed with it nearly as

objECTs.] tMTRObUCTORV. 6t

much water, derived from the breath and the evapora-
tion of moist surfaces, as can maintain itself in the
gaseous state at the temperature. The window-
panes, being thin, are cooled by the outside air,
and of course the gaseous water inside the room,
when it comes in contact with the cold window-
panes, becomes condensed on them into fine drops
of cold water. The panes becoming colder and
colder, these minute drops at last freeze, and the
water not only becomes solid, but it crystallises ;
that is to say, the little solid masses take on more or
less regular geometrical forms with flat faces, inclined
to one another at constant angles, so that they re-
semble bits of glass cut according to particular fixed
patterns. All ice is in fact crystalline, but in ice
which has been formed from thick sheets of water, the
crystals are so packed together that they cannot be
distinguished separately.

43. When ice is warmed it begins to change
back into Water as soon as the Temperature
reaches 32.

A lump of ice brought out of the open air in very
cold weather may have a temperature of 30°, or 20°, or
lower. If such a lump is brought into a warm room
it gradually becomes warmer, but remains unchanged
otherwise, until it has risen to 32\ Then it begins to
melt, and remains at 32* as long as it is melting; and
the water which proceeds from it is at first also at 32°.

If you were to throw a lump of ice into the middle
of a hot fire, so long as a particle of ice remained as
such, it would have a temperature of 32° and no more.
This is a fact exactly parallel to that which is observeci

52 SCIENCE PRIMERS.

when water is raised to the boiling-point. So long a^
any of the water remains unconverted into steam it
becomes no hotter. Moreover the steam itself is at
first at 212°.

44. Ice the solid, Water the liquid, and
Steam the gas, are three states of one na-
tural object ; the Condition of each State
being a certain Amount of Heat.

Ice, liquid water, and steam, are three things as
unlike as any three things can well be. What do we
mean then by saying that they are states of one sub-
stance, water?

What we really mean is that if we take a giveii
quantity of water, say a cubic inch, and change it
first into ice and then into steam, there is something
which remains identically the same through all these
changes. This something is, in the first place, the
weight of the material substance. The water weighs
252^ grains, the ice into which it is converted weighs
252^ grains, and the steam produced from it weighs
252^ grains. In the second place, the same force
would cause the ice, the water, and the steam, to
move with the same rapidity; and, when set in motion,
they would produce the same effect upon anything
movable against which they struck.

In the third place, when you study chemistry,
you will learn that the ice, the steam, and the liquid
water, would yield the same weight of the same twa^
gases, oxygen and hydrogen, and nothing else#
Every one cubic inch of water, 1,700 cubic inches of
steam, and itt cubic inch of ice, yield 2813 grains o{

uRjEcts] INTRObUCTOkV. e3

hydrogen, vvilli 224 A grains of oxygen, and noth-
ing else. (See § 50.)

As there is not the slightest difference in weight
between a given quantity of water and the ice, or the
steam, into which it may be converted, it is clear that
the heat which is added to or taken from the water
to give rise to these several states, can possess no
weight. If then heat is a material body, it must be
devoid of weight — and hence, in former times, heat
was called an imponderable substance. It was
thought to be a kind of fluid, called caloric, which
had no weight, and which drove the particles of
bodies asunder, when it entered them as they were
heated, and let them come together as it left and
they grew cool.

45. The Phenomena of Heat are the
Effects of a rapid Motion of the Particles of
Matter.

This much, however, is certain : that heat can be
caused by motion. Every boy knows that a metal
button may be made quite hot by rubbing it. A skilful
smith will hammer a piece of iron red hot. The axles
of wheels become red hot by rubbing against their
bearings^ if they are not properly lubricated ; and even
two pieces of ice may be melted by the heat evolved
when they are rubbed together. And there are
abundant other reasons, as you will find when you
study physics, for the belief that the sensation we
call heat, and all the phenomena which we ascribe
to heat, are the effects of the rapid motion of matter.

However, a quiescent body may be made hot with-
out exhibiting the least appearance of motion. The

64 sc/£:J\rCE PkiMEks. twAttkiAL

surface of the water in a tumbler at ioo° is just as
unruffled as that of the same water at 32°. What,
then, is meant by saying that heat is a kind of mo-
tion, and that the greater the heat in any body the
greater the amount of motion in that body?

The answer to this question is tliat the motion which
causes the phenomena of heat, is not a visible mo-
tion of the whole mass of the hot body, but a motion
of the individual particles of which it is composed.
And each particle moves, not straight forward, but
backwards and forwards in the same space, so that
its motion may be roughly compared to that of a pen-
dulum, or to that of the balance-wheel of a watch. It
is in fact a sort of vibratory movement ; each vibra-
tion taking place through a very short distance and
with extreme rapidity. The sensation of heat is
caused by the vibratory movements of the particles
of matter, just as sound is so caused. The prongs
of a tuning-fork which has been struck, certainly
vibrate, for you can see them do so if the note is low.
If you now put your ear at one end of a long piece
of timber and the handle of the vibrating tuning-
fork is placed upon the other end, the vibratory mo-
tion of the tuning-fork will be communicated to the
particles of the wood and will be loudly heard. All
the time the sound is heard the particles of the wood
are vibrating. Nevertheless, the wood as a whole
does not move, but its particles swing backwards and
forwards through such a minute space that their mo-
tion is imperceptible.

But what are these particles of matter which by
their vibration give rise to the phenomena of heat ?

objects] INTRODUCTORW 65

46. The Structure of Water.

We have seen that pure water is perfectly clear and
transparent. The naked eye can discern no differ-
ence between one part and another. In other words,
it has no visible texture or Structure. It does not
follow that it really possesses none, however, for there
are many things which seem to be the same through-
out, or homogeneous, which yet show structure
if they are examined with a magnifying glass. Thus
the surface of a sheet of fine white paper looks per-
fectly even and smooth to the eye; but a magnifying
glass of no great power will show the minute woody
fibres of which it is made up; while, under a power-
ful microscope, the paper looks like a coarse matting.

But if we put a small drop of water on a slide, such
as is used for microscopic objects, and cover it over
with a thin glass so as to spread it out into a film,
perhaps not more than yiir^TTiyth of an inch thick, it
may be examined with the very highest magnifying
powers we can command, and yet it looks as com-
pletely homogeneous and shows as little evidence of
being made up of separate parts as before. However,
this is still no proof that the water is not made up of
little parts, or particles, distinctly separated from one
another. It may merely mean that the particles are
so extremely small that they cannot be distinguished
even by microscopes which magnify four or five
thousand diameters.

It is certain that solid bodies may be divided
into particles so minute that the best microscopes
show no trace of them. Common gum-mastic cannot
be dissolved by water, but it readily dissolves in
strong spirit or alcohol, and mastic varnish is an

66 SCIENCE PRIMERS. [material

alcoholic solution of gum-mastic. If you add water
to mastic varnish, the alcohol takes away the water
and the mastic falls out, or precipitates, as a curdy
solid composed of very visible whitish particles. But
if a drop of the varnish is added to a good deal, say
half a pint, of water and well stirred at the same time,
the mastic, though it is still precipitated as a solid, is
in a state of extremely minute division. No separate
solid particles of mastic are visible to the naked eye,
but the water assumes a faint milky tinge.

This milkiness arises from the presence of solid
particles of mastic diffused through the water; and
yet, if the experiment has been properly managed, a
drop of the fluid may be spread out as before and
examined with the highest magnifying powers, and
nothing can be seen of such particles. So far as
vision goes it might be a drop of pure water. Now
our best microscopes are able to show us anything
solid which has a diameter of TTRFTOth of an inch,
quite distinctly; and probably solid opaque particles
of much smaller size would make themselves ap
parent as a turbidity or cloudiness. The particles of
mastic must be therefore so much smaller than this
that they remain invisible. Hence it follows that
if water were made up of separate particles, or
droplets, nnrWirth of an inch in diameter, and thus
had the structure of a mass of very fine shot, no
microscope that has yet been constructed would enable
us to see even a trace of that structure. We could
not obtain any direct evidence of it.

OBJECTS.] INTRODUCTORY. 67

47. Suppositions or Hypotheses; their
Uses and their Value.

When our means of observation of any natural fact
fail to carry us beyond a certain point, it is perfectly
legitimate, and often extremely useful, to make a sup-
position as to what we should see, if we could carry
direct observation a step further. A supposition of
this kind is what is called a hypothesis, and the
value of any hypothesis depends upon the extent to
which reasoning upon the assumption that it is true,
enables us to explain or account for the phenomena
with which it is concerned.

Thus, if a person is standing close behind you, and
you suddenly feel a blow on your back, you have
no direct evidence of tlie cause of the blow ; and
if you two were alone, you could not possibly obtain
any ; but you immediately suppose that this person
has struck you. Now that is a hypothesis, and it is
a legitimate hypothesis, first, because it explains the
fact ; and, secondly, because no other explanation is
probable ; probable meaning in accordance with the
ordinary course of nature. If your companion
declared that you fancied you felt a blow, or that
some invisible spirit struck you, you would probably
decline to accept his explanation of the fact. Vou
would say that both the hypotheses by which he
professed to explain the phenomenon were extremely
improbable ; or in other words, that in the ordinary
course of nature fancies of this kind do not occur,
nor spirits strike blows. In fact, his hypotheses would
be illegitimate, and yours would be legitimate ; and,
in all probability, you would act upon your own.
In daily life, nine-tenths of our actions are based

68 SCIENCE PRIMERS. [material

upon suppositions or hypotheses, and our success or
failure in practical affairs depends upon the legitimacy
of these hypotheses. You believe a man on the
hypothesis that he is always truthful ; you give him
pecuniary credit on the hypothesis that he is solvent.
Thus, everybody invents, and, indeed, is compelled
to invent, hypotheses in order to account for phe-
nomena of the cause of which he has no direct
evidence ; and they are just as legitimate and neces-
sary in science as in common life. Only the scientific
reasoner must be careful to remember that which is
sometimes forgotten in daily life, that a hypothesis
must be regarded as a means and not as an end ; that
we may cherish it so long as it helps us to explain the
order of nature; but that we are bound to throw it
away without hesitation as soon as it is shown to be
inconsistent with any part of that order.

48. The Hypothesis that Water is com-
posed of Separate Particles (Molecules).

It has been pointed out that we cannot see, and
indeed that there is not much hope of our ever being
able to see, the separate particles of water, even if water
is composed of such particles. But it is perfectly
legitimate to suppose that water is made up of such
particles, if that hypothesis will enable us to explain
the properties of water.

Let us suppose then that any portion of fluid water is
really composed of a prodigious number of particles less
(and probably much less) than a millionth of an inch
in diameter. We may call these particles molecules.'

^ Diminutive of moles, a mass.

OBJECTS.] INTRODUCTORY. 69

We are justified, in accordance with the general
properties of matter (§ 18), in supposing that these
molecules tend to approach one another. But the
fact that water is slightly compressible justifies the
supposition that its molecules are not in actual con-
tact, but that they are separated by interspaces, just as
the motes in the air of a dusty room are so separated.

What is it that keeps the molecules apart? We have
seen that great meclianical pressure brings them but
slightly nearer to one another; hence there is an
equivalent resistance of some kind which keeps them
apart. This resistance must have the same origin as
the sensation which we know as heat, for it has been
seen that diminution of heat diminishes the bulk
of water; that is, allows the molecules to come closer
together; that is, diminishes their tendency to keep
asunder. Increase of heat, on the other hand, in-
creases the volume of water; that is to say, drives the
molecules further apart, or increases their tendency
to keep asunder.

Suppose we call the cause of the tendency of the
molecules of water to come together an attractive
force; and the cause of their keeping apart, which
manifests itself to us as the sensation of heat and is,
as we have seen, in all probability, a rapid vibratory or
whirling motion of the molecules, a repulsive force;
then, in the liquid state, these forces are so adjusted
that the molecules are quite free to move, and yet
hold together.

By adding heat the repulsive force is increased,
until the molecules are about twelve times as far apart
as they were in each direction; while the attractive

76 SCIENCE PRiMEkS. [material

force is overcome, and the molecules fly off in all
directions as soon as they are unconfined. On the
other hand, by taking heat away, the repulsive force
is diminished, until the molecules become inseparable
and the water assumes the solid form.

It is probable that the expansion of fluid water, at a
temperature below 39°, depends upon the molecules
taking up a peculiar arrangement as they approach
one another. If sixteen men are formed into a
column, four deep, and each man a foot from the
other, the same men may stand closer together and
yet form a hoi low square, which occujiies a larger space.
That the molecules of water do take up a particular
order in assuming the solid condition, is shown by
the crystalline form of ice. Each crystal of hoar-
frost owes its shape to the arrangement of its mole-
cules, according to a definite geometrical pattern.

Thus the hypothesis that water is composed of
separate molecules, is useful, for it helps us to some
extent to explain the properties of water. And, when
you study physics and learn the laws of motion, you
will find that there is no end to tlie number of the
truths established by observation and experiment,
which can be explained by this hypothesis. Hence
it may fairly be adopted and employed as a means
of picturing to ourselves the order of nature, so long
as no facts are discovered which are inconsistent
with it.

49. All Matter is probably made up either
of Molecules or of Atoms.

The same reasons which lead to the adoption of
the hypothesis that water is composed of separate

OBJECTS. ] tNTROD UCTOk V. 7 i

particles justify its extension to all forms of matter
whatever.

The metal mercury or quicksilver, for instance,
may be supposed to be made up of distinct particles
of mercury of extreme minuteness, and according to
the temperature, these associate themselves in the
solid (frozen mercury), liquid (ordinary quicksilver), or
gaseous form (vapour of mercury). To whatever treat-
ment pure mercury may be subjected, we cannot get
anything but mercury out of it. The particles of
mercury have never been broken up. Hence they are
generally termed atoms, or particles that cannot be
divided; and mercury is said to be an element, or
a substance which is not compounded of any other
substances.

Here is a case in which it is very useful to dis-
tinguish between fact and hypothesis. The matter of
fact is that, up to the present time, no one has been
able to get out of pure mercury anything but pure
mercury. The statement that mercury is a simple
substance, and therefore never can be broken up into
any other substances, is a hypothesis which future
observation and experiment may or may not confirm.

A hundred and fifty years ago it was universally
believed that water was as much an element as
mercury. But water is now well known to be a
compound. In fact, as has already been said,- the
particles of water may be very readily broken up or
decomposed (in what way, you will learn when
you study chemistry) into two totally distinct sub-
stances, oxygen and hydrogen, which are gaseous
at all known temperatures, though by combining vast
pressure with extreme cold they have recently been

*?2 SCIE^rCE PlilMEkS. twATfeRlAt,

liquefied. Each of these gases, according to our
hypothesis, consists of particles, and since these can
by no known means be further broken up, they are
considered to be atoms like those of mercury.

Nine parts by weight of pure water always yield
eight of oxygen and one of hydrogen. The hypo-
thetical particle, or molecule of water, therefore,
must be composed of atoms of oxygen and hydrogen
havingthis relative weight; and chemists havegrounds
for believing that one atom of oxygen and two
atoms of hydrogen exist in each molecule of water.
If this be so, the structure of water must be more
complicated than we thought at first; and each
particle of water (the molecule) must be a system
composed of three separate atoms.

50. Elementary Bodies are neither de-
stroyed nor is their Quantity increased in
Nature.

It has been seen that when a cubic inch of water
is dissipated by heat, it is not destroyed, but that it
merely changes its form from the fluid to the gaseous
state, while its weight remains unaltered. If the same
cubic inch of water is decomposed into oxygen and
hydrogen gases, the water is indeed destroyed, but
the matter of which it consisted remains unchanged
in weight. If the water weighed 252*5 grains, the
oxygen gas will weigh 224*45 grains and the hydrogen
gas will weigh 28*05 grains. And nothing that man
has been able to do has affected the weight of a
given quantity of either of these gases. So far as we
know, elementary bodies retain their weight under all

06JECTS.] IMTRODUCTORV. 73

circumstances, and can be traced by it whatever shape
they may take. If this is true it follows that, in the
order of nature, matter is indestructible : the
quantity of it neither increases nor diminishes.

Hence it follows that natural things and artificial
things resemble one another in one respect. It is
true of both that the matter of which they are com-
posed is never destroyed and never increased; and
therefore the order of events in nature as much
consists in the joining together and putting apart of
natural bodies by natural agencies, as the order of
events in the artificial world consists in the joining
together and the putting apart of natural bodies by
human agencies.

51. Simple Mixture.

In order to learn the manner in which water may

be broken up into its elements or decomposed,

you must turn to the Primer on Chemistry, But as a

preliminary to the study of that science, it may be

seful to consider some simple cases of composition

d decomposition which are exemplified by water.

If half a pint of water, coloured by putting a little
ink into it, is added to the same quantity of clean
water, the two willreadily mingle; the total quantity of
water will be a pint; and its colour will be just half as
dark as tiiat of the coloured half-pint. This is a case
<A simple mixture. The volume of the mixture
quals the sum of the volumes of the things mixed,
i nd there is no change in the properties of these things.
So when water evaporates, the gaseous water or
vapour mixes with the air in the same way, the mole-
cules of the one body dispersing themselves between

74 SCIENCE PRIMERS. [material

the molecules of the other until there is the same
proportion of each everywhere. In like manner,
sand and sugar may be (and unfortunately often are)
mixed, without any change in the properties of either,
or in the space which they primitively occupied.

On the other hand, oil and water will not mix, how-
ever much you may stir the two together; and the oil,
being the lighter, rises to the top as soon as the fluid
is quiet. Nor will quicksilver and water mix, but the
quicksilver, being very much heavier than the water,
rushes to the bottom of the vessel into which the two
are put. Neither will sand nor iron filings mix with
water; as heavier bodies, they also sink to the bottom.
Nor does powdered ice, though it is water in another
shape, mix with ice cold water; as a lighter body it
floats at the top.

52. Mixture followed by Increase of Den-
sity ; Alcohol and Water.

Strong spirit, or alcohol, is aclear transparent fluid
which looks like water, but is a very different substance.
For example, it boils at a much lower temperature, it
burns with a blue flame, it has intoxicating properties,
and, likeoiljit is very much lighter than water. Hence,
if coloured spirit is poured gently upon the surface of
water the spirit rests upon the water. Suppose, now,
that we take a tall measure graduated into ten equal
parts. Fill the lower five with water, and then, very
gently, pour in the strongest alchool, coloured in
some way, until the tenth mark is reached. We shall
have five volumes of water below, and an equal quan-
tity, or five volumes, of coloured alcohol above.
Where the two are in contact, the colour will be

OBjECTs.l INTRODUCTORY. 75

diffused into the water for a short distance, but not far,
showing that only a slight mixture is taking place.
This, however, is not because the two fluids mingle
with difficulty; for, with slight stirring, they mix com-
pletely, and you have a fluid the colour of which is
about half as intense as that of the alcohol, and many
of the other properties of which are intermediate
between those of pure alcohol and those of pure
water.

Thus far, nothing further than simple mixture, as
when coloured water was added to pure water, seems
to have occurred; but, in reality, something more has
happened. In the first place, the mixture is a good
deal warmer than either of its components; that is to
say, heat has been generated. In the second
place, if you measure the volume of the whole fluid
after it has cooled, it no longer stands at the mark
ten, but distinctly lower, or about nine and three-
quarters. As the volume of the mixture is less
than the sum of the volumes of its two components,
it follows that the density of the mixture must
be greater than a density midway between that
of the water and that of the alcohol. In other
words, the molecules in the mixture do not occupy
the same space as they did when they were sepa-
rate. The result is the same as if the ten volumes
liad been compressed until they occupied only nine
md three-quarters; so that the effect is a contraction
imilar to that which would be brought about by
taking away heat from the mixture. In fact, as we
have seen, the mixture gives out a quantity of heat.

There is another respect in which the mixture is
unlike both its constituents. It both boils and

^6 SCIENCE PRIMERS. [^^'^terIai

freezes at a much lower temperature than water
does, and at a higher temperature than alcohol does.
In fact pure alcoliol has not yet been frozen. If the
molecules of the alcohol were merely diffused among
those of the water as water is diffused through wet
sand, they ought to pass into the gaseous state at the
same temperature as that at which alcohol boils; and
it would then be very easy to separate alcohol from
water by distillation. But the fact is not so; alco-
hol cannot be obtained free from water by distillation
unless something which holds water very strongly,
such as quicklime, is added, so as to keep all the
water back when the fluid is heated.

Thus alcohol and water, mingled together, give rise
to a fluid which is not a mere mixture, the properties
of which are known if we know the properties of its
components; it is, in strictness, a new body, in which
the molecules of the water and those of the alcohol
aifect one another to a certain extent and modify the
pre-existing properties of each.

This effect of different bodies upon one another
becomes much more manifest when water is brought
into contact with certain solids.

53. Solution : Water Dissolves Salt.

If aspoonful of salt is put into a tumbler of cold water
and the water is stirred, the salt swiftly vanishes from
view ; and, after a time, so far as our sense of vision
goes, the water appears to be just what it was before.
But if the water in the tumbler at first weighed five
ounces and the salt weighed two ounces, the water
in the tumbler will now weigh seven ounces; the
water will now taste salt, the salt is said to be

objects] mTRODUCTORW 77

dissolved, and the solution is called brine.
Moreover, the solution is said to be saturated, for
if you put more salt in it will remain unchanged.
Water, in fact, will dissolve two-fifths of its weight
of salt and no more. If the brine thus formed is put
into a wide dish, so that the water may evaporate; or
if it is heated and the water boiled away ; as fast as the
water diminishes, a quantity of salt, equal to two-fifths
of the water which is converted into steam, returns to
the solid state and falls to the bottom of the vessel.
And when all the water is driven off, the salt which
remains will have exactly the weight, and all the other
l)roperties which it had before it was dissolved by the
Nvater.

Thus, contact with water has had a very singular
effect upon the salt. It appears to have changed one
of the properties of the salt, namely, its solidity,
but to have left all the rest unaltered. We saw just

nv that powdered ice does not mix with ice-cold
water, but that the fragments of ice remain solid. The
moment, however, that the temperature rises, the
cohesion, or sticking together of the molecules,
which is the characteristic of the solid state, comes to

1 end ; they become loose and free to move, and they
mingle with the surrounding water. Or we may say
that the ties which held the molecules of the solid
togetlier are dissolved, so that the solid water becomes
fluid.

The resemblance of this process to the dissolving
of salt in water is so obvious that, in common lan-
guage, it is often said that a lump of salt or of sugar
melts away in water ; but if you try to make salt
fluid by heat, you will have to expose it to a very high

78 SCIENCE PRIMERS. [material

temperature, so that the conversion of salt from the
solid state into the liquid state by solution in cold
water is obviously a very different process from lique-
faction by heat. Nevertheless the result is the same
so far as the condition of the salt is concerned. The
cohesion between its molecules is destroyed, and they
distribute themselves evenly among the molecules of
the water, just as the molecules of steam distribute
themselves among the molecules of air. And, when
you study chemistry, you will learn how it may be
proved that the smallest drop of the solution of salt
contains exactly the same proportion of salt as the
whole does.

If brine is allowed to evaporate slowly, the mole-
cules of the salt arrange themselves, as the water
leaves them, in beautifully regular cubical crystals.
You may see them form easily enough if you watch a
drop of brine gradually dry up under a microscope.
The salt crystals contain nothing but salt. If they
are heated till they become red-hot they pass into the
fluid state ; and when still further heated, the fluid
salt becomes a vapour or gas and, as such, flies off
into the air, or volatilizes.

Thus we see that when salt and water are brought
into contact, the salt undergoes a certain amount of
chan^, while the water does not remain wholly un-
changed. For brine no longer boils at 212°, but re-
quires a considerably higher temperature. The salt, as it
were, holds the water back, and prevents it from assum-
ing the gaseous state under the same conditions as if it
were pure, just as, in the previous case, the water held
the alcohol back ; or we may say that the force of heat
which drives the molecules of liquid water apart, when

OBJECTS.] INTRODUCTORY. 79

steam is formed, has a greater resistance to overcome
when salt is dissolved in the water. And just as
the presence of alcohol lowers tli^ freezing point of
the water with whicli it is mixed, so does the presence
of salt lower the freezing point of water. Sea water,
which is a weak brine, begins to freeze at about 27°;
and the ice which is formed is quite pure, while the
remainder of the sea water becomes richer in salt.

If we mean by attraction that which opposes any
force which tends to separate bodies, then we may say
that the molecules of salt and those of water attract
one another. And such attraction between molecules
of matter of different kinds is called chemical at-
traction.

54. Quicklime and Water : Plaster of Paris
and Water: Combination.

Quicklime is asubstanceobtainedbyheatingchalk or
jmestone to redness. When pure, it is a white hard solid
rhich can be made to pass into the liquid and gaseous
states only at enormously high temperatures. If a
lump of fresh quicklime be placed in a saucer and about
one-third of its weight of water poured upon it, there will
be a great turmoil, heat will be evolved, the water will
disappear, and the lime will crumble down into a soft
white powder. This operation is what bricklayers call
slaking lime. And if no more water has been added
than the proportion mentioned, the pure white powder
which results will be solid and dry, the water having,
to all appearance, vanished.

In the solution of salt we saw a solid become
fluid under the influence of water; in the slaking of
lime the fluid water enters into the structure of a solid.

8o SCIENCE PRIMERS. [material

If more water is added, this solid dissolvesor becomes
liquid, as the salt did, and the solution is called lime-
water. By carefully managed evaporation of the
water the lime may be recovered in the form of crys-
tals, just as the salt was recovered. But there is
this difference, that the salt crystals contain no wa-
ter, while the lime crystals not only contain water,
but contain exactly the same proportion as exists
in slaked lime, that is to say, i8 parts water to 56
parts lime.

The water thus bound up with the lime into a new
solid holds on so firmly to the lime that it requires a
red heat to separate the two. The lime and the water
are said to be chemically combined ; and as the
proportion of lime and water in slaked lime, or lime
crystals, is always the same, they are said to be com-
bined in definite proportions ; and the slaked lime
receives the special name of hydrate of lime.

Gypsum or Plaster of Paris is a dry white
powder. If mixed with a little water it does not slake
after the fashion of quick lime, but the mixture soon
sets or becomes hard; and, at the same time, the
greater part of the water disappears. In fact, it has
combined with the plaster of Paris and forms part of
another hydrate, in which, when the superfluous mois-
ture dries, not a trace of water is to be seen. It is this
property wliich is taken advantage of when plaster of
Paris is used in making casts and moulds. The fluid
plaster is poured over and round the body to be cast;
as a fluid, it applies itself conveniently to all the in-
equalities of its surface; and, when it sets, it retains the
shape which it has thus acquired. Set plaster of Paris
may be perfectly dry; but it nevertheless contains

I

ORjEcrs.J INTRODUCTORY. 81

between t and \ of its weight of water, fixed and
forming an integral part of the solid hydrate. And
if the set plaster is strongly heated, the combined
water is driven off and it returns to its original state.

Gypsum is found abundantly in nature, in the shape
of beautiful transparent crystals which are called
selenite. These crystals have the same composition
as set plaster, that is to say, they are hydrates. A
thin flake of such a crystal viewed with the highest
powers of the microscope appears perfectly homo-
geneous. Nevertheless, there is good reason for the
conclusion that it consists of molecules of water and
molecules of gypsum which hold together so strongly
that they form a hard brittle glassy solid. Moreover,
the molecules of the hydrate itself hold togetlier more
strongly in some directions than in others. It is very
easy to split the crystals lengthwise ; while much more
force is needed to cut them crosswise and then they
do not split, but break.

Glauber's salts and Epsom salts are other exam-
ples of solids which dissolve in water and separate
in the crystalline form as the water evaporates ; and
which, like lime and gypsum, combine with a definite
proportion of water to form crystalline compounds.
In fact, each of these glassy brittle solids contains
more than half its weight of water.

Thus we see that two bodies, of which water is
one, may combine together to give rise to something
different from either. And we are thus led to the
science of chemistry, which tells us exactly how
bodies combine, what comes of their combination,
and how compounds may be separated into their coa*
5tituents»

82 SCIEIVCE PRIMERS. [MATfiRlAL

55. Mineral bodies may take on definite
shapes and grow, or increase in size, by the
addition of like parts.

Water and all the other natural bodies which have
hitherto been mentioned, are what are called mineral
bodies, although, in common use, the term mineral
is usually restricted to ores and metals. Now we have
repeatedly had occasion to remark that, under certain
circumstances, not only water, but many other mineral
bodies, assume regular shapes. The most familiar
example is that of the beautiful imitation of leaves
and foliage which is presented by the ice which forms
on a window in winter. But we have also seen that
common salt, lime, gypsum, Glauber's salts and Ep-
som salts, also assume the crystalline form as they or
their compounds with water are deposited from
their solutions. And if a drop of solution of Glau-
ber's salts or of Saltpetre, is allowed to evaporate
under the microscope, a wonderful spectacle will be
presented. As the salt assumes the solid state, the
crystals suddenly appear in the field of view as needles
and plates disposed in beautiful patterns, which rival
those of hoar frost, though they are quite different
from them. In fact, as you will learn if you study
crystallography, every crystallizable substance has
its proper crystalline forms and never departs from
certain strictly related geometrical figures.

A crystal of any of these substances will grow if
placed under proper conditions. Thus, if a crystal of
common salt is hung by a thread in a saturated solu-
tion of salt, which is exposed to the air, so as to allow
the water to evaporate slowly, the molecules of the
salt which is left behind and can no longer be held

j ECTS. ] TN TkOD VC TOR Y. %%

in solution, deposit themselves on the crystal in regular
order and increase its size without changing its form.
And, in this way, the small crystal may grow
to a great size. The large crystals of sugar candy,
which consist of sugar and water deposited from a
strong syrup or saturated solution of sugar, grow in
the same fashion, upon threads suspended in the
evaporating syrup. In this mode of growth you will
observe that the enlargement is effected by addition
to the outside of the growing body; and moreover the
matter which is added, namely, the salt or the sugar,
already exists as salt in the brine or as sugar in the
syrup.

B. LIVING BODIES.

56. The Wheat Plant and the substances
of which it is composed.

Every one has seen a cornfield. If you pluck up
one of the innumerable wheat plants which are
fixed in the soil of the field, about harvest time, you
will find that it consists of a stem which ends in a
root at one end and an ear at the other, and that
blades or leaves are attached to the sides of the
stem. The ear contains a multitude of oval grains
which are the seeds of the wheat plant. You know
that when these seeds are cleared from the husk or
bran in which they are enveloped, they are ground
into fine powder in mills, and that this powder is the
flour of which bread is made. If a handful of flour
mixed with a little cold water is tied up in a coarse
cloth bag, and the bag is then put in a large vessel

^4 SCIENCE PRtMERS. twATERUL

of water and well kneaded with the hands, it will
become pasty, while the water will become white. If
this water is poured away into another vessel, and the
kneading process continued with some fresh water, the
same thing will happen. But if the operation is re-
peated the paste will become more and more sticky,
while the water will be rendered less and less white,
and at last will remain colourless. The sticky
substance which is thus obtained by itself is called
gluten ; in commerce it is the substance known as
maccaroni.

If the water in which the flour has thus been
washed is allowed to stand for a few hours, a white
sediment will be found at the bottom of the vessel,
while the fluid above will be clear and may be poured*
off. This white sediment consists of minute grains of
starch, each of which, examined with the microscope,
will be found to have a concentrically laminated
structure. If the fluid from which the starch was
deposited is now boiled it will become turbid, just as
white of egg diluted with water does when it is boiled,
and eventually a whitish lumpy substance will collect
at the bottom of the vessel. This substance is called
vegetable albumin.

Besides the albumin, the gluten, and the starch,
other substances, about which this rough method of
analysis gives us no information, are contained in the
wheat grain. For example, there is woody matter or
cellulose, and a certain quantity of sugar and fat.
It would be possible to obtain a substance similar to
albumin, starch, saccharine and fatty matters, and
cellulose, by treating the stem, leaves, and root in a
similar fashion, but the cellulose would be in faf

OBJECTS. ] IN TROD UCTOR V. 85

larger proporlion. Straw, in fact, which consists of
the dry stem and leaves of the wheat plant, is almost
wholly made up of cellulose. Besides this, however,
it contains a certain proportion of mineral bodies,
among them, pure flint or silica ; and, if you should
ever see a wheat rick burnt, you will find more or less
of this silica, in a glassy condition, in the embers. In
the living plant, all these bodies are combined with a
large proportion of water, or are dissolved, or sus-
pended in that fluid. The relative quantity of water is
much greater in the stem and leaves than in the seed.

57. The Common Fowl and the Sub-
stances of which it is Composed.

Everybody has seen a common fowl. It is an
active creature which runs about and sometimes flies.
It has a body covered with feathers, provided with
two wings and two legs, and ending at one end in a
neck terminated by a head with a beak, between the
two parts of which the mouth is placed. The hen
lays eggs, each of which is enclosed in a hard shell.

I you break an egg the contents flow out and are seen
consist of the colourless glairy "white" and the
llow ** yolk." If the white is collected by itself in
Iter and then heated it becomes turbid, forming a
lite solid, very similar to the vegetable albumin,
lich is called animal albumin.
If the yolk is beaten up with water, no starch nor
ellulose is obtained from it, but there will be plenty
'f fatty and some saccharine matter, besides substances
iiore or less similar to albumin and gluten.
The feathers of the fowl are chiefly composed
f horn; if they are stripped off and the body is

96 SCIENCE PRIMERS. [material

boiled for a long time, the water will be found to
contain a quantity of gelatin, which sets into a jelly
as it cools; and the body will fall to pieces, the bones
and the flesh separating from one another. The bones
consist almost entirely of a substance which yields
gelatin when it is boiled in water, impregnated with a
large quantity of salts of lime, just as the wood of the
wheat stem is impregnated with silica. The flesh, on
the other hand, will contain albumin, and some other
substances which are very similar to albumin, termed
fibrin and syntonin.

In the living bird, all these bodies are united with
a great qnantity of water, or dissolved, or suspended
in water; and it must be remembered that there are
sundry other constituents of the fowl's body and of the
egg, which are left unmentioned, as of no present
importance.

58. Certain Constituents of the Body are
very similar in the Wheat Plant and in the
Fowl.

The wheat plant contains neither horn, nor gelatin,
and the fowl contains neither starch, nor cellulose; but
the albumin of the plant is very similar to that of the
animal, and the fibrin and syntonin of the animal are
bodies closely allied to both albumin and gluten.

That there is a close likeness between all these
bodies is obvious from the fact that when any of them
is strongly heated, or allowed to putrefy, it gives off
the same sort of disagreeable smell; and careful
chemical analysis has shown that they are, in fact,
all composed of the elements Carbon, Hydrogen,
Oxygen, and Nitrogen, combined in very nearly

'HjECTS.] INTRODUCTORY, 87

uie same proportions. Indeed, charcoal, which is
impure carbon, might be obtained by strongly heating
either a handful of corn, or a piece of fowl's flesh, in
a vessel from which the air is excluded so as to keep
the corn or the flesh from burning. And if the vessel
were a still, so that the products of this destructive
distillation, as it is called, could be condensed and
collected, we should find water and ammonia, in some-
shape or other, in the receiver. Now ammonia is a
compound of the elementary bodies, nitrogen and
hydrogen; therefore (§ 50) both nitrogen and hydro-
gen must have been contained in th.e bodies from
which it is derived.

It is certain, then, that very similar nitrogenous com-
pounds form a large part of the bodies of both the
wheat plant and the fowl, and these bodies are called
proteids.

59. Proteid Substances are met with in
Nature only in Animals and Plants; and
Animals and Plants always contain Pro-
teids.

It is a very remarkable fact that not only are such
substances as albumin, gluten, fibrin and syntonin,
known exclusively as products of animal and vegetable
bodies; but that every animal and every plant, at all
periods of its existence, contains one or other of them,
though, in other respects, the composition of living
bodies may vary indefinitely. Thus, some plants con-
tain neither starcli nor cellulose, while these substances
are found in some animals; while many animals contain
'^o horny matter and no gelatin-yielding substance.

• that tlie matter which appears to be the essential

SS SCIENCE PRIMERS. [material

I

foundation of both the animal and the plant is the
proteid united with water ; though it is probable
that, in all animals and plants, these are associated
with more or less fatty and amyloid (or starchy
and saccharine) substances, and with very small
quantities of certain mineral bodies, of which the
most important appear to be phosphorus, iron,
lime, and potash.

Thus there is a substance composed of water
-I- proteids + fat + amyloids + mineral matters
which is found in all animals and plants; and, when
these are alive, this substanceistermed protoplasm.

60. What is meant by the word Living ?

The wheat plant in the field is said to be a living
thing: the fowl running about the farm-yard is also
said to be a living thing. If the plant is plucked up,
and if the fowl is knocked on the head, they soon die
and become dead things. Both the fowl and the
wheat plant, as we have seen, are composed of the
same elements as those which enter into the com-
position of mineral matter, though united into com-
pounds which do not exist in the mineral world. Why
then do we distinguish this matter when it takes tlie
shape of a wheat plant, or a fowl, as living matter ?

61. The Living Plant increases in size, by
adding to the Substances which compose its
Body, like Substances ; these, however, are
not derived from without, but are manu-
factured within the Body of the Plant from
simpler Materials.

In the spring, a wheat-field is covered with small

OBJECTS.] lA^TRODUCTORr. 89

green plants. These grow taller and taller until they
attain many times the size which they had when they
first appeared ; and they produce the heads of flowers
which eventually change into ears of corn.

In so far as this is a process of growth, accompanied
by the assumption of a definite form, it might be
compared with the growth of a crystal of salt in
brine : but, on closer examination, it turns out to be
something very different. For the crystal of salt grows
by taking to itself the salt contained in the brine,
which is added to its exterior ; whereas the plant
grows by addition to its interior : and there is not a
trace of the characteristic compounds of the plant's
body, albumin, gluten, starch, or cellulose, or fat, in
the soil, or in the water, or in the air.

Yet the plant creates nothing (§ 50) and, therefore,
the matter of the proteids and amyloids and fats which
it contains must be supplied to it, and simply manu-
factured, or combined in new fashions, in the body of
the plant.

It is easy to see, in a general way, what the raw
materials are which the plant works up, for the
plant gets nothing but the materials supplied to it by
the atmosphere and by the soil. The atmosphere
contains oxygen and nitrogen, a little carbonic acid
gas, a minute quantity of ammoniacal salts, and a
variable proportion of water. The soil contains clay
and sand (silica), lime, iron, potash, phosphorus,
sulphur, ammoniacal salts, and other matters which
are of no importance. Thus, between them, the soil
and the atmosphere contain all the elementary bodies
which we find in the plant : but the plant has to
separate tliem and join them together afresh,

90 SCIENCE PRIMERS. [material

Moreover, the new matter, by the addition of which
the plant grows, is not applied to its outer surface, but
is manufactured in its interior; and the new molecules
are diffused among the old ones.

62. The Living Plant, after it has grown
up, detaches part of its Substance, which
has the Power of developing into a similar
Plant, as a Seed.

The grain of wheat is a part of the flower of the
wheat plant, which, when it becomes ripe, is easily
separated. It contains a minute and rudimentary
plant; and, when it is sown, this gradually grows, or
becomes developed into, the perfect plant, with its
stem, roots, leaves and flowers, which again give rise
to similar seeds. No mineral body runs through a
regular series of changes of form and size and then
gives off parts of its substance which take the same
course. Mineral bodies present no such develop-
ment and give off no seeds or germs. They do not
reproduce their kind.

^2,. The Living Animal increases in Size by
adding to the Substances which compose its
Body, like Substances ; these, however, are
chiefly derived directly from other Animals
or from Plants.

The fowl in the farm-yard is incessantly pecking
about and swallowing now a grain of corn, and now
a fly or a worm. In fact, it is feeding, and, as every
one knows, would soon die if not supplied with food.
It is also a matter of every day knowledge that it
would not be of much use to give a fowl the soil of
a corn-field, with plenty of air and water, to eat.

OBJECTS.] INTRODUCTORY. qt

In this respect, the fowl is like all other animals ; it
cannot manufacture the proteid materials of its body,
but it has to take them ready made, or in a con-
dition which requires but very slight modification, by
devouring the bodies either of other animals or of
plants. The animal or vegetable substances devoured
are taken into the animal's stomach; they are there
digested or dissolved; and thus they are fitted to be
distributed to all parts of the fowl's own body, and
applied to its maintenance and growth.

64. The Living Animal, after it has grown
up, detaches part of its Substance, which has
the Power of growing into a similar Animal,
as an Egg.

The fowl's egg is formed in the body of the hen,
and is, in fact, part of her body inclosed in a shell
and detached. It contains a minute rudiment of a
fowl; and when it is kept at a proper temperature
by the hen's sitting upon it, or otherwise, for three
weeks, this rudiment grows or develops, at the
expense of the materials contained in the yolk and
the white, into a small bird, the chick, which is then
hatched and grows into a fowl. The animal, there-
fore, is produced by the development of a germ in
tlie same way as the plant; and, in this respect, all
l)lants and all animals agree with one another and
differ from all mineral matter.

65. Living Bodies differ from Mineral
Bodies in their Essential Composition, in
the manner of their Growth, and in the fact
that they are reproduced by Germs.

Thus there is a very broa4 distinction between

Q2 SCIENCE PRIMERS. [immaterial

mineral matter and living matter. The elements of
living matter are identical with those of mineral
bodies; and the fundamental laws of matter and
motion apply as much to living matter as to mineral
matter; but every living body is, as it were, a com-
plicated piece of mechanism which "goes," or lives,
only under certain conditions. The germ contained
in the fowl's egg requires nothing but a supply of
warmth, within certain narrow limits of temperature,
to build the molecules of the egg into the body of
the chick. And the process of development of the
egg, like that of the seed, is neither more nor less
mysterious than that, in virtue of which, the mole«
cules of water, when it is cooled down to the freezing-
point, build themselves up into regular crystals.

The further study of living bodies leads to the
province of Biology, of which there are two great
divisions — Botany, which deals with plants, and
Zoology, which treats of animals.

Each of these divisions has its subdivisions — such
as Morphology, which treats of the form, structure,
and development of living beings, and Physiology,
v/hich explains their actions or functions, besides
others.

m. IMMATERIAL OBJECTS.

66. Mental Phenomena.

Material objects are all either not living, that is to
say, mineral bodies, or they are living bodies. Every-
thing which occupies space, offers resistance, has
y/eight and transfers motion, belongs to pne or

I

OBJECTS.] iMTRODUCtORY. 93

other of these two great provinces of nature. The
sciences of Astronomy, Mineralogy, Physics, and
Chemistry deal with the former, while Biology, with
its two divisions of Zoology and Botany, treats of
the latter. But natural knowledge is not exhausted
by this catalogue of its topics. In the very first para-
graph of this Primer, in fact, we had occasion to
draw a distinction between Things, or material ob-
jects, and Sensations ; and a moment's reflection
is sufficient to convince you that sensations are not
material objects. A smell takes up no space and has
no weight ; and to speak of a pound or of a cubic
foot of sound, or of brightness, is, on the face of the
matter, an absurdity. Pleasure is said metaphorically
to be fugitive, but you cannot imagine a pleasure as
a thing in motion.

What we call our Emotions are in like manner
devoid of all the characters of material bodies. Love
and hatred, for example, cannot for a moment be con-
ceived to have shape, or weight, or momentum. And
when, in reasoning, we think, our Thoughts have
the same lack of the qualities of material things.

Sensations, emotions, and thoughts, thus constitute
a peculiar group of natural phenomena, which are
termed mental.

67 The order of Mental Phenomena : Psy-
chology.

A definite order obtains among mental phenomena,
just as among material phenomena ; and there is no
more chance, nor any accident, nor uncaused event, in
the one series than there is in the other. Moreover,
there is a connection of cause and effect between

04 SCIENCE PRIMERS. Timmaterial

^ L OBJECTS.

certain material phenomena and certain mental phe-
nomena. Thus, for example, certain sensations are
always produced by the influence of particular ma-
terial bodies on our organs of sense. The prick of
a pin gives pain, feathers feel soft, chalk looks white,
and so on. The study of mental phenomena, of the
order in which they succeed one another, and of the
relations of cause and effect which obtain between
them and material phenomena, is the province of the
science of Psychology.

All the phenomena of nature are either material
or immaterial, physical or mental ; and there is no
science, except such as consists in the knowledge of
one or other of these groups of natural objects, and
of the relations which obtain between then\

l-HE END.