The Road To Modern Science

TEXT CROSS
WITHIN THE
BOOK ONLY

166550

THE ROAD
TO MODERN SCIENCE

The Road
To Modern Science

By
H. A. REASON, B.Sc.

LONDON

G. BELL & SONS, LTD
1935

Tot
W. R. and K. R.

Printed in Great Britain by
NEILL & Co., LTD.,

FOREWORD

THE primary object in writing this book was to present
the story of scientific discovery in a form which would
appeal to intelligent boys and girls. The subject-matter
of the majority of the books on the history of science is,
in the main, too difficult for such readers. On the other
hand, in those books which tell only the story of the
lives of a few great scientists, the broad view of scientific
discovery, as a whole, tends to be obscured.

While the audience I have had in mind has, therefore,
been youthful, I hope very much that this book may also
appeal to more adult readers for whom the scientific
achievements of this modern world have not lost all
their wonder, and who may like to read the story of
what went before.

I should like to thank Miss C. M. Waters, B.A., and
Miss E. C. Underwood, B.A., for much helpful advice
and criticism of the text.

CONTENTS

PAGE

LIST OF PLATES ...... viii

PART I

CHAP.

I. THE TRAIL BEGINS ..... i

II. THROUGH THE ANCIENT WORLD ... 5

III. INTO A NEW WORLD ..... 15

IV. ARISTOTLE ....... 21

V. SCIENCE IN ALEXANDRIA .... 27

VI. THROUGH THE DARK AGES 35

VII. THE DAWN OF A NEW AGE .... 48

VIII. GALILEO 58

IX. NEWTON, THE MASTER BUILDER ... 66

PART II

X. CHEMISTRY ....... 77

XL MAGNETISM AND ELECTRICITY . . .no

XII. THE DEVELOPMENT OF POWER . . . 146

XIII. WAVES OF MANY KINDS .... 168

XIV. ASTRONOMY ....... 197

XV. BIOLOGY 220

XVI. THE MODERN ROAD 263

SUMMARIES OF PART II 274

INDEX 297

Vll

LIST OF PLATES

Plate

I. ARCHIMEDES and PARACELSUS . . . page 32

II. AN ALCHEMIST AT WORK .... ,, 48

III. LEONARDO DA VINCI and COPERNICUS . ,, 49

IV. TVCHO BRAHB ,, 65

V. GALILEO and GALILEO'S TELESCOPE . ,, 70

VI. SIR ISAAC NEWTON . . . ,, 71

VII. THE HON. ROBERT BOYLE ... ,, 77

VIII. DR JOSEPH BLACK and THE HON. HENRY

CAVENDISH T* ,, 86

IX. DR JOSEPH PRIESTLEY and HIS PNEUMATIC

TROUGH ...... ,, 87

X. LAVOISIER IN HIS LABORATORY ... ,, 97

XI. DR GILBERT SHOWING HIS ELECTRICAL EX-
PERIMENTS TO QUEEN ELIZABETH AND HER
COURT ...... 120

XII. BENJAMIN FRANKLIN and PRIESTLEY'S ELEC-
TRICAL MACHINE . . . . . ,, 121

XIII. MICHAEL FARADAY . . . . . ,, 136

XIV. FARADAY IN HIS LABORATORY AT THE ROYAL

INSTITUTION . . . . . ,, 137

XV. GUERICKB'S FIRST EXPERIMENT (THE MAGDE-
BURG HEMISPHERES) . . . . ,, 152

XVI. GUERICKB'S SECOND EXPERIMENT TO SHOW THE

PRESSURE OF THE ATMOSPHERE and JAMES

WATT ,, 153

XVII. SIR HUMPHRY DAVY . . . . ,, 177

XVIII. HERSCHEL'S GIANT TELESCOPE and A SPIRAL

NEBULA ,, 192

viii

LIST OF PLATES ix
Plate

XIX. AN ILLUSTRATION FROM VfiSALIUS* BOOK ON

ANATOMY ...... page 224

XX. ONE OF LEEUWENHOEK'S MICROSCOPES and

SOME FOSSILS . . . . . 240

XXI. Louis PASTEUR and LORD LISTER . . 241

XXII. CHARLES DARWIN ,, 257

XXIII. MME CURIE and PROFESSOR EINSTEIN . ,, 264

XXIV. LORD RUTHERFORD . . . . . ,, 265

Illustrated Time- Charts will be found at the beginning
and end of the book.

PART I

CHAPTER I

The Trail Begins

MANY trails have been blazed since man first made his
appearance on earth some hundreds of thousand years
ago. Some of these have petered out long ago; others
have merged together into wide roads which have run
through the centuries and are now the main thorough-
fares of our modern life. The trail which we are going
to follow in this book has become perhaps the widest and
most important of all others during the last three cen-
turies. I mean the great Highroad of Modern Science.
The road is still being made, wide and straight and filled
with traffic. Some of the wise people who are watching
its progress are asking * Where will it lead to a good
end or to a bad ? ' That is a question that not only the
makers but the users of the road must consider.
^ Now what really is Science? The word 'science'
means * knowledge,' so that in its broadest sense it means
all the knowledge that man has gained, arranged in an
orderly manner. Thus everything that you learn in
school is really Science. We generally use the word,
however, with the more limited meaning of our know-
ledge and understanding of the world around us as it is
shown to us through our various senses. Notice that
knowledge can only be called c science ' when it is orderly.
Man gained a great deal of knowledge before he began to
think about it as 'knowledge'; that is, to arrange and

2 THE ROAD TO MODERN .SCIENCE

classify it, to notice similarities and differences between
various parts and so to make ' general statements.'

Now imagine that you do not live in the twentieth
century but far back in prehistoric times. You are
really almost an animal, but you are not quite, because
you have a better brain than an animal, one which has
the power to ' reason,' though only in a very elementary
fashion. You have also a much more definite memory
than an animal. You probably live in a cave with a tribe
of other prehistoric people like yourself and you have to
hunt for your food and protect yourself from other
animals. That is your main business in life. Now
because you have a better memory and because you can
reason things out a little, you make a rather better
business of living than the animals. You gradually rely
more and more on your brain and less on your physical
powers in order to escape the big animals and to kill the
others for food. You find, for instance, that you can
make a weapon out of a flint at the end of a wooden
pole, which can do more harm than your teeth or claws,
and which, at the same time, can keep you more out of
range of the animal you are fighting. So gradually you
accumulate a great many bits of knowledge that are very
useful to you in your business of living. But each bit is
quite separate from every other bit, and you only think of
it as applying to the particular circumstances in which
you first learnt it.

Two of the most important things that happened
to primitive man were his beginning to talk and his
beginning to count. The latter probably happened very
much later than the first, and it is with this event that our
trail really begins. Let us try to imagine how it happened.

At first, a prehistoric man fishing for his family would

THE TRAIL BEGINS 3

go on fishing until each of the, say, five of them had a
fish; but he could not go down to the river and catch
' five fish ' unless his family were there to be given them
in turn, until each had one. Later he learnt to count
'five fishes' or 'five stones/ but saw no connection
between the two. Finally, however, on one of his
descendants this connection dawned, and he realised that
one, two, three, five, etc., had a meaning apart from the
fishes or stones to which they had always been attached.
That man, whoever he may have been, was the first
pioneer to start blazing the trail which was to wind, now
clear, now faint, now broad and straight, now narrow
and tortuous, till the great giants of the sixteenth century
tracked their way through the undergrowth which had
grown up and made our modern high road. As we look
back upon the makers of the road we see that perhaps
the most useful tool they had for their task was this
knowledge of counting and number, which was first
fashioned* crudely and roughly, by our unknown pre-
historic man.

For many thousands of years man went on accumu-
lating knowledge and using it for his business of living,
He stopped living in small tribes and built himself cities
and lived in large communities. In other words, he
gradually became civilised. He still, however, only used
his knowledge for the practical business of living and
enjoying life. He had all sorts of luxuries; he learnt
how to hand on his knowledge by writing; but every-
thing he learnt or did had a practical end in view. He
never found out things just for the sake of knowing them.
The first people to pursue knowledge for its own sake
were the Greeks, and with them ' Science ' really has its
origin. But in the efforts of the Greeks to bring all the

4 THE ROAD TO MODERN SCIENCE

knowledge that man possessed into one big orderly whole,
they had, to help them, all the knowledge gained by the
men who had lived on the earth before their time. Thus,
although it is only when we reach the Grecian Era that
we find the signpost 'Science,' the trail is to be found if
we look for it, winding from our prehistoric man through
the time of the ancient civilisations to the foot of the
signpost.

CHAPTER II

Through the Ancient World

THERE were three great races of people from whom the
Greeks learnt their knowledge. They were the Egyptians,
the Babylonians, and the Phoenicians ; and they were all
in a flourishing state during the years 1000 B.C. to 500 B.C.,
during which time the Greeks were gradually winning
for themselves a strong position on the north-east coast
and islands of the Mediterranean Sea. Let us see just
what kind of a life these three nations lived at that time
and what was the most important contribution of each
to the knowledge which was the heritage of the Greeks.

The Egyptians. The civilisation of the Egyptians is
one of the oldest civilisations on the earth. These people
lived on the banks of the Nile and the small strip of fertile
country on either side. This fertile land they cultivated,
and grew there a great many crops of much the same kind
that we grow nowadays. Besides food-crops, they also
grew flax, and, from the thread spun from this, they wove
themselves linen garments and dyed them many beautiful
colours from dyes which they learnt to make. They also
grew the Papyrus grass, from which they made paper to
write on, and thus left records of their doings which people
living afterwards have found and read.

Now every year the Nile floods its banks because of the
tropical rains which fall in the region where the river
rises. This makes the land round it very fertile, but it
also meant, at that time, that every year the fields on its
banks had all their boundaries wiped out, so that the

5

6 THE ROAD TO MODERN SCIENCE

land had all to be divided out again when the floods
subsided. It was, therefore, very necessary for the
Egyptians to have some way of measuring up the land, in
order that after the flood each should have his right
amount again. The land was measured out in rectangles,
and a tax was paid to the King on each rectangle of a
certain size. Now it was easy enough to measure the
lengths of the sides of the rectangles, but it was not so
easy to make the angles between the sides really right

FIG. i

Angles. Remember that there were no protractors and
geometry had never been heard of. However, the
Egyptians discovered, practically, a very important bit
of knowledge, which was, that if a rope of twelve units in
length is divided by knots into sections of three, four,
and five units and made into a triangle with the knots at
the corners, then the angle opposite the side of five units
is always a right angle. This is a special case of one of the
theorems in geometry, but the Egyptians only knew it as
a fact of experience, and, as far as we know, did not
bother their heads as to 'why/ It was not until a long
while later that a Greek, named Pythagoras, whom we

THROUGH THE ANCIENT WORLD 7

shall talk about again, realised that other lengths for the
sections would also give a right angle provided that the
lengths are related to each other in the special manner
demonstrated in Pythagoras' theorem. Pythagoras was
a scientist , but the Egyptian 'rope-stretchers,' as the land-
measurers were called, were not.

The buildings of the Egyptians also show that they
had great skill in practical measurement and construction,
and their * right-angle device* was used in building and
orientating their temples. The most famous of their
buildings were the great Pyramids or tombs in which
they buried their kings. The fact that they have lasted
about four thousand years shows how well they must
have been built. These Pyramids, when measured
to-day, are found to be very accurately constructed.
The angles at the base are all almost exactly 52. The
Egyptians, of course, had no machines, and yet they
were able to lift the great masses of stone of which the
Pyramids were made to a height of 500 ft., higher than
the cross on top of St Paul's Cathedral. This they did
by means of ropes, pulled by a great army of slaves, and
possibly by the aid of levers ; but you must realise that
they knew nothing about the * lever law' which was
discovered much later by another Greek, Archimedes.

One of the things which the Egyptians were the first
to do was to invent a calendar. The earliest known
date in human history is 4241 B.C., when the Egyptian
calendar was invented. The man who devised this
calendar knew that the sun took three hundred and
sixty-five days to complete the circle of the seasons ; and
that the moon went round the earth in twenty-eight days.
This shows that the Egyptians must have watched the
movements of the sun and moon very carefully. Their

8 THE ROAD TO MODERN SCIENCE

records also tell us that they watched the stars as well,
calling certain of them by definite names and picking out
groups of them which seemed to form pictures. These
are what we now call the constellations, and our names
J[or them mean the same as did the old Egyptian names.

The Egyptians did not just stay quietly in their lands
on the banks of the Nile. They built themselves ships,
and in these they ventured down the Nile into the Medi-
terranean; and, by cutting the first Suez Canal, they
sailed through to the Red Sea. In this way they traded
with, and at one time conquered, other civilised nations,
and later on were in their turn conquered. So they
obtained more knowledge, not by discovery for themselves,
but by copying what they saw being done by those other
nations.

The Babylonians. The chief race of people with whom
the Egyptians came in contact were the Babylonians
who inhabited the land between the Euphrates and the
Tigris, which we now call Mesopotamia. In most ways
the civilisation of the people dwelling in Mesopotamia
was very much the same as that of the Egyptians. They
cultivated the land ; wove and embroidered their clothes ;
built themselves cities and palaces ; and made laws which
they wrote down, so that we find them to-day.

Babylonia was not quite so fertile a land as Egypt, nor
was the climate quite so good. To water the land away
from the river they therefore built canals, and so were
the first people to use irrigation. Again, unlike the
Egyptians, they had not great quantities of building
stone in their land. Instead, they made bricks out of
clay and baked them in the summer sun. These bricks
were not as lasting as stone, and so we do not find their
buildings still standing entire to-day.

THROUGH THE ANCIENT WORLD 9

They also used clay to make tablets on which to write.
They probably began by picture writing, using a reed to
mark the clay; but this did not make good pictures, so
that they soon took to using symbols, something like
this Y-<- Whole libraries of these tablets have been
found, and these tell us a great deal about the life of the
Babylonians. They were quite good at counting, and at
arithmetic, but they did not usually count in tens, as we
do, but in sixties. Thus, suppose that (in their writing)
they wrote a number such as 16; the i would not stand
for ten but for sixty, and the number would therefore be
sixty-six not sixteen. Our division of the hour into
sixty minutes, and the minute into sixty seconds, dates
right back to the days of Babylon.

Amongst the things which have been dug out of the
ground in the land of the Babylonians are a number of
very beautifully worked chains and vessels in gold, silver,
and bronze. We know, therefore, that they must have
had very skilled metal-workers amongst them. Now
the discovery of metals, and of how to use them for
making weapons and vessels, was one of the most im-
portant discoveries in the history of man. At first, as
you know, man made himself weapons of flint and stone.
Copper was probably discovered by the Egyptians first.
Perhaps some Egyptian traveller on the Sinai peninsula
made a fire and built it round with bits of rock which he
found lying about. In the morning, when he raked out
the fire, he found among the ashes hard shiny, red beads
of copper. What had happened? Nowadays, we get a
very great number of metals out of the ground and use
them for all sorts of purposes, but only a very few of them
look like metals when they are in the ground. Before
they can be used, the rocks containing them have to be

io THE ROAD TO MODERN SCIENCE

treated in some way, and nearly always, at some stage,
they have to be heated with carbon either as coke or char-
coal. This process is known as smelting. Now you will
see how that old Egyptian got his copper. The hot
charcoal from his fire acted on the rocks surrounding it
and produced the metal copper. At first he probably
only used these metal beads as ornaments, but when he
discovered how hard they were he would try to get more
with which to make weapons or vessels.

Now copper melts at a considerably lower temperature
than a metal such as iron, and so it was quite easy to melt
the copper and so to make it into any shape that was
wanted. It can also be won from the rock containing it,
at a much lower temperature than iron, and that is prob-
ably why it was discovered so long before. Gold, silver,
and tin were discovered somewhere about the same time as
copper, but gold and silver are too soft to be of very much
use by themselves for anything but ornament. A method
of hardening copper still further was discovered when the
metal had been in use sometime under a thousand years.
This was done by melting a little tin with the copper and
making the alloy known as bronze. For very many years
this was the hardest and strongest substance known, and
all weapons were made of it. From the many articles of
bronze, copper, gold, and silver that have been found in
Babylonia, it is clear that the old inhabitants of that land
must have been greatly skilled in all kinds of metal work.

I have left it until the last to tell you about that thing
for which the Babylonians are most famous : that is their
study of the stars. They seemed to have noticed that
things on earth began to grow when the sun, at midday,
was a certain height in the sky. They saw, also, other
changes on the earth, and noticed changes in the moon

THROUGH THE ANCIENT WORLD 11

and stars occurring at the same time. From this the idea
grew up that the sun, moon, and stars really controlled
the happenings on earth. It therefore seemed to them
very important to study the changes in these heavenly
bodies, so that they might glean from them some informa-
tion as to what was likely to happen on earth. Accord-
ingly, their wisest men spent their lives in watching the
sky, recording all changes and making star-maps. The
magi of the Bible were probably three of these wise men
of Babylonia. Notice that they did not study the stars
just for the sake of knowing about them, but because they
thought that from their changes they could foretell future
events on the earth. These men were what are known
as Astrologers, while the men of to-day who study the
stars, for the sake of knowledge alone, are called Astron-
omers. Nevertheless, the records of these old Babylonian
astrologers have been very useful to later astronomers,
because most of the changes in the sky are very slow, and
so it is of great value to have records of what the sky
looked like thousands of years ago.

The Babylonian astrologers picked out the five planets :
Mercury, Venus, Mars, Jupiter, and Saturn; and these
five * wandering stars/ with the sun and the moon, were
supposed to play an extremely important part in the lives
of men. Like the Egyptians, they had also names for
various constellations or groups of stars. Now, each
day the sun at noon occupies a slightly different position
among the stars, and during the year it apparently traces
out a huge circle in the heavens. The constellations
which lie on this circle were supposed to be of especial
importance, and the representations of them are still
known as the signs of the Zodiac.

From their observations of the sun in its course across

12

THE ROAD TO MODERN SCIENCE

the sky, the Babylonians made the first clock. It was
known as a water-clock or clepsydra. They allowed
water to drip regularly from a large vessel, and the moment
the sun's upper rim began to appear above the horizon

FIG. 2

they began to collect it. Directly the whole of the sun
was above the horizon they changed the vessel and went
on collecting until the sun just began to appear above
the horizon next day. By dividing the water into equal
parts they thus had a means of dividing the day into equal
parts and so first began to reckon timfe.

The Phoenicians. At the time of the rise of Greece the
Phoenicians were the great traders of the world. They
were only a small nation, and from some points of view

THROUGH THE ANCIENT WORLD 13

might not be considered so worthy of mention as other
small nations existing at that time. It is because of the
great part they played in spreading knowledge that I am
mentioning them here.

The Phoenicians lived on the narrow fertile strip on tKe
west of Asia Minor, just north of Palestine. In their
country were the famous cedars of Lebanon, and from
these trees they built themselves ships and traded all
round the Mediterranean, even through the Straits of
Gibraltar and round the coast of Spain as far as Cornwall.
On the mountains behind their coast they reared sheep,
and from the wool wove cloth. They were especially
clever at making dyes and with these they dyed the cloth
they wove.

The important discovery of how to make glass is some-
times attributed to the Phoenicians. They certainly knew
how to make it and traded in it with the countries they
visited. The story goes that some Phoenician sailors
making a fire on a sandy shore, built the fire round with
bits of stone which probably contained lime and natron
(soda). On raking the ashes they found not copper this
time, but glass ; for lime, soda, and sand are what we now
use to make glass. As a matter of fact, glass was probably
made for the first time long before the time of the Phoeni-
cians, but that is very likely the way in which it was first
made.

The Phoenicians also became very expert metal-workers,
and this was perhaps the basis of their most important
trade with the more uncivilised parts of western Europe.
They guarded the secret of their skill very jealously,
however, and would only hand on the lore to their own
race. Many of them settled in different parts of Europe
and became the smiths of the countryside. Cornwall,

14 THE ROAD TO MODERN SCIENCE

being so rich in mineral wealth, soon had a Phoenician
smith to almost every tribe, and to-day, if you go to Corn-
wall, you may meet people who proudly claim to be
descended from the Phoenicians.

Let us now take a wide view at the world about 1000 B.C.
and during the next few centuries. Asia was the centre of
civilisation. Almost all of the southern part of that
continent * was inhabited by civilised people that is, by
people who had, to a great extent, learnt how to control
the natural world around them and to live a life in which
there was room for leisure. There was intercourse of trade
and war between the various nations, and in both ways
knowledge was spread amongst the peoples. But every-
where we see this knowledge being applied to practical
purposes and being valued only for the part it played in
contributing to the safety and comfort of man. As more
knowledge was accumulated, so the people grew in luxury
and wealth. But no new ground was broken, and super-
stition prevented any step forward. These were not the
people who were to strike out into the unknown and blaze
new trails in search of greater things.

1 I have not especially mentioned India and China here not
because they were not important centres of civilisation at that time,
but because the paths of knowledge made by them never joined up
with the path which eventually led to our modern high road of science.

CHAPTER III

Into a New World

WE have already seen that copper was discovered and used
a long time before iron. The discovery of the latter and
of how to weld it into weapons happened somewhere
about 1 200 B.C. About this time a new race of people
settled on the shores of the ^Egean Sea in the land known
to them as Hellas, but to us now as Greece. It has been
suggested that these people were greatly helped in the
conquest of the inhabitants of that country by the use of
weapons made of the new metal, iron. Whether or not
the Greeks did thus truly usher in the 'Iron Age,' it is
quite certain that they brought to the civilisation round
the Mediterranean Sea a new age of the mind the Age of
Science, of the desire to understand and to explain every-
thing that they saw happening round about them.

Until about 700 B.C. the Hellenes were occupied in
establishing themselves in the land, and fighting, one state
with another. By this date, however, a number of
prosperous city states had been established, and most of
the islands in the ^Egean Sea had been colonised. Of
these island colonists the lonians are particularly famous,
and to them belonged Thales, the first of the long line of
Greek philosophers or 'seekers after the ultimate truth.'

Thales. Thales was born in Miletus in 624 B.C. Like
many of his countrymen he was originally a prosperous
merchant and traded chiefly in salt and oil. In this way
his business took him abroad a great deal, and especially
to Egypt. Now while in that country he became very

is

16 THE ROAD TO MODERN SCIENCE

much interested in the practical knowledge of the
Egyptians, more especially in their methods of land
measurement, and in their observations of the stars.
He therefore collected a$ much information as he could,
and when he got home he gave up his business as a
merchant and devoted the rest of his life to 'philosophy.'
One of the first things he realised about the Egyptian
rules for land measurement was that they were only
special cases of much more general rules. These ' general
rules* which he stated were the true beginnings of the
science of geometry. One particular theorem which
Thales stated and proved was the one about angles at the
base of an isosceles triangle always being equal. Once
started on geometry the Greeks took to it like ducks to
water, and there is very little of 'the geometry learnt at
school which did not originate from them.

Another interesting thing to note about Thales is that,
as far as we know, he was responsible for the very begin-
ning of our knowledge of electricity. He found that when
amber is rubbed it can attract small light things to it, or,
as we now say, it becomes electrified. Now the Greek
word for amber is 'electron/ and so all our words of that
root can be traced back to Thales and his experiments
with amber. He also possessed a bit of lodestone, which
is a naturally occurring magnet, and he found out many
Df its properties.

Perhaps the most important thing of all to remember
about Thales is that he was one of the very first men to
ask the question: 'What is everything made of?' This
question was, perhaps, more discussed than any other by
Greek philosophers. Although a variety of answers were
given, it was fairly unanimously agreed that the different
things found round about them were made up from just

INTO A NEW WORLD 17

a few simple substances which were called 'elements.'
Thales himself said that all things were originally pro-
duced from water. Now, it is very interesting to note
that, at the present time, scientists have come back to the
old Greek idea that all matter is really made up from one
elementary substance. We know now that Thales was
quite wrong in thinking that substance to be water, but
in one way he was nearer the truth than were our scientists
some sixty years ago when they thought that there were
about seventy or eighty different kinds of elements with
nothing common to them all.

Thales, as well as studying philosophy, on his own
account, also taught his conclusions to others. Some of
these themselves made important contributions to the
knowledge of their day, and in their turn had pupils of
their own. In this way the love of philosophy spread,
and everywhere through Greece we find men questioning
and seeking explanations of all that they saw about them.
Here, indeed, was a race of road-makers, continually
breaking fresh ground and pressing on into the unknown.
We can only mention one or two of the most famous of
the Greek philosophers, and only those who were most
interested in what we now call Science. The next one
we shall take is one whom we have already mentioned,
namely, Pythagoras.

Pythagoras. Pythagoras was also an Ionian and was
born in the island of Samos in 580 B.C. Like Thales he
travelled to Egypt and also perhaps to Babylon, and thus
became familiar with the ways of the people of those lands.
On his return he settled in southern Italy, which by that
time had become a Greek colony. Here he became
famous. Many people came to learn from him and a kind
of brotherhood was formed. Before joining the brother-

i8 THE ROAD TO MODERN SCIENCE

hood everyone had to take certain vows, some of which
were definitely religious. All vowed to live a simple and
austere life. It is interesting to find that women were
admitted to this brotherhood, and the wife of Pythagoras
was an important member.

We, however, are only concerned with the contributions
of Pythagoras to Science. We have already attributed
the beginning of geometry to Thales, but Pythagoras is
definitely the founder of the Science of mathematics as
a whole. He was more interested in c numbers ' than in
anything else, and he thought that the numbers connected
with any object were the most essential part of it. * Ten '
he called the perfect number, because 10 = 1+2 + 34-4.
' Three ' was the sacred number ; it was the number of the
universe, because everything has its beginning, its middle,
and its end. If you think of the well-known theorem of
Pythagoras you will remember that it is the theorem
where numbers play the most important part. Since he
was so fond of numbers you will not be surprised to hear
that Pythagoras first introduced a proper system of weights
and measures.

The study of the theory of sound was first begun by
Pythagoras. The story goes that one day, while passing
a blacksmith's shop, he was attracted by the musical notes
emitted by the anvil on being struck by the hammer.
This led him to investigate the notes produced by strings
of various lengths and thickness, and he found that if he
had two similar strings, but one twice as long as the other,
the short one produced a note which was an octave higher
than the other. If the ratio of the lengths was 3 : 2 the
interval was a fifth, while with lengths of 4 : 3 a fourth was
produced. Again he got back to his magical series one,
two, three, four, and the idea of harmony and proportion

INTO A NEW WORLD 19

in everything. Following up the same idea, he pictured
the universe as having a central fire around which the sun,
the earth, and the planets revolved with varying speeds,
each creating its own celestial note, according to its
distance from the central fire, and all together giving rise
to the * music of the spheres.'

Like Thales, Pythagoras sought an answer to the
question of the structure of matter. He, however, held
the theory that all matter was made, in varying proportions
of four elements earth, air, fire, and water. This is
known as the famous 'four element* theory which held
sway until the end of the Middle Ages. The teachings of
Pythagoras had more influence than those of Thales, and,
in fact, were only eclipsed by those of the great Aristotle
himself.

Hippocrates of Cos. Before we come to Aristotle there
is one other Greek philosopher whom we must mention.
This is Hippocrates, known as the 'Father of Medicine/
He was born in the island of Cos in 460 B.C. Like Thales
and Pythagoras he travelled extensively over the countries
bordering the eastern Mediterranean.

Up to this time, if a man were ill it was thought to be an
infliction of the Gods, and that the only remedy was to
appease them by offering sacrifices. Thus the chief
people concerned in the healing of sickness were the
priests of the temples. Now, Hippocrates taught that
sickness was due to something wrong in the working of
the body, and not to an external cause such as the dis-
pleasure of the Gods. To be able to cure the disease, he
said, one must study the patient and find out what is
causing the trouble. This, of course, is just what doctors
of to-day try to do. Hipocrates' theory was that there
were in the body four hujovpirs or juices blood, phlegm,

20 THE ROAD TO MODERN SCIENCE

yellow bile, and black bile. When these were present in
the right proportions and properly mixed, then the body
\vas healthy ; but if the proportions were incorrect, then
illness resulted. Now, although this is now known not
to be the true explanation, it was the one held by all
doctors until about four hundred years ago, and it
certainly was nearer the truth than the supernatural one
believed up till then.

Hippocrates was the first to propound what is, nowa-
days, a very favourite maxim : * Nature is the best of all
healers ' ; and his chief method of cure was a regulation of
diet. So Hippocrates thus well deserved the title ' Father
of Medicine/ and it is most interesting to know that the
oath which was taken by his pupils before they were
allowed to practise medicine is still taken in much the
same form by medical students to-day who are about to
become doctors.

CHAPTER IV

Aristotle

WE now come to the two greatest names among all the
Greek Philosophers, Plato and his pupil Aristotle. Plato
himself was a pupil of another, the famous Socrates, of
whom you have probably heard; and Aristotle, in his
turn, was tutor to Alexander the Great. So we have a
chain of four great personalities linked together ; and the
interesting thing is that they are all quite different. From
the point of view of science, Aristotle is far the most
important of the four.

Plato. Plato, who lived between the years 427 and
347 B.C., founded a very famous school in Athens known
as the Academy. It stood in a pleasant grove with shady
walks, and over the door was written the inscription:
'Let no one ignorant of Geometry enter here.' This
would lead you to think that Plato must have been a true
follower of Pythagoras, but this was not the case; for he
thought that to apply geometry to practical purposes,
such as making instruments, was degrading it. Geo-
metry, he said, was a means of withdrawing the mind from
material things and concentrating them on the abstract.
Thinking, in this way, on geometrical figures he came to
the conclusion that the circle was the most perfect curve
in nature, and that therefore the paths of the various
heavenly bodies must be in circles. Now, Plato was such
a great man that his teachings were implicitly believed,
not only by all the Greeks who lived after him but by all
the people of western Europe for many hundreds of years.

22 THE ROAD TO MODERN SCIENCE

So that, when a man named Kepler, who was a friend of
Galileo, nearly two thousand years later, showed by
observation and calculation that most of the planets did
not travel in circles but ellipses, very few people, at the
time, were disposed to believe him.

Plato was not really very much interested in the
natural world about him. He was far more interested in
Man and in the way in which he ought to behave ; or, to
use the proper word, he was interested in Ethics. His
use for geometry was, therefore, to teach his students to
think clearly and reason logically.

Aristotle. To Plato's Academy, when he was eighteen
years old, came an enthusiastic, energetic young man
named Aristotle. Aristotle was born in Stagira in 384 B.C.
and was the son of a physician. He had, therefore, been
brought up amid circumstances which had created an
interest in medicine and biology, and this persisted even
when under such different influences as at the Academy.
He worked so hard that he quickly became one of Plato's
best pupils. He is said to have reduced the hours spent
in sleep to a minimum. When he was reading in bed at
night he placed beside him a brass basin, over which he
held in his hand a leaden weight. When he was over-
come with sleep, the weight dropped from his inert hand
and the sound of its fall into the basin awakened him. It
is not altogether surprising that a man of such persistent
and untiring energy should have exercised such an in-
fluence over the thoughts of mankind for so many
hundreds of years.

Aristotle stayed at the Academy until Plato died in
347 B.C. He then left Athens and shortly afterwards
became tutor to the young Prince Alexander, son of King
Philip of Macedonia. When Alexander became king

ARISTOTLE 23

Aristotle returned to Athens and started a school of his
own, which was called the Lyceum. At the entrance to
the building was a covered portico or 'peripatos,' from
which led a gravel walk between an avenue of trees. Here
Aristotle used to walk up and down with his pupils, dis-
cussing various problems and teaching as he went.
Because of this, his school became known as the Peri-
patetic school, and his followers were known as the
Peripatetic philosophers.

It was at this famous school that, during the next twelve
years, Aristotle gave himself up entirely to what he con-
sidered his ' life-work.' This, very briefly, was to write
a catalogue or compendium of the knowledge of all
natural phenomena. Up till then the various great men
who had found out things and taught their knowledge to
others had done so chiefly by word of mouth, and only
fragments of their teachings had been preserved in writing.
It is, of course, chiefly because of the fact that Aristotle
wrote dowa so much that his teachings had so much in-
fluence for such a long time.

Aristotle's method of setting about things was this:
First of all, he collected as many ' facts ' as he could about
every kind of subject he could think of animals, fishes,
plants; moving bodies; different kinds of matter; the
phenomena of burning; the $tars and heavenly bodies,
and so on and so forth. Then he classified them into
groups and under various heads; and finally he made
theories as to why things happened as they did and were
as he found them, reasoning always about things in the
proper logical way which he had learned from Plato.

All this sounds very excellent, and yet Aristotle was one
of the greatest stumbling-blocks in the way of later great
scientists such as Galileo, How did this come to be so ?

24 THE ROAD TO MODERN SCIENCE

The explanation is this. Aristotle's reasoning was all
right he is still admitted to be one of the greatest ex-
ponents of logic but in so many cases his 'facts' were
wrong. He did not trouble enough to test his facts for
himself, but either believed tales which were told him or
assumed that things happened in a way in which they
really did not. Perhaps the most famous example of a
wrong fact is the one over which Galileo fought his
famous battle with the professors of Pisa. Aristotle had
taught that heavy bodies fall as many times faster than
small bodies as they are heavier. Galileo, in front of all
the professors, dropped a heavy weight and a light weight
from the top of Pisa's leaning tower, and behold, they both
reached the ground together! Now, although the pro-
fessors did not even then really believe their own eyes, but
still clung blindly to the teachings of Aristotle, yet I think
we must allow that had Aristotle been there he would
have at once given way to Galileo over the matter. The
trouble with him was that he never thought of trying the
experiment for himself. This applies to nearly all his
teachings in the branch of Science which we now call
Physics ; and since it was in Physics that the great advance
was first made in the sixteenth century, once this new
Science had firmly won its place, Aristotle and his teach-
ings became very much discredited.

His answers to the two great questions of the time were
also very far from the truth, but because they were
Aristotle's answers they were implicitly believed until
finally disproved in modern times. As to the constitution
of matter, Aristotle taught, like Pythagoras, that there
were four elements earth, air, fire, and water. Each
element also was supposed to possess two out of four
primary qualities heat, cold, moisture, and dryness.

ARISTOTLE 25

Thus earth was cold and dry; water was cold and moist;
air was hot and moist ; and fire was hot and dry.

Aristotle's idea of the universe was that the earth was
fixed at the centre, and round it the moon, the sun, the
planets, and the fixed stars revolved on separate spheres.
So firmly did people believe that this view of the universe
was the correct one that it almost became part of their
religion, and hundreds of years later men who believed
that Aristotle was wrong were persecuted and imprisoned
for saying so, and one man was even burnt to death.

But there is one branch of science in which the work
of Aristotle can win nothing but praise, that is in Biology.
Before he became tutor to Alexander he spent two years
on an island in the Mediterranean, watching and studying
animal life, especially fish. The results of this careful
study he wrote down in books which have come down to
us, and later added observations made with the help of the
students of the Lyceum. The books about animals are
the only ones which have reached us, though probably he
also wrote about plants. Biologists of to-day are still
amazed at the wonderful accuracy with which Aristotle
described the life and habits of the creatures he watched.
He also studied, by dissection, the structure of their
bodies, and by examining eggs at various stages of incuba-
tion was able to trace the development of the chick inside
the egg.

In all Aristotle is said to have written between twenty
and thirty books on various subjects, although quite likely
much of what is said to have been written by him was
really written by others.

Now let us consider just what of good service Aristotle
did for Science, and what of bad. His greatest contribu-
tion was unquestionably that spirit of eager curiosity and

26 THE ROAD TO MODERN SCIENCE

of inquiry which he brought to bear on every subject he
investigated. That is the spirit which is to be found in
every great scientist. His great dis-service was in stating
so many things as facts, without first putting them to the
test of experiment. Unfortunately his followers, especi-
ally those mediaeval Christian monks who wove his
teaching in with the teachings of their Church, thus giving
them double authority, accepted blindly and unquestion-
ingly his writings and ignored, or perhaps never even
glimpsed, the man himself the eager, curious seeker
after truth. It was these men who were the true enemies
of science.

Aristotle, then, built a great new stretch of the road of
science. He made it wide and many travelled after him.
The goal was clear in front of him, but he did not choose
the right route, over the firm practical foundation of
experiment. Thus, although the way looked straight
and clear, the foundations of the road were faulty, and
men coming after him sank and were lost in the mire of
superstition and hearsay ; or struck aside in search of will-
o'-the-wisps that beckoned them astray.

CHAPTER V

Science in Alexandria

THE way now leaves Greece and again runs, for the next
five hundred years, through Egypt. But the road-makers
are still for the most part Greek by birth.

While Aristotle was teaching at the Lyceum in Athens,
Alexander the Great was busy carrying out his conquest of
the eastern peoples of Mesopotamia and Persia and of
Egypt. In the last named, on the delta of the Nile, he
founded the great city of Alexandria, which rapidly
became a most important centre of trade and commerce.
On the death of Alexander, his great empire was divided
amongst his generals, and Egypt fell to Ptolemy, who
was the wisest and ablest of them all. Under him
and, later, his son after him Alexandria continued to
flourish and became one of the most important cities of
the world.

Ptolemy, besides being a great general, was also a
learned man and liked to have always about him a group
of philosophers and men of science. The rest of the
empire, at that time, was in a very unsettled state, and so
philosophers from all parts were only too glad to come to
Alexandria and live peaceably under the patronage of
Ptolemy.

After the death of Ptolemy his son determined to erect
a building where all these philosophers could carry on
their work and teach the young men that came in a con-
tinual stream to learn from them. Accordingly, the great
Museum (or Home of the Muses) of Alexandria, was built,

27

28 THE ROAD TO MODERN SCIENCE

and for the next seven hundred years this was the great
centre of learning of all the civilised world.

The Museum was a very fine and beautiful building
standing amid lovely gardens in which were shrubberies,
flower-beds, fountains, statues, and alcoves. The build-
ing itself contained rooms of all sorts for study and
recreation, but the most important of all was its great
library. As many as possible of Aristotle's manuscripts
were stored here and as much of Greek literature as could
be procyred. It is said that one of the rulers of Alex-
andria made a law that any notable man visiting the city
must leave behind him a copy of any book he might have
in his possession. So in one way and another books were
collected until finally the great library is said to have
contained seven hundred thousand volumes.

Alexandria thus took the place of Athens as the centre
of learning and philosophy; and not only Greeks but,
later on, the Romans came to Alexandria to be educated,
just as, in the Middle Ages, from all over Europe young
men went to the universities of Italy and to Paris ; or, in
our country, to Oxford and Cambridge.

At first the teaching was much the same as it had be.en
at the Lyceum and the Academy, and Aristotle and Plato
were names greatly revered by all. Gradually, however,
a more practical side crept into the teaching. You will
remember that the Greeks of Athens despised practical
things and tried to make their teaching and thought as
abstract as possible.

In Alexandria, however, there was constant contact
with the natives of the country, the Egyptians and the
Arabs. These, as you know, were intensely practical
people, and undoubtedly influenced the Greeks living
amongst them. So, instead of studying pure mathematics

SCIENCE IN ALEXANDRIA 29

and geometry alone, without relation to any definite,
concrete matter, we find them studying mechanics that
is, mathematics applied to practical things such as the
invention of machines.

Of the many hundreds of learned men who studied at
Alexandria we can only mention three of the most out-
standing.

Euclid. Euclid was probably one of the first to come
over to Egypt and settle in Alexandria. We know very
little about the man himself, except that he lived some-
where about 300 B.C. and was possibly a pupil of Aristotle.
His great book of Geometry, however, is known to all,
though possibly not as bearing his name. Thirty or
forty years ago the study of this subject was invariably
known as 'Euclid'; and an English translation of the
original work the only text-book used in this country.
This book was really a collection of all the theorems in
Geometry already produced by many Greeks before his
time Thales, Pythagoras, and many others with some
original ones of his own. It was the first time that they
had all been collected together and arranged in order.
No other book of Geometry was used to any extent for
two thousand years.

Archimedes. Probably you already know a good deal
about Archimedes. He was born at Syracuse in Sicily
in 287 B.C. He went to Alexandria to study (possibly
under Euclid himself), and so, although most of his life
was spent in Sicily, he rightly belongs to the ' Wise Men
of Alexandria.' When he returned to Syracuse he
devoted the rest of his life to study, experiment, and
research. Notice that I said experiment. As a scientist
he was far superior to Aristotle, although his work was
far less well known until after the time of Galileo.

30 THE ROAD TO MODERN SCIENCE

Archimedes was really the founder of the science of
mechanics. He was an engineer and an inventor. He
it was who first discovered the 'Law of the Lever/ and
this he applied to the making of all sorts of practical
contrivances. The most famous story of his bringing his
ingenuity to bear upon a practical problem is, of course,
that about Hiero and his crown.

Hiero was the King of Sicily when Archimedes lived
there, and at one time he had a new crown made for him
out of a certain lump of gold, which he supplied to the
goldsmith. For some reason or other he suspected the
goldsmith of stealing some of the gold and substituting
silver in its place. The crown weighed the same as the
original lump of gold, of course ; and pure gold is not very
different in appearance from gold mixed with a little
silver ; so that the King could not tell from looking at the
crown whether his suspicions were right. He therefore
sent for Archimedes, who had made a reputation already
as being a very wise man, and asked him to try to find out
whether the goldsmith really had stolen any gold.

Now Archimedes knew that silver, bulk for bulk, was
lighter than gold ; so that if some silver were mixed with
the gold in the crown, the latter would be slightly more
bulky than if it were made from pure gold. What puzzled
Archimedes at first was how to find out just what was
the volume of the crown, because it was, of course, not
made in the shape of a nice regular cube, or other geo-
metrical body, which he could measure up. He was
probably thinking over this problem when, one day, he
went to the public baths. The vessel in which he took
his bath was quite full, so that when he got in some of the
water overflowed. Suddenly it dawned upon him that
just in proportion as his body was immersed so the water

SCIENCE IN ALEXANDRIA 31

overflowed; and if the water overflowing were collected
then he could measure the volume of his body in the
water. Here, then, was a way of finding the volume of
the crown. In great excitement he jumped from the
bath and rushed home without waiting to dress, crying,
'Heureka! HeurekaP 'I have found it! I have
found it ! '

He had next to find a lump of gold and a lump of silver,
each of the same weight as the crown, and to discover
the volume of each and of the crown by his new method.
The crown he found to have a volume larger than the gold
but smaller than the silver. So the goldsmith was guilty !

Yet, in spite of all the practical things he did, Archi-
medes' chief interest lay in abstruse mathematical
problems, having no bearing on the everyday needs of
life. He even went so far as to say that every kind of
art is ignoble if connected with these needs. He was,
indeed, a true Greek.

In 212 B.C. Syracuse was attacked by the Romans, and
Archimedes devised war- machines and other contrivances
with which to repel the besiegers. The enemy, how-
ever, entered and took the city. Archimedes was found
absorbed in one of his mathematical problems, of which
he had made a diagram on the sand. On the approach
of some Roman soldiers he called out to them not to
spoil his circle. This so angered one of the soldiers that
he promptly drew his sword and killed Archimedes, not
knowing who he was. The Roman general, however,
was angry at the news, for he had heard of his reputation
as a great man of learning. He caused Archimedes to
be buried with honour, and had a mathematical diagram
engraved on his tomb.

Ptolemy. After Archimedes, there is no great name

31 THE ROAD TO MODERN SCIENCE

worthy of mention for more than three hundred years,
until we come to Ptolemy, the great astronomer and
map-maker.

He was by birth an Egyptian, and studied at Alex-
andria. He is chiefly known because he wrote a very
important book called the Almagest, which means the
Great System; and this book was the standard work on
Astronomy for many centuries. In this book he col-
lected together the works of all the early Greeks and
added very many observations of his own. He then set
out to explain all these observations in the light of
Aristotle's teaching of the nature of the universe. This
was, you will remember, that the earth is a fixed and
immovable sphere at the centre of the universe and that
round it the other heavenly bodies travel in circles. The
reasons that Ptolemy gave in support of this theory
seemed very satisfactory at that time. The earth was
said to be a sphere because, during an eclipse, it cast a
circular shadow on the moon. This, of course, was
perfectly correct. Next, the earth was said to be im-
movable, because, were it moving, everything on it, but
not absolutely fixed to it, could not remain there, since
heavy bodies travel more quickly than lighter ones.
The lighter bodies on the earth would therefore get left
behind. This, of course, is a very sensible argument,
but unfortunately based on a wrong assumption about
moving bodies, as we have seen. Lastly, it was said that
the movements of the heavenly bodies must be perfect,
and therefore must be in circles ; for Plato had said that
these were the perfect curves. Unfortunately, Ptolemy's
observations showed him that the planets did not move
in simple circles round the earth. He, however, very
ingeniously invented a way in which he could make the

1*LATE 1

o

8

-o

SCIENCE tN ALEXANDRIA 33

planets move in circles and still occupy their observed
positions in the sky. He did this by supposing them to
move in epicycles! That means that each planet kept
moving in a circle round a definite point ; but the point
did not keep still but moved continuously in a circle
round the earth. The diagram, fig. 3, should make this
clear. Of course, it is not at all what the planets really

63)

FIG. 3. (a) the planet P moves in a circle round a point C
which moves in a circle round the earth, (b) Shows the
apparent path of the planet round the earth

do, but it saved Aristotle's reputation for quite a long
time.

Besides being an astronomer, Ptolemy was also a great
geographer. He wrote another book, which was used
for many hundreds of years, and which contained maps
of all the known parts of the world, including India,
China, and even Norway. These maps all contained
lines of latitude and longitude.

Apart from Archimedes, it cannot be claimed that the
Greeks of Alexandria did much to extend the already
existing road of Science. What they did was to keep
clear and make known the road of Aristotle and others
of the Golden Age of Athens. Archimedes, on the other

3

34 THE ROAD TO MODERN SCIENCE

hand, struck out for himself, a clear straight road by way
of experiment. He was a lone pioneer, however, and
his way became lost in the centuries that followed.
Nevertheless, it was his way that was followed by Galileo
when once again the effort was made to get back on to
the way with the firm foundation.

CHAPTER VI

Through the Dark Ages

So far we have only covered a comparatively short period
of about five hundred years since the time of Thales,
when Science, or the pursuit of knowledge for its own
sake, might really be said to have begun. The great
men we have talked about followed quickly, one after
the other, and there were very many more whom we have
not mentioned. Now we come to a long period of dark-
ness and silence in the history of Science when the path
gets almost lost in a wilderness of superstition and
quackery. This period lasts for about fifteen hundred
years, during which no one man stands out as worthy to
take his place beside the great * seekers after truth ' of the
Greek era. Yet, if we probe the darkness and the silence
of those long years we can follow the faint track whose
beginning was carved out so boldly in Athens and Alex-
andria, winding tortuously through the wilderness and
the gloom until at last it emerges suddenly into a
burst of light and brilliance in the sixteenth century
and becomes the great high road which leads directly
to our own twentieth - century world of scientific
wonders.

The conquest of Syracuse, in which Archimedes met
his death, was one of the early stages in the conquest
of the Greek empire by the Romans. Alexandria con-
tinued under the latter to be the centre of learning, but
the first brilliance which was attained under the Ptolemies
was never regained ; and except for the Egyptian Ptolemy,

35

36 THE ROAD TO MODERN SCIENCE

the astronomer and geographer in the second century,
no science of any moment flourished there.

The Romans themselves had no love for science. They
adopted the mathematics of the Greeks and applied it
very successfully to engineering and architecture, and the
fruits of this application are to be seen to-day in many
Roman remains, especially in some of their very wonderful
aqueducts for carrying water to their towns. But their
engineers and scientists were always servants and very
often slaves, and no honour was accorded to them. Small
wonder, therefore, that science did not thrive.

The Roman Republic merged into the dissolute and
decadent Roman Empire which, under Constantine the
Great, became nominally Christian. In the struggle
which had been waging between Christianity and Pagan-
ism the former now had the support of power and
authority, and a time of terrible destruction of all things
pagan began. It was at the command of one of the early
Christian Emperors that a great part of the Museum
Library at Alexandria was destroyed.

Even in Alexandria itself, though it was still nominally
a centre of Greek learning, the old spirit had entirely
disappeared. It was at this time that we find the first
beginnings of Black Magic and all its attendant evils and
superstitions which, in the centuries that followed, spread
everywhere throughout Europe and Arabia. What we
are chiefly concerned with here is the birth of Alchemy
or the art of making gold.

The Egyptians, you will remember, were well skilled
in metal work of all kinds. It was a common practice
with them to colour, by their arts, many of the so-called
baser metals so that they looked like gold. During the
third century A.D. there arose a cult of people known as

THROUGH THE DARK AGES 37

the Alchemists, who claimed, with the help of certain
Egyptian gods, to be able to turn these base metals into
real gold. The word 'Alchemy' means really the Black
Art. Whether this meant the hidden art because of its
secret nature, or whether it meant the art of the black
country because of the black mud surrounding the Nile
after flooding, is not clear. The cult was probably
originally limited to the Egyptian priesthood, but very
soon certain Greeks of Alexandria were admitted. It
was owing to these Greeks that Alchemy ever laid claim
to be called a Science.

At this time the writings of Plato were revered above
all others, and these early Greek alchemists sought and
found, as they thought, justification in them for the claim
that metals could be turned into gold. Plato, like
Aristotle, had taught that matter was of four kinds
earth, water, air, and fire but he had believed that it was
possible to turn one kind into another.

We really do not know very much about these early
alchemists, because we have very few of their writings ;
and those we have are so full of magic and superstition
and secret signs and symbols that it is almost impossible
to understand what they are about. One reason why
we have so few of their writings is that one of the Roman
Emperors became so frightened that a lot of gold might
really be made which would not belong to him that he
ordered all books which had anything to do with Alchemy
to be destroyed. In this way still more of the library at
Alexandria perished.

In the fourth century A.D. the Roman Empire was
divided into two an Eastern Empire with its centre at
Byzantium or Constantinople, and a Western Empire
still centred in Italy. Although the descent of the

38 THE ROAD TO MODERN SCIENCE

Teutonic barbarians on Italy destroyed the Western
Empire, the Eastern Empire continued to exist. As this
included Alexandria and Greece itself, the old manu-
scripts, or at any rate copies of them, were kept more or
less safely, chiefly in Byzantium. This city, however,
became entirely cut off from the rest of Europe until the
time of the crusades, and all trace of Greek culture dis-
appeared for the time in Western Europe.

Meanwhile, however, another channel was being pre-
pared through which these Greek writings should eventu-
ally reach Western Europe. We saw that Alexandria at
one time was the centre of learning for the whole of the
civilised world. Syrian and Hebrew scholars came there
also to partake of the Greek store of wisdom. As a
result of one of the many quarrels among the sections
of the early Christian Church, a great number of these
Syrians were expelled from the Eastern Empire where
they had settled and become Christian, and were forced
to return east to their own land. With them they took
copies of the precious Greek manuscripts which they set
about translating into their own language, Syriac. In
this way the culture of Alexandria was preserved in this
eastern land.

During the seventh century the foundations of the
Arabian Empire of Islam were laid by Mohammed ; and
within a hundred years of his death the Arabs had con-
quered the whole of Persia, Asia Minor, the North-East
of Africa, and were spreading into Spain. Although a
warlike race, the Arabs had a very great respect for the
learning of the Syrians whom they conquered. The
latter were given posts as physicians, astrologers, and
alchemists throughout the Empire. In the time of the
great Caliphs, great centres of learning and culture were

THROUGH THE DARK AGES 39

established, where the Syrian manuscripts were translated
into Arabic. Such centres were to be found at Basra,
at Baghdad of Arabian Nights' fame, and at Cordova in
Spain. Here, during the Middle Ages, came Europeans
to study, and so the old learning of the Greeks, now
interfused with later Arabic culture, returned once more
to Europe.

Arabian Science. It is probable that the Arabs added
little new to the knowledge of the Alexandrian alchemists,
but as our chief knowledge of the latter is from Arabian
writings it is not easy to be sure on the matter. The
pursuit of all the alchemists was, by this time, the search
for the 'Philosopher's Stone,' that substance which
should turn all metals into gold. In this search it was
inevitable that a fairly extensive knowledge of common
substances and their properties should have befen gained
and various methods of preparing them invented. All
the common chemical processes, such as distillation,
evaporation, crystallisation, etc., were known in those
days, though the vessels used were not like our modern
chemical apparatus of to-day. The only method of
heating was on an open fire, and a great many of their
vessels were made of fireclay and earthenware, although
glass was used to a certain extent. These vessels were
sealed or ' luted ' with clay, for corks and rubber tubing
were unknown.

The Arabs were amazingly clever workmen, and pro-
duced wonders in metal work of all sorts ; in dyed fabrics ;
and in glass and pottery ware. There are many storias
of the Moors in Spain, in which are to be found descrip-
tions of the magnificence and splendour amid which
they lived. Another very interesting thing we hear about
them is that they were the first to introduce the use of

40 THE ROAD TO MODERN SCIENCE

paper into Europe. This came to them from China by
way of Central Asia and Arabia. When paper was in use
the way was open for the invention of printing and the
use of books.

The Arabs studied the science of light and were
probably the first to make lenses a very useful art, as
Galileo found! They built observatories for studying
the stars and constructed many astronomical instruments
of types which are still in use to-day. In mathematics
they added little to the geometry beloved of the Greeks ;
but they produced the system of Arabic numericals (i, 2,
3, 4, etc., instead of the Roman I, II, III, IV), which we
use to-day. The invention of algebra is almost wholly
Arabic ; and the beginnings of trigonometry must also be
attributed to this people. In medicine they made great
advances.

While the Arabs were amassing and storing this
immense amount of detailed practical knowledge, Western
Europe was gradually settling down after the Dark Ages,
and kingdoms roughly corresponding to our modern
national divisions were growing up. The most im-
portant thing to notice is the growth of the power of the
Popes at the head of the now universal Church of Europe.
Most of these early Popes were very autocratic and very
jealous of any influence in men's lives other than that of
their own. Thus there came to be only one authority in
Europe, the authority of the Church ; and the word of the
Pope, through his priests, was obeyed unquestioningly.
The common man was allowed to have no intelligence or
mind of his own; and any attempt at freedom of thought,
either religious or otherwise, was stamped out with
cruelty and intolerance.

Next we must turn to notice the growth of the monas-

THROUGH THE DARK AGES 41

teries and of the mediaeval universities. Here the only
learning sanctioned by the Pope flourished, and here
gradually grew up that narrow and bigoted tradition with
which Galileo was to clash so violently. The first
monasteries were founded at the end of the fifth century,
and the monastic movement spread rapidly during the
seventh and eighth centuries. They were, of course, great
centres of light and learning during those very turbulent
times ; and the growth of education in Europe, and the
multiplication and storing of manuscripts, was due entirely
to them. At first the Church had little literature of its
own, and it was forced to depend on old Latin manu-
scripts of Roman writers. During the tenth and eleventh
centuries Arabic translations of the old Greek manu-
scripts found their way into Europe and were translated
into Latin the language of the Church. These had been
translated already into two different languages Syriac
and Arabian and as no translations are perfect, and mis-
takes in copying easily made, it is not to be wondered at
that these Latin translations were often very different
from the original. The manuscripts contained chiefly
the teachings of Plato, as interpreted by later writers, and
were mainly concerned with Alchemy.

In the twelfth century the Crusades brought about the
first contact between Eastern and Western Europe for
many a long year. Palestine was Beached by way of
Byzantium, where some of the more educated Crusaders
were attracted by the Greek manuscripts which they found
there. It was in this way that many of the writings of
Aristotle reached Europe and engaged the attention of a
learned monk named Thomas Aquinas. He translated
these manuscripts into Latin and made a very careful
study of them. He came to the conclusion that the

42 THE ROAD TO MODERN SCIENCE

teachings of that famous old Greek were fully in accord-
ance with the Roman Catholic doctrine. So Aristotle
received papal sanction. His writings were studied and
copied with such enthusiasm in all the monasteries and
universities that, within a comparatively short period, to
disagree with his teachings was heresy in the eyes of the
Church and punishable by fire.

During the centuries that followed, the works of Aris-
totle formed the central study at all the universities
throughout Europe, and that part of Aristotle's teachings
that these mediaeval professors and students learnt better
than anything else was to argue in a strictly logical
manner. To them, a learned argument came to be the
most convincing of all things far more convincing than
anything they saw or heard for themselves; and in the
great battle fought in the sixteenth century this was the
weapon which the opponents of the new science brought
with such confidence to the fray.

Alchemy. It is hardly surprising that, with the minds
of men turned so firmly towards the past, little advance
was made in science during those years. After all,
Aristotle had written an amazing amount about the
natural world, and that amply sufficed for these old
scholars. The chief science, so called, of that time was
the ancient art of Alchemy which came to Europe from
the Arabs. Attached to the court of almost every noble
was an alchemist, who, as a rule, practised also astrology
and magic. He advised his lord as to auspicious occasions
on which to carry out his activities. The idea of having
untold wealth at his command naturally inflamed the
imagination of each nobleman. Many a fraudulent experi-
ment was staged to convince him that the secret had been
gained and so assure continued favour for the alchemist.

THROUGH THE DARK AGES 43

Nevertheless, the majority of the really intelligent men
of the day honestly believed that transmutation into gold
was a real possibility if only the philosopher's stone could
be made. Their justification for the belief was to be
found in the views which they held concerning the nature
of matter, which views they derived from Aristotle. Let
us remind ourselves what they were :

Anything which occupied space consisted of matter
of some sort.

There were four different kinds of matter, called the
elements ; these were earth, water, air, and fire.

Solids consisted chiefly of the element earth, but
often contained smaller amounts of the other elements
which could generally be driven off by heat.

Liquids consisted chiefly of the element water.

By sufficiently altering the properties of a substance
as, for example, its appearance and texture it was
possible to turn it into something else. This is what
Aristotle taught.

In addition, the alchemists of the Middle Ages held
certain ideas as to how the metals came to be formed.
These had come down to them from the Arabs. From
the four elements present in the earth, the first compound
substances to be formed were mercury and sulphur.
These two mixed together beneath the surface of the earth
and under the influence of great heat and during the lapse
of a considerable period of time formed the metals. If
the conditions were quite perfect and the heavenly bodies
in favourable positions with reference to one another,
then gold, the perfect metal, was formed. If not quite
enough time was taken over the process, then not gold
but silver was the product; while if any, or all, of the

44 THE ROAD TO MODERN SCIENCE

other conditions were wrong, then either copper, tin, iron,
or lead were formed instead.

According to these ideas, therefore, the base metals
were thought to be just impure gold, or gold gone wrong
in the making ; and so it should not be so difficult to alter
those qualities which were wrong, such as colour, hard-
ness, etc., and get gold in the end. Needless to say, the
mediaeval alchemists were no more successful than their
predecessors ; but all the time they were improving their
methods of working; and from time to time new sub-
stances were discovered. Many of these are the coinrpon
reagents of our chemical laboratories to-day, although
they were then called by quite other names. For instance,
what we call nitric acid they called aqua fortis (strong
water), because it would dissolve so many metals ; while
aqua regia, which is a mixture of nitric and hydrochloric
acids, was so called because it alone would dissolve that
king of metals, gold. They also discovered what they
called spirits of salts (hydrochloric acid), spirits of harts-
horn (ammonia), and many others. Nevertheless, in
spite of such discoveries, no real advance was made in
understanding the nature of the materials they used and
the reason for their various reactions upon each other. It
was not until the seventeenth century that chemistry as an
ordered science came into being.

Paracelsus (1493-1541). Before that, however, the
search for new substances was widened considerably
owing to a man commonly known as Paracelsus (his real
name was Theophrastus Bombastus von Hohenheim!).
He was a Swiss physician who lived in the sixteenth cen-
tury very much later than the times we have been talking
about, but still before the birth of modern chemistry. He
taught that a great deal of talent and energy was being

THROUGH THE DARK AGES 45

wasted in this search for the philosopher's stone. These,
he said, should be turned instead to the study of sub-
stances with a view to their use as medicines, and especi-
ally should search be made for that substance, the Elixir
of Life, which should prolong life indefinitely.

Paracelsus fell out very badly with the rest of his
profession because he publicly burnt all his books written
by Galen and Avicenna, the two great authorities on
medicine ; and said that, henceforth, he would rely only
on his own powers of observation and his experience
gained by the use of his medicines.

He had some very curious ideas as to how our bodies
function, but these do not concern us here. He also
produced a new theory as to the composition of matter,
substituting for Aristotle's four elements the three
'principles' of sulphur, mercury, and salt. The part of
a substance which would burn contained the principle
of sulphur; that which would volatilise or turn into
vapour when heated contained the principle of mercury ;
while the solid which remained when all the sulphur and
mercury had been driven off contained the salt.

By this time, you see, the yoke of Aristotle had been
lifted somewhat and new ideas were being produced. It
cannot be said, however, that the new theory of Paracel-
sus was a great improvement. What is to his credit,
however, is the impetus which he gave to the search for
new chemical substances.

This, then, is the story of Alchemy up to the middle of
the seventeenth century, and to make it complete we
have really gone too far ahead in time. Now we must go
back again to the thirteenth century and hear about one
man who realised what shackles bound men to the past
and had a vision of what true science ought to be.

46 THE ROAD TO MODERN SCIENCE

Roger Bacon (1214-1294). This man was Roger Bacon,
an Englishman. Because of his new way of looking at
things he has been called 'the Herald of the Dawn.'
Like all the educated men of that time, he was a monk ;
but he was a very unorthodox monk and frequently in
hot water because of his outspokenness. He claimed that
the true way to acquire knowledge was by experiment and
not by argument ; and that authority (for example, what
Aristotle said) carried no weight if experiment said other-
wise. He lived up to his teaching by carrying out a great
many experiments; and he made a number of new and
valuable discoveries, more especially in connection with
Light. He was an alchemist as well, and believed in the
possibility of transmutation. He wrote down the results
of his experiments, together with his ideas on how science
should be studied, in three books which he called Opus
Mains and Opus Minus and Opus Tertium. As you
might expect, these books were not at all popular with the
authorities, and he was put into prison for writing them.
He was kept there for fourteen years, and was only re-
leased, to die almost at once, in his eightieth year.

Leonardo da Vinci (1452-1519). After Roger Bacon
came another period of three hundred years when no
name stands out as worthy of mention, except that of
Leonardo da Vinci. This great Italian lived about two
hundred years after Roger Bacon, and a hundred years
before Galileo. Leonardo da Vinci is, perhaps, best
known as a painter; he painted the famous picture of
the ' Last Supper ' and also the portrait known as * Mona
Lisa,' both of which are considered to be amongst the
world's greatest pictures. Only comparatively recently
has it been realised that his genius was by no means
limited to painting or any form of art. He had a passion

THROUGH THE DARK AGES 47

for knowing the truth about things, and his notebooks are
full of drawings and notes on every conceivable subject,
from designs for flying-machines to the habits of poisonous
spiders. He loved mathematics, and by its aid designed
a great variety ofrmachines, many of which were used by
his patron, the Duke of Milan. He scorned the al-
chemists in their search after gold, and fully realised the
impossibility of transmutation. His notebooks show that
he discovered many things which did not become gener-
ally known until their rediscovery by others much later.
One writer about Leonardo has said that if Galileo is
called the ' Father of Experimental Science/ then
Leonardo da Vinci might be called its grandfather !

Certainly both Roger Bacon and Leonardo da Vinci
broke away from the darkness and reached the light but
the rest of their fellows were not ready to follow them.
So no permanent way was yet made.

CHAPTER VII

The Dawn of a New Age

THE man who actually ushered in the new age of science
was Nicholas Copernicus. He was born in 1473 at Thorn,
in Poland, on the River Vistula. His great contribution to
Science was his conclusion, arrived at after a lifetime of
careful observation of the heavens, that it was the earth
which moved round the sun and not the sun round the
earth, as all the world then believed because of the teach-
ings of Aristotle and Ptolemy.

Copernicus first went to the University of Cracow with
the object of becoming a doctor. He soon found, how-
ever, that he was far more interested in mathematics and
astronomy than in medicine. After qualifying to be a
doctor he devoted himself to the study of these two other
subjects, and before very long he became Professor of
Mathematics at Rome. He did not stay long at Rome,
however, but, being appointed a canon in the cathedral
of Frauenburg, he returned to his own country. Here
it was that he spent the rest of his life and carried out
that wonderfully exact series of observations which
finally led him to his famous decision as to the true state
of affairs among the heavenly bodies.

Let us see how he carried out these observations.
Remember that the telescope was not yet invented, nor
many of the other great instruments of our modern
observatories. First we must understand just what it
was that he had to do. Imagine a great circle passing
through the North and South Poles and the point

4 8

PLATE II

An Alchemist at Work

PLATE III

O

*2

o
U

o

O

"H

rt

O

THE DAWN OF A NEW AGE

49

immediately overhead (the zenith). This circle is called
the meridian. The sun crosses the plane of this circle
every day at noon, and at some time during the twenty-
four hours every star crosses it. The time at which each
star does this is a very important determination in
astronomy. To carry out these determinations, he

FIG. 4. The meridian. The shaded area indicates the plane of
the meridian, at right angles to the plane of the paper

arranged slits in the walls of his house so that he could
note the 'transit' of the stars across the meridian. He
also made himself an instrument called a quadrant, by
which he could measure the altitude of each star as it
passed.

Copernicus studied especially the movements of the
planets, and it was this study which led him to his famous
conclusion. Now it is most important that you should
not think that it was quite a new idea to Copernicus that
the earth should move and the sun stay still. He was a
very well-educated man and definitely tried to read as

4

50 THE ROAD TO MODERN SCIENCE

many as he could of the writings of the ancient Greeks
about their ideas of the universe. Thus he knew very
well that although Aristotle had taught that the earth
was still, Pythagoras had said that it, and the planets,
moved round a central fire; while a later astronomer,
Aristarchus, had actually taught that the sun was the
centre round which the earth and the planets moved.

, s a measure,
I of the afhtudk, oftfit,Sfar

U

FIG. 5. A simple quadrant

What Copernicus did, therefore, was to show that the
motions of the planets, as he had observed them, were in
agreement with the theory of Aristarchus rather than
with that of Aristotle and Ptolemy.

Copernicus was a very modest and retiring man and
was not at all anxious to make his views known, but his
friends finally persuaded him to publish them. This
he did in the famous book called De Revolutionibus Orbium
Caelestium. This, however, was not until he was an old
man, and before it was published he was smitten with a
paralytic stroke, and it was only a few hours before his

THE DAWN OF A NEW AGE 51

death in 1543 that the first copy of the book was put into
his hands.

Now, although Copernicus was a canon of the Church
he realised that his book would be extremely unpopular.
Nevertheless he dedicated the book to the Pope, and
expressed his conviction that the ideas which it contained
were not contrary to the truest and best teachings of his
Church.

At first the Pope was immensely pleased by the dedica-
tion ; but when once the contents of the book were fully
understood, it called forth quantities of abuse, and any
man proclaiming himself to be a convert to the Copernican
view suffered great disrepute. Indeed, a certain man
named Giordano Bruno was imprisoned for six years and
finally burnt at the stake.

Before we come to Galileo, who was the greatest of all
the supporters of this theory, there are two men whose
joint work was tremendously important to the progress
of the new astronomy. The first of these, Tycho Brahe,
was never a convert to the Copernican theory, while the
second, Kepler, was its keen supporter from the first.

Tycho Brake. Tycho Brahe was a Dane of very good
birth. At that time it was not at all usual for well-born
people to receive a good education, but luckily Tycho
Brahe had an uncle who was himself well educated, and
he adopted this nephew and sent him to the University
at Copenhagen. He was really meant to study law, but
the occurrence of an eclipse which had been predicted
so fired his interest in astronomy that he decided to devote
his life to its study.

From the first, his real interest lay in making observa-
tions of the heavenly bodies rather than in inventing
theories to account for their movements. This was just

52 THE ROAD TO MODERN SCIENCE

as well, as the one theory he did put forward was not at
all a brilliant one. On the whole, he was a fairly steady
supporter of Ptolemy's system all his life.

Tycho Brahe was at once struck with the inaccuracy
of all the observations of the stars which had been made
hitherto, even those of Copernicus. He therefore set
about making much larger and more elaborate instru-
ments, and by their aid was able to carry out observations
far exceeding in accuracy any which had previously been
made. This accuracy was due not only to the superiority
of his instruments but also to the skill and care of Tycho
Brahe himself.

The King of Denmark was greatly impressed by his
ability, and seemed to have realised that every help and
encouragement should be given to a man of his eminence.
He therefore gave him an island and 20,000 with which
to build an observatory. This observatory, which was
called Uranienburg (the castle of the heavens), was a
wonderful affair when it was built. It was fitted with
laboratories and workshops, and in the actual observa-
tories with the most splendid instruments that Tycho
Brahe had so far made. Here for the next twenty years
he gradually accumulated the most complete and accurate
set of observations on the heavenly bodies that had ever
existed. He won great renown as a man of Science, and
was visited by eminent personages from all over Europe.

Unfortunately, when his patron the King of Denmark
died, he lost favour with the new king and had to abandon
his wonderful castle. After two years of wandering in
Europe he was invited by the Emperor of Bohemia,
Rudolph II, to settle in Prague, and was given a castle,
to which he was able to bring his instruments. Once
more students flocked to him, and an important piece

THE DAWN OF A NEW AGE 53

of work was begun which he called the Rudolphine Tables
astronomical tables intended for the use of navigators.
But the anxiety and privations of the last years had so
told on Tycho Brahe that he soon fell ill and died in
1 60 1, committing to Kepler, on his death-bed, the work
of completing the Rudolphine Tables.

Kepler. Johann Kepler was born in very different
circumstances from Tycho Brahe. His mother was low-
born and bad tempered, and his father continually in
money troubles. When four years old Kepler suffered
from smallpox, which left him with impaired eyesight
and an unsteady hand. At ten years old he was taken
from school and served as a pot-boy in a tavern which
his father was keeping at the time. Later, however, he
was able to attend a monastic school and finally managed
to get to the University of Tubingen. Here the pro-
fessor of mathematics soon detected Kepler's genius and
at once introduced him to the doctrine of Copernicus to
which he himself was an acknowledged convert. Kepler
became a powerful defender of this doctrine and soon
established a considerable reputation. At twenty-three
years of age he was offered a professorship in Astronomy
at the University of Graz, which he accepted for the time
being, but determined to look out for something better,
as the salary was not at all good and he was tired of con-
tinual poverty.

The question which most of all interested Kepler was
whether there was a definite scheme governing the move-
ment of the planets. There were still only six planets
known Mercury, Venus, the Earth, Mars, Jupiter, and
Saturn ; and of course it was only people who believed
in the Copernican theory who thought of the Earth as
a planet, Kepler also knew that Saturn was the farthest

54 THE ROAD TO MODERN SCIENCE

from the sun and moved most slowly, and that Mercury
was nearest and moved the fastest. What he wanted to
find out was why there were six planets no more and
no less; what was the connection between the orbit or
path in which they travelled round the sun, the time they
took to travel round it and their distance from the sun ?
It was to the answering of these questions that he devoted
his whole life, and success crowned his efforts finally in
a very brilliant fashion.

While he was at Graz he evolved his first theory con-
cerning the planets. This was very elaborate, rather
fantastical, and proved to be wrong, but I mention it here
because it was probably this theory which brought him
into touch with Tycho Brahe. The latter had by this
time been compelled to leave Uranienburg and was then
at Prague. Kepler wrote to ask if he might visit him in
order to find out whether Tycho's observations on the
planets would support his own theory about them. Tycho
at once told him to come and share his work with him.
Now Kepler, owing to his weak sight and general ill-
health, was quite unfitted for such work, which meant
much outdoor work at night, good eyesight, and a steady
hand. He was therefore rather reluctant to accept the
offer, but finally did so, and was before long appointed
by the Emperor as Tycho's mathematical assistant. He
quickly found that his first theory must be abandoned
as it did not fit the facts, and set to work again on the
problem. In the meantime, however, Tycho Brahe died
and entrusted to Kepler the completion of his Rudolphine
Tables. The Emperor had been involved in wars and
other political complications, and Kepler found it almost
impossible to get the money to go on with the work.
Eventually, however, after long delay, they were com-

THE DAWN OF A NEW AGE 55

pleted, but money was still required to publish them.
For four years he tried to get the money from the Emperor,
but at last he was compelled to raise the money for it
himself. All his life he was desperately poor, as he never
could get his salary paid. Where he got the money from
to publish the tables is not known, but somehow or other
he managed to keep his promise to his friend and bene-
factor. The publication of these tables was a very import-
ant event in the history of astronomy, as they were the
first really accurate tables which navigators ever possessed.
All this time he had been going on with his own work,
and success had at last crowned his efforts, atoning in great
measure for the misery and privation he had to endure.
You will remember that he was trying to find out about
the connection between the orbits in which the planets
travelled and the time in which they described those
orbits. At first he, like everyone else, assumed that
they must travel in circles round the sun at the centre.
This was, I suppose, really because Plato and Aristotle
had both said that the circle, being the perfect curve,
must be the path in which the heavenly bodies moved.
Ptolemy, it will be remembered, found that his observa-
tions of the planets showed that they did not travel in
simple circles round the earth; and so he invented epi-
cycles. Kepler tried all sorts of ideas, but had no success
until he gave up trying to use circles at all. It is only
possible here to state, quite simply, what he eventually
discovered. His methods were entirely mathematical
and we cannot follow him into that region. This is what
he found out :

(i) Each planet moves in an ellipse round the sun,
which is at one focus. (Look at the diagram to see
what the focus is.) \^7 f^^Q

5 6 THE ROAD TO MODERN SCIENCE

(2) If a straight line were drawn between the sun
and the planet, then that line would sweep over equal
areas in equal times. (Again look at the diagram.)

(3) He also found out that there was a definite
mathematical connection between the time taken by
any planet to revolve round the sun, and its average
distance from the sun.

FIG. 6. FX and F 2 are the foci of the ellipse. The sun
is at the focus F 2 . The planet moves from P l to P 2 ,
Pa to P 4 , and P 6 to P e in the same time if the shaded
areas are equal

The beauty about Kepler's discoveries is that there was
no doubt about their being true. They were found
entirely from Tycho Brahe's observations. So you see
the two men were absolutely necessary to each other.
Kepler could not possibly have discovered his laws with-
out Tycho Brahe's observations, and these observations
would have been of far less value if they had not been so
brilliantly interpreted by Kepler. Kepler published his
results in a book in which he set forth plainly the
Copernican theory. It was at once suppressed and placed

THE DAWN OF A NEW AGE 57

on the list of books prohibited by the Pope side by side
with the work of Copernicus himself. His work at the
time was very little appreciated, and when he died in
1630 it was as a result of exhaustion after a fruitless
journey to Prague to try to get some of the money due to
him from the Emperor. Everything was against him all
through his life, and yet his achievements were great. He
produced the beginnings of law and order out of chaos
and paved the way for the genius of Newton.

CHAPTER VIII

Galileo

THE real hero, and the leader, of the great revolution in
Science was Galileo Galilei, who was born in Florence,
in Italy, in 1564. He it was who once and for all turned
away from the old road of Aristotle and set his face
towards the firm ground of practical experiment.

When he was quite a boy he loved to make things with
his hands and to draw and paint. He believed in finding
things out for himself, and used to argue with his teacher
as to whether Plato and Aristotle were really right in what
they said and whether they had tried things for them-
selves.

When eighteen years old he made his first discovery.
He was in the cathedral of Pisa at his prayers one afternoon
when a choir boy went his round to light the lamps. From
the great dome of the building there was suspended on a
great chain a very beautiful lamp. The boy pulled this
lamp towards him, to light it, and then let it swing back.
Galileo stayed watching the lamp swing, casting its weird
shadows through the great building. Gradually the swing
died down and the lamp moved more and more slowly.
As he watched, it seemed to Galileo that although the dis-
tance over which the lamp moved was so much shorter yet
it took just about the same time to cover it as did the first
longest swing of all. But a rough guess was not enough
for Galileo. He had no watch, but instead he put his
fingers to his pulse and counted. He was right; every
swing even the last little one before the lamp was still

58

GALILEO 59

took just the same time. Experiments of his own showed
him that the length of time a pendulum takes to swing
depends, not on the distance through which it swings,
but only on the length of the chain or string. The
longer the string, the slower is the rate of swing. Galileo
then made a little instrument, consisting of a weight on a
thread, for doctors to use to measure a sick person's
pulse. The thread could be adjusted so that the pen-
dulum swung in time with the pulse. A long string
would mean a slow pulse and a short string a quick one.
Later, of course, Galileo's discovery was made use of in
making clocks, such as grandfather clocks and many of
the big clocks on buildings.

Galileo's father badly wanted him to be a doctor, but
Galileo had set his heart on learning mathematics. Now
at that time it was a much more paying proposition to be
a doctor than to teach mathematics, and his father warned
Galileo that if he persisted he would be very poor. He,
however, cared nothing for that, and at twenty-six years
of age he was made Professor of Mathematics at Pisa.

From the very first he was a nuisance to the other pro-
fessors, because he would argue about things instead of
quietly accepting what Aristotle or Plato had had to say
on the matter. I have already described how he got them
all together outside the leaning tower of Pisa, and, climbing
the tower, dropped his two weights, one heavy one light,
so that all could see them reach the ground together, thus
proving Aristotle wrong. This incident made him very
much disliked, and from then on he made many enemies,
who were to do him much harm in later years.

He soon had to leave Pisa, and from there he went to the
University of Padua as Professor of Mathematics, where
he remained for the next eighteen years, teaching and also

6o THE ROAD TO MODERN SCIENCE

experimenting on his own. At this time the new theory
of Copernicus was being very greatly discussed, and in
1600 Bruno was burnt to death at Rome. It is not sur-
prising to hear that Galileo was a firm believer in this new
theory, and in fact became its chief defender.

In 1609, Galileo heard of a wonderful instrument made
by a Dutch spectacle- maker. This consisted of two lenses
so put together that when distant objects were viewed
through them they appeared much larger and nearer than
when viewed with the naked eye. When Galileo heard
about this he realised what a valuable possession such a
contrivance would be. He at once set to work to try to
make one. He did not then know very much about
lenses, but his ingenuity finally triumphed and he
succeeded in making his first telescope. One can
imagine with what excitement he began to use his new
possession, and it was not long before he turned it away
from the earth to the heavenly bodies. At once new
worlds were opened to him. He found that there were
mountains on the moon, spots on the sun, rings round the
planet Saturn, and no fewer than four moons or satellites
revolving round Jupiter.

These discoveries also caused much excitement amongst
other people. Here is a description of its effect on the
people of Venice, which Galileo wrote himself. 'As the
news had reached Venice that I had made such an instru-
ment, six days ago I was summoned before their High-
nesses, the Signoria, and exhibited it to them, to the
astonishment of the whole senate. Many of the nobles
and senators, although of a great age, mounted more than
once to the top of the highest church tower in Venice, in
order to see sails and shipping that were so far off that it
was two hours before they were seen, without my spy-

GALILEO 61

glass, steering full sail into the harbour; for the effect
of my instrument is such that it makes an object fifty
miles off appear as large as if it were only five ! '

Galileo gave a spyglass possibly the original one
to the Doge, or Grand-Duke, of Venice. There is still at
Florence one of the telescopes which Galileo made,
though whether it is this one I do not know. (See Plate V.)

His discoveries about the heavenly bodies, however,
were not at all favourably received by the followers of
Aristotle, who produced all sorts of learned arguments
and quotations to show that Galileo was wrong. Most
of them refused utterly to look through the telescope. I
will quote just one bit of their reply to Galileo about the
moons which he claimed to have seen revolving round
Jupiter. * These satellites of Jupiter are invisible to the
naked eye, and therefore can exercise no influence on
the earth, and therefore would be useless, and therefore
do not exist.' To us this may not seem at all a sensible
argument, but we live a great deal further along the road.

There is not time here to make it clear to you how all
these discoveries of Galileo lent a great deal of support to
the Copernican view of the universe, as opposed to that
of Aristotle. You will, however, see at once that, with a
telescope as an aid to vision, it was possible to find out
a great deal more about what was going on in the heavens
than it had been before. Galileo did not of course make
all his discoveries at once with the first telescope. For
the next few years he was hard at work continually im-
proving on this first instrument. He taught many
students how to make telescopes, and continually had
them at work preparing new and better ones. In this
way the use of the telescope gradually spread through
Europe, and we find many more men at work studying

62 THE ROAD TO MODERN SCIENCE

the heavens. Gradually with his improved instruments
Galileo found out more and more, and was absolutely
convinced that the old monk, Copernicus, had been right
in his theory.

He was not at Padua all this time. Although the
senators of Venice, who had appointed him to the pro-
fessorship, were very pleased with him after his invention,
and gave him a much bigger salary, quite soon afterwards
he left Padua and went to live at Florence as Mathe-
matician and Philosopher to the Grand Duke of Tuscany.
This gave him much more time for his own work in
astronomy, as now there were no daily lectures to be given.
There was also, however, a less fortunate side to this
move. Unlike Venice, which was a free republic, Tus-
cany was very much under the influence of Rome and the
Pope. His old enemies, the Aristotelian professors, got
to work and tried to stir up Rome against him, because of
all the heretical views he was teaching about the heavens.
Soon he was sent for to Rome and asked to explain his
views to the Pope and the College of Cardinals. He was
very nearly as good at argument as the professors them-
selves, but he had not the weight of authority behind him.
At first the Pope was impressed and inclined to be well
disposed towards him, but in the end his enemies won.
Galileo was told that if he did not cease to teach his * false,
impious, and heretical opinions ' he would be imprisoned
and tortured. Reluctantly he gave his promise and was
allowed to return to Florence.

For the next seven or eight years, Galileo was very care-
ful of what he said, although he went on all the time with
his researches. Then the Pope died, and Galileo managed
to get into the good graces of the new Pope. This led him
to think that perhaps now he could venture to put forward

GALILEO 63

his true opinions once more. He therefore began to
write a book in which he set forth very clearly the Coper-
nican system and the evidence in favour of it. He was
very tactful in the way in which he did this. To begin
with, he wrote it in the form of conversations between two
men, one of whom upheld Aristotle's theory and the other
that of Copernicus. Now this was a method of writing
a book often followed by the ancient Greeks especially
by Plato. Secondly, he tried to be very fair to Aristotle
in the conversations, although of course the latter was
made very obviously to get the worst of the argument.
When the book was published, it was read eagerly by
everyone ; but Galileo's enemies were roused at once and
easily turned the Pope against him as well. The book
was banned and Galileo ordered to come to Rome at
once. It was now more than twenty years since he had
invented the telescope, and he was becoming an old man.
At Rome he was subjected to the famous Inquisition.
He held out for a while, but finally, old and broken, he
gave in and recanted, declaring that he acknowledged his
new doctrine to be in opposition to the teachings of the
Holy Scriptures, and swearing never more to teach it in
any form whatsoever.

Copies of this recantation of Galileo's were sent to all
towns throughout Europe and read publicly from every
pulpit. The anxiety of the trial and the final disgrace
had so affected the health of his favourite daughter that
soon afterwards she died, and Galileo was thus left with
this added grief and loneliness to bear. He was not kept
a close prisoner for more than a few days, but was only
allowed to return to his home outside Florence on con-
dition that he remained there and never went outside it.
Here he spent the remainder of his days, but not in

64 THE ROAD TO MODERN SCIENCE

idleness. He now turned his attention to a subject which
had greatly interested him before the invention of his
telescope led him to the study of astronomy. This was
an investigation of the laws which govern bodies in motion.
Again I am not going into details as to what he really dis-
covered here. It was very important and very valuable
and laid the foundation of the work which was to be com-
pleted by his brilliant successor Isaac Newton. I shall
say more about it when I come to him.

During these years a further misfortune befell him, for
he became blind. He had, however, with him one or two
devoted pupils who acted as secretaries to him and wrote
his notes. One of them was Torricelli, the inventor of
the barometer.

After a while, Galileo was not kept so closely secluded,
and people were allowed to visit him. From all parts of
Europe eminent people visited this now famous old man,
amongst them the poet Milton, from our country.
Galileo was failing in health, however, and in 1642 he
died, at the age of seventy-eight years. Although
honoured by many, he was still in disgrace with the
authorities, who permitted no public funeral nor allowed
a monument to be erected over his grave. They were, of
course, powerless to stop the spread of the new doctrine,
and by their very persecution roused the interest of all the
educated people in Europe, so that Galileo soon earned
the fame he deserved.

Now how was it that Galileo succeeded where Roger
Bacon and da Vinci failed ; that is, in definitely opening
up the new and straight road of real scientific progress ?
It was probably more to do with the times in which they
lived than in the men themselves, although Leonardo
certainly had not the fighting personality of Galileo.

PLATE IV

^ii^^^^^s '*"" s *! 7 ^lt* 11^*1" '' I

SFTtlte^i* jfTMlTfvr} | 11 " i

' w < tt ** r Vj Jb * i

,it*wte*i !

JNIW *! *.T*M ft*S*;Cr" j

I

Tycho Brahe in his Observatory

Note the use of the quadrant and the slit (top left-hand
corner) to measure the altitude of a star. This gave a much
more accurate measurement than any previously obtained by
similar methods

GALILEO 65

Bacon, however, appears to have been of much the same
calibre, and was as firm a believer in the value of experi-
ment as Galileo. He, however, lived before the time of
the Renaissance and of the Protestant Reformation. Men
were not ready to break away from the old authority into
new paths, and he therefore travelled a lonely journey
and none sought to follow him. In Galileo's time, how-
ever, everywhere the Renaissance had done its work.
Men were ready for new ideas and only the Church clung
firmly to the old ways of thought. In many parts of
Europe the Church had lost its hold and Protestantism
and freedom of thought reigned instead. It was only
because Galileo lived so close to Rome and in a state still
within the jurisdiction of the Pope that he suffered so
much from persecution. Thus, while he still lived, he
was already gaining converts to the new view of Science,
and at his death there were a number of real scientists in
various parts of Europe already engaged in carrying on
the road. As we shall see, the making of the road was
soon not to be the work of any one man alone, but of an
ever-increasing army.

CHAPTER IX

Newton, the Master Builder

FINALLY we come to the greatest of all the road-builders,
Isaac Newton. He strengthened, broadened, and made
clear the path already made by Copernicus, Galileo, and
Kepler, and, in addition, laid a broad, new stretch of his
own. Thus the narrow road, hitherto trod by only a
few of the boldest and most far-seeing, was now trans-
formed into a great thoroughfare, along which all who
took the trouble to learn the rules of the road might
follow. After Newton came a whole army of workers
who now divided the road into separate ' tracks/ running
side by side. The workers on each of these occupied
themselves with just one branch of Science. For
scientific knowledge had grown so great that it became
necessary to divide it into various branches. These were
Astronomy, Mathematics, Physics, Medicine, Chemistry;
and later, Biology, Geology, and Physiology. There are
many great names connected with all these great branches
of Science, but almost all of them owe something to
Newton, who set forth so clearly the ' rules of the road '
and invented new and useful tools with which to work.

In the year that Galileo died, 1642, Isaac Newton was
born in a small village in Lincolnshire. His father, who
died before he was born, owned a small manor, which
his son, therefore, inherited from him. At the local
school at Grantham, Isaac at first by no means distin-
guished himself, being far more interested in making
toy models and mechanical contrivances than in the

66

NEWTON, THE MASTER BUILDER 67

study of books. However, this state of affairs was altered
in rather an amusing fashion. One day he had a fight
with a boy, bigger and older than himself ; and succeeded
in thrashing him. His self-esteem thereby rose exceed-
ingly, and, spurred to further efforts, he turned his
attention to his school work, with such success that he
was soon top of the school.

When he was fifteen his mother felt it was time to
train him to manage his own land, and he therefore left
school. He soon found, however, that he had no liking
for farm work, and invented many ways of dodging it.
Whenever possible he retired to an attic, or to a secluded
seat beneath a hedge, and devoted himself to his books
or to the invention of some new contrivance. His
mother, despairing of her son as a farmer, sent for her
brother to advise her. Isaac was found sitting under a
hedge with a book on mathematics, when he should have
been attending to his work on the farm. His uncle
wisely advised letting him give up the idea of farming and
go to Cambridge.

A new and marvellous world now opened out for
Newton. His education at the local school had con-
sisted entirely of Classics; of mathematics and science
he knew nothing except the little he had picked up on
his own. He read everything he could lay hands on
and soon made good his past deficiencies. After taking
his degree he helped the Professor of Mathematics at
Cambridge with some work on Light, or Optics, as it
was then called. It was in this subject, together with
Mathematics and Astronomy, that his greatest work was
done.

In 1667 Newton was made a Fellow of his college
(Trinity College), and two years later succeeded to the

68 THE ROAD TO MODERN SCIENCE

professorship of mathematics, which he held for the next
twenty-five years. Nearly all the men about whom we
have been talking have been unsuccessful and unpopular
during their own lifetime. This was not so with Newton.
From the first his genius was recognised at Cambridge,
and shortly after being made a professor there he was
elected a Fellow of the Royal Society. This is the oldest
and most famous of all scientific societies, and had been
started during the time of Cromwell's rule in England.
Charles II was greatly interested in the Society and
granted it a Royal Charter in 1662. Charles was still
reigning when Newton was elected a member.

When William of Orange became King of England
he found the money affairs of the country in a very bad
state, and the coinage in a much debased condition. An
effort was made to improve this state of affairs, and
Newton was offered the position of Warden of the Mint.
As he was able at the same time to continue in his
professorship, he accepted the offer, and carried out the
work so successfully that he was promoted to be Master
of the Mint three years later, with a considerably in-
creased salary. In addition, in 1699, he was enrolled by
France as the first foreign Associate of the Academic des
Sciences. So you see that even during his own lifetime
Newton was honoured and appreciated by all sorts of
men; and yet apparently he was of a very modest and
retiring nature, and often had to be persuaded by his
friends to publish his important discoveries.

Now let us see what these discoveries were. I have
already said that he devoted himself mainly to mathe-
matics, optics, and astronomy. His discoveries in mathe-
matics are beyond the ken of most of us; although 'the
calculus' is becoming far more widely taught than

NEWTON, THE MASTER BUILDER 69

formerly. This was a mathematical invention of Newton's
which has proved to be extraordinarily useful to
modern scientists and engineers. That is one of the
'tools' which Newton made, of which I spoke earlier
in this chapter.

His work in optics you will be able to follow more
easily. For instance, you are probably quite familiar
with the rainbow colours which are seen when light falls
on the bevelled edge of a mirror or passes through a

Screen--*

FIG. 7. This shows how Newton obtained the spectrum

triangular piece of glass. Newton was the first man to
explain correctly how those colours were produced. As
a matter of fact, what he originally wanted to do was to
get rid of these colours. He was engaged in making a
telescope, and found that he could not make lenses which
would give clear images without coloured edges. He,
therefore, determined to find out just why the colours
were produced, so that he might see what he should
do to prevent their formation; to do this he devised
an experiment whereby he obtained the colours very
clearly.

Instead of a lens he used a triangular wedge of glass
called a 'prism.' First of all he made a small hole in

70 THE ROAD TO MODERN SCIENCE

the shutter of a darkened room, and allowed the narrow
beam of sunlight which came through the hole to fall on
a screen opposite (see diagram). Then he placed his
prism in between the hole and the spot of light on the
screen. He noticed two things. First, the spot of light
moved its position considerably; and secondly, instead
of being a circle of white light it became a band of
coloured light nearly five times longer than it was wide.
He examined the colours carefully, and found that there
were seven in all red, orange, yellow, green, blue,

FIG. 8. Here the colours are recombined to form white light

indigo, and violet. The red was nearest the original
position of the spot and the violet farthest away. Thus,
from his original white light Newton had separated out
seven different kinds of light. Later he found that if he
placed an exactly similar prism, only in a reversed position
from the first, in the path of the coloured rays (see
diagram), the rays recombined and formed a spot of
white light.

The explanation which Newton finally came to after a
variety of very careful experiments was that white light
is made of seven different kinds of coloured rays. When
these pass through a prism (or lens), each ray is bent,
but not to the same degree. The red is bent least and
the violet most, so that if the light coming from the prism

PLATE V

cu
o

<u

H

Si

Safe
O

w J 5

r^ ^ s

PLATE VI

Sir Isaac Newton

NEWTON, THE MASTER BUILDER 71

is caught on a screen, a band of colours is produced with
red at one end and violet at the other. Newton could
not see how he could prevent this happening with a lens
and get an image without coloured edges. He, therefore,
gave up the idea of using a lens and invented a new kind
of telescope, called the * reflecting telescope, ' in which
he used a curved mirror instead of one of the lenses which
Galileo had used in his telescope. Later, after Newton's
time, it was found that the colour could be got rid of by
making the lens of two different kinds of glass, so that,
nowadays, good telescopes can be made on Galileo's
pattern.

Now we come to the last and perhaps the most famous
piece of work which Newton carried out. This was con-
cerned chiefly with astronomy, although it necessarily
included a good deal of the branch of Physics which we
call ' dynamics/ i.e. the science of moving bodies. When
he got to Cambridge, one of the first books which Newton
read was that by Kepler, in which he proved that the
paths of the planets round the sun were ellipses. The
book greatly interested Newton, but he immediately
wanted to go further and know why the planets moved
in ellipses. He realised that there must be some force
pulling each planet towards the sun, for Galileo had
shown very clearly that if a body is moving it will
continue to move in a straight line until some force either
stops it or deflects it from that straight line. Since the
planets were continuously deflected from motion in a
straight line, and always towards the sun, it seemed
obvious that there must be a force pulling the planets
towards the sun. Newton also worked out by mathe-
matics that the planets would trace out those elliptical
paths if the force pulling them towards the sun varied

72 THE ROAD TO MODERN SCIENCE

inversely as the square of the distance between the planet
and the sun that is, if the force became very much
stronger the nearer the planet was to the sun. He was
much occupied with this problem in the year 1665, when
the University of Cambridge had been 'sent down'
because of the Great Plague. The story goes that he
was in the orchard at his home, turning the problem over
in his mind, when an apple fell to the ground just by him.
It flashed into his mind that here was a well-known
example of a body being pulled by a force which obeyed
that 'inverse square law' which he had worked out for
the planets. (It was Galileo who had shown that falling
bodies obey this law.) Now the apple was pulled towards
the earth, and the planets were pulled towards the sun,
but each according to the same law of force. Was it
possible that each was only an example of a more general
law by which all masses of matter were attracted to each
other ? If he were right, then he should be able to prove
it by finding whether the moon's attraction towards the
earth obeyed this law. He at once set about this new
problem. For it he needed the following items of
knowledge, all of which were available :

(1) The distance of the moon from the earth.

(2) The time taken by the moon to make one com-
plete revolution round the earth.

(3) The distance through which any body falls
towards the earth in one second.

Newton's task was to calculate from (i) and (2) how
far the moon moved towards the earth in one second.
This should agree with (3) if he were right in his idea.
Alas, he found that it did not, and so for the time being
he was obliged to abandon his theory ! A good many

NEWTON, THE MASTER BUILDER 73

years later, however, it was found that the distance of
the moon from the earth, which he had used, was in-
accurate. When Newton substituted the correct value
in his calculations he found that the ' fall ' of the moon
towards the earth every second was just what it was for
every other body attracted towards the earth. He had
been right after all !

FIG. 9. Mj, M ? > M 3 , M 4 are positions of the moon after
equal intervals of time. AM^ BM 3 , CM 4 show the moon's
'fall * towards the earth in each of these intervals

Let us see, now, just what Newton had done. First,
he had explained fully Kepler's laws about the motions
of planets, i.e. that there is a force pulling the planets
towards the sun; that this force grows proportionately
bigger as the square of the distance between the planet
and the sun gets smaller; and that the result of the
planets being pulled out of their straight-line path in this
way is that they move in ellipses. Secondly, he showed
that a force acts between all masses of matter and varies
according to the distance between them in exactly the
same way. The practical results of this ' Universal Law

74

THE ROAD TO MODERN SCIENCE

of Gravitation' are really very well known. In the
first place, all bodies above the earth which start from rest
fall straight towards the centre of the earth. Secondly,
if a body near the earth is moving relatively to it, for
example a ball thrown more or less horizontally, it will
trace out a particular kind of curve, called a parabola,
before it finally reaches the earth. (See diagram.)
Finally, if a body is moving sufficiently fast relatively to

FIG. 10. OS is the direction in which the ball is thrown ;
OABCD is the path along which it travels owing to the earth's
pull. PA, QB, RC, and SD show the total fall towards
the earth at the end of each of the first four seconds

another larger body, and is far enough away from the
latter, it will move continuously round the larger body
in a path which will either be a circle or an ellipse.
The path of the moon round the earth is very nearly a
circle.

Newton published the results of all his work in two
very important books, the Opticks and the Principia.
The latter is universally acknowledged to be the most
important book ever published in the history of
science.

As I have already said, Newton made clear the way for
the great army of scientists who came after him. Hence-

NEWTON, THE MASTER BUILDER 75

forth the account is not of one road but of the many tracks
comprising it. All lead towards the same goal that is,
to the complete understanding of ourselves and the world
in which we live. Travellers along each bring different
stories of their journeys to form separate chapters in the
great book of knowledge. Some of these stories will be
told in the second part of this book.

PLATE VII

O X
PBERT BOYL

The Hon. Robert Boyle

PART TI
CHAPTER X

Chemistry
i

THERE are to-day in Great Britain, in the various countries
of Europe, and in America, thousands of factories where
all the various things we use, and which form part of our
modern civilisation, are made. In almost every one of
these factories one or more of the great army of industrial
chemists is to be found at work in his laboratory. His
work may be merely to test the purity of the materials
which are being used and made in the factory; but more
often it is to experiment and try to find out new and better
materials or new and better ways of making them.

Every one of these chemists has been thoroughly
trained for his work. He may be trying to find something
new, but he knows how to set about it and is able to under-
stand and interpret the new results he gets from his
experiments. He is rather like a man with a very good
map, and a very good compass, setting out to explore new
country.

Now, rather under three hundred years ago there was
no map of this country at all. The old alchemists of the
Middle Ages had plenty to say about what they thought it
was like, but their experiments had only explored just the
outer fringe of it. Later, the followers of Paracelsus
penetrated a little further, but no one knew what the
country was really like.

77 6

78 THE ROAD TO MODERN SCIENCE

The Hon. Robert Boyle (1627-1692). Then, in the
seventeenth century, there came a man who at least put
forward a plan for exploring the unknown land of
chemistry. This man was the Hon. Robert Boyle, an
Englishman, born in 1627. His father was the great
Earl of Cork, and Robert was his seventh son. Boyle
lived through stirring times, for he was born in the reign
of Charles I ; lived through the Civil War and Cromwell's
rule, and saw the Restoration, the Great Plague, and the
Fire of London. He lived on through James ITs reign,
and died in 1692, three years after William and Mary came
to the throne.

He was at Eton as a boy, and then lived abroad with a
tutor for a good many years. While he was at Eton he
was made very ill by a wrong dose given by an apothecary.
This made him 'fear physicians more than the disease/
and he determined to gain for himself some knowledge of
medical drugs. When his father died he returned from
the Continent, and, having money and leisure, he devoted
himself for the rest of his life to scientific or, as they
were still called, 'philosophical' pursuits. It was about
this time that the famous Royal Society had its beginnings,
and Boyle was one of its earliest members. All the
results of his experiments were reported to this Society,
and in many of them he worked together with another
member called Hooke.

Boyle was a very careful experimenter, and he very soon
came to see that chemical knowledge, at that time, was
in a very muddled state and that most of the views held
had no foundation in fact. In 1661 he published his
famous book called the Sceptical Chymist, and it is largely
because of this book that he has been called by later
generations the 'Father of Modern Chemistry/ What

CHEMISTRY 79

is a Sceptical Chymist ? A sceptic is one who questions
everything and takes nothing for granted. This book of
Boyle's was written as a conversation between this
' Sceptical Chymist ' and two others. One of these was
an upholder of Aristotle and his four elements ; the other
of Paracelsus and his Three Principles, of which we heard
in Chapter VI, Part I.

In Boyle's book each of these two men in turn pro-
claims his beliefs and brings what evidence he can in
support of them. Then the sceptical chymist proceeds
to pull their arguments to pieces. Moreover, he describes
experiments which he has done himself which show that
there is no ground whatsoever for assuming that the
number of elements is either three or four. In fact, says
the sceptical chymist, it is quite impossible yet to fix a
limit to the number of substances which can be con-
sidered elementary. The thing to do, he says, is to stop
talking and repeating what somebody else has said, and
set to work to find out by experiment just what substances
are elements. By an element he explains that he means
a substance which cannot be split up into two or more
different parts.

Here, then, was a plan of action for the exploration of
the unknown country and it proved to be a very excellent
one. Actually Boyle himself did not add a great deal to
chemical knowledge ; most of his experiments concerned
physics rather than chemistry. What he did for chemistry
was to point out the only way which could lead to any
further advance into new territory. * Search for the
elements ' was his doctrine, and search by careful personal
observation and experiment. And for the next one
hundred and fifty years chemists both in England and on
the Continent carried on this search, until at the beginning

6*

8o THE ROAD TO MODERN SCIENCE

of the nineteenth century not three, nor four, but fifty
chemical elements were known, while to-day the number
is over ninety.

The Phlogiston Theory. In spite of Boyle's clear call
to action it was another hundred years before anything
much was achieved in this direction. In those days news
travelled slowly. You must not imagine that chemical
philosophers everywhere knew of Boyle's book and just
ignored it. It was a long time before it became generally
known. Besides, it did not contain many new and
exciting ideas ; it merely discredited the old ones in most
men's eyes. In the meantime a German chemist was teach-
ing some new ideas which caught the imagination of all
who heard of them, and quickly won many supporters.

These ideas concerned the age-old question of burning :

What does happen when anything burns ?

Why will some substances burn while others will not ?

The old idea was that * inflammable' substances con-
tained a lot of the fire element which could be seen
escaping in the flame. The new theory was really only
the old one in modern dress ; but in its new form there
certainly did seem quite a lot to be said for it.

This was the theory :

(1) All substances which would burn contained a
substance called Phlogiston, which was really the fire-
element under a new name.

(2) Substances, such as sulphur, which burnt very
easily were very rich in phlogiston.

(3) All metals which changed to a powder when
heated also contained phlogiston.

(The metals which do not change are gold and
silver.)

(4) When substances burn, or metals are heated so

CHEMISTRY 81

that they change to a powder (called a calx), phlogiston
always escapes. This means that the metal, before
heating, is made up of two different parts, the powder
or calx, and phlogiston. According to this theory,
then, a metal could not be one of the elements for
which Boyle had told chemists to look. In fact, no
substance which burnt could be an element.

This new teaching, known as the Phlogiston Theory,
was a great deal better than the old ones of the Middle
Ages or even that of Paracelsus. It was proved to be
wrong; but there was a great deal of evidence in its
support. Partly because of this, but also because during
that time there were no really great men interested in
chemistry, the Phlogiston Theory held the field for a
hundred years after the time of Boyle. Then, quite
suddenly, a tremendous advance was made along the way
directed by Boyle.

The start was made by three Englishmen living in the
latter part of the eighteenth century. Very different
were these three men. Dr Joseph Black was a learned
Edinburgh professor ; Dr Joseph Priestley was a fervent but
poor Unitarian Divine ; while the Hon. Henry Cavendish
was a wealthy nobleman, the grandson of a Duke on both
sides. All three, for the greater part of their lives, were
firm believers in the Phlogiston Theory.

Dr Joseph Black. Let us first take the work of Dr
Black. He was a doctor before he became a Professor
of Chemistry, so that he was interested in substances from
the point of view of their use in medicine. In this way
it happened that he made a new white solid, magnesia
alba, which he found was very like chalk.

Chalk, of course, had been known and used for a very
long time. The Romans used to heat chalk in kilns to

82 THE ROAE TO MODERN SCIENCE

get quick-lime which they used to make mortar. The
alchemists knew that when vinegar was added to chalk it
bubbled violently ; it effervesced, as we say now. Another
substance prepared from the ashes of a plant called ' kali '
also effervesced with vinegar; and from this plant all
substances behaving in this way took their name and were
called Alkalis.

Now an odd thing was found to happen if an alkali
was heated with quick-lime. Quick-lime was so called
because it would burn the skin quite badly, much as
would a live or quick coal. When quick-lime and an
alkali were heated together, this burning property was
passed on to the alkali. The latter now burnt the skin,
while the lime was quite mild and inoffensive and was, in
fact, once more chalk.

The obvious explanation at that time was that quick-
lime was made up of chalk and a fiery substance (phlogis-
ton) which had joined with the chalk during the heating of
the latter to make quick-lime. This fiery substance left
the quick-lime and joined with the alkali, when the two
were heated together. The new burning kind of alkali
was called a 'caustic alkali.' Both caustic alkali and
quick-lime, therefore, contained two substances according
to the old explanation :

Quick-lime = chalk + phlogiston.

Caustic alkali ordinary (or mild) alkali 4- phlogiston.

Chalk and ordinary alkali were, therefore, obviously
simpler substances than quick-lime and caustic alkali.

Dr Black found his new substance magnesia alba to be
like chalk and the alkalis because (i) it effervesced with
vinegar; (2) when heated with quick-lime it turned the
latter back to chalk.

CHEMISTRY 83

It was, in fact, a new mild alkali.

He next tried to find out whether, like chalk, it would
become * caustic ' or ' quick ' when it was heated strongly.
Before heating it, however, he did something which no
one had bothered to do before in this kind of experiment.
He weighed the magnesia alba which he was going to heat.
Sure enough, on being heated it turned into a substance
quite like quick-lime, though by no means so burning
in its properties. Then he weighed this new substance
and found that it only weighed y/iaths of the weight
of the original magnesia. What had happened to the
magnesia in the heating ?

To try to find the answer, Black made another experi-
ment. Vinegar, you remember, when added to the
original magnesia had caused a great deal of bubbling
or effervescence. He now added vinegar to this new
substance obtained by heating the magnesia. There was
no effervescence.

Black explained the result in this way. Since the
magnesia lost in weight when it was heated, something
had left it. Nothing could be seen leaving it, however.
Now the only thing which Black could think of which
could leave a substance without being seen was air, so
that he came to the conclusion that some kind of 'air,'
which was originally contained in the magnesia, left it
when it was heated. This conclusion was borne out by
his experiment with the vinegar. When vinegar is added
to magnesia before it is heated, the effervescence caused
must be due to bubbles of this air leaving the magnesia.
Since heated magnesia gives no effervescence, the ' air '
must already have been driven off by the heating.

Black's next idea was to try to get this ' air ' back into
the heated, or caustic, magnesia and so form his original

84 THE ROAD TO MODERN SCIENCE

magnesia alba again. Now, since mild alkali also
effervesced with acids he thought this probably contained
the same kind of air ; so he dissolved some heated magnesia
in acid and then added mild alkali. From this he got a
solid substance, just like his original magnesia alba,
which effervesced with acids. The mild alkali had given
the 'air' which it contained to the caustic magnesia,
forming again the magnesia alba.

Having found out all this about magnesia alba which
was so like chalk, Black obviously was led to try the
experiments with chalk and see if he got the same results.
He did in every respect, (i) Chalk also lost weight
when heated to make quick-lime.* (2) Quick-lime did
not effervesce with vinegar.

The same explanation, therefore, also applied to chalk.
That is to say, chalk contained 'air' which could be driven
off, either by heating, or by adding acid :

Chalk = quick-lime + ' air/

According to Black, therefore, quick-lime is a simpler
substance than chalk. The old idea had been the other
way round.

Arguing in the same way, Black showed also that the
caustic alkalis were simpler substances than the mild
alkalis, which could be shown to contain 'air' because
they effervesced with acids.

This 'air' which is contained or 'fixed' in magnesia,
chalk, and the mild alkalis, Black called Fixed Air. It
is what we now name Carbon Dioxide. He was never
able to collect any large quantity of it, but he showed how
it could be distinguished from ordinary air and its presence
recognised. Quick-lime, although nearly insoluble, will
dissolve to a certain extent in water and its solution is

CHEMISTRY 85

called lime water. In ordinary air, lime water remains
clear, but a trace of Black's fixed air turns it milky. By
using this test Black showed that

(1) The air which we breathe out contains fixed air;

(2) Any sugary liquid which is fermenting to form
beer, wine, or an alcoholic liquor gives off fixed air;
and

(3) That charcoal when it burns also forms fixed air.

We must now sum up the important points of Black's
work.

1 . He showed that the old idea that chalk and the mild
alkalis were simpler substances than quick-lime and the
caustic alkalis was wrong, since the former substances
could be shown to consist of the latter joined with fixed
air. For some years it was thought that the caustic
alkalis and quick-lime were probably 'elements/ since
all efforts to decompose them failed. We shall hear
later how their decomposition was brought about by
using an electric current.

2. He discovered a new kind of air, fixed air. This
was the first time anyone had really recognised a kind of
air distinct from common air. Priestley followed up
this part of his work with very great success.

3. Finally, and most important of all, for the first time
he weighed the substances with which he worked and
drew his conclusions from the results of these weighings.
If a substance weighs less than the one from which it
was made it must be a simpler substance (provided
always, of course, that the person who does the weighing
is known to be careful and accurate 1).

Joseph Priestley (1733-1804). Both the other members
of this famous trio of British chemists were extremely

86 THE R6AD TO MODERN SCIENCE

interesting characters. Joseph Priestley was born near
Leeds in 1733 of quite poor parents. He was brought
up very strictly and trained to be a Nonconformist
Minister. He was not very popular with the people of
his first chapel and turned to teaching instead. Soon
after he married, he met a man named Benjamin Franklin,
whom we shall hear of again for his discoveries in elec-
tricity. This friendship turned Priestley's interest to
scientific subjects, and he started experiments on his
own with such success that he was soon made a Fellow
of the Royal Society. After an interval, in charge of
another chapel, Priestley became librarian to the Earl of
Shelburne, and then had much mofe time and leisure for
his favourite hobby. Here he wrote many treatises on
his scientific work and also a great many theological
tracts. These latter were of a somewhat unorthodox
nature and violent in tone, and he was eventually obliged
to leave the Earl of Shelburne and take charge of a chapel
in Birmingham. Here once again he got into trouble;
this time because of his sympathies with the Revolution
which had broken out in France. An angry mob stormed
his house and destroyed much of his property, and he
was forced to flee, first to London and eventually to
America, where he died in 1809.

The Hon. Henry Cavendish. The Hon. Henry Caven-
dish was a man of very different nature. He was very
wealthy, and owned two or three houses in London, each
devoted almost entirely to his scientific pursuits. He
hated society, and rarely went out, except to the regular
dinners and meetings of the Royal Society Club. He had
a horror of women, and, it is said, would not have one in
his house even as housekeeper.

His scientific achievements were by no means limited

PLATE VIII

G

<u

rt

U
fr

G

U

EC
o

a

u

H

O
rt

5
I

C/3

O

PT.ATK TX

Dr Joseph Priestley and his Pneumatic Trough

CHEMISTRY 87

to chemistry. In the study of electricity, and in most
other branches of physics, his name occurs as one of the
great early investigators. His passion was to measure
everything, and because of this he ranks with Black as
one of the great pioneers of the new era.

In the story of chemistry the names of Cavendish and
Priestley are linked with two great pieces of work. In
each of these one of the original ' elements ' of Aristotle
is shown to be, after all, not a single simple substance.
The first of these was air. Here both men played a
part. The second was water, and here the work was
carried out almost entirely by Cavendish.

New Kinds of Air. Until the time of Boyle there was
thought to be only one kind of air the common air which
is all about us. True, that air often seemed to change
in some of its qualities, more especially in the matter
of smell ; but this was always put down to the presence
of impurities with which it had become impregnated.
Boyle, in one of his experiments, found that when iron
dissolved in an acid substance, called oil of vitrol, there
was a great deal of effervescence, and the air which came
off would burn if a candle were held to it. Boyle must
have realised that this air was not the same as ordinary
air, but, as far as we know, he did not say so. As we have
seen, it was Black who first recognised that there might
be different kinds of air.

One of the first pieces of work carried out by Cavendish
was to show quite clearly that Boyle's 'inflammable air'
and Black's 'fixed air' really were completely different
substances from ordinary common air. This he was
able to do by measurement with weighed bladders filled
with each kind of air in turn. He found that the in-
flammable air was only i /nth of the weight of the same

88 THE ROAD TO MODERN SCIENCE

volume of common air ; while ' fixed air ' was more than
one and a half times as heavy. Here, again, we see how
important it was to get the weights of substances and how
clearly the results showed up directly they were obtained.

You will remember that Black found that his 'fixed
air' was given off from a fermenting liquid. Priestley's
interest was turned to the subject by the presence, near
his house in Leeds, of a brewery, so that a plentiful supply
of this fixed air was available. He did not learn a great
deal more about this gas than did Black, although, in-
cidentally, he discovered how to make 'soda-water' by
forcing it into water.

Priestley is famous for the apparatus he devised to
collect these new airs. He made them displace water
or mercury from jars inverted in a big trough of the
liquid. This he called a pneumatic trough, from the
Greek word 'pneuma,' meaning air. Gases which do
not dissolve in water are always collected in this way
now. Priestley generally used mercury rather than
water. (See Plate IX.)

After making fixed air and inflammable air by the same
methods as Cavendish had used, Priestley then tried to
make further new airs by mixing other metals with other
acids. An acid is a substance which, like vinegar, makes
chalk effervesce and which turns a certain purple sub-
stance, called litmus, red. He also tried heating a variety
of solid substances strongly to see if he could get a gas.
As a result of a number of experiments he succeeded
in obtaining several new gases or 'airs/ These were
what we now call the three oxides of nitrogen, hydrogen-
chloride, and ammonia. The two latter he called marine
acid gas and alkaline air.

His most famous discovery, however, was that of the

CHEMISTRY 85

gas which is now called oxygen, but which he called
* dephlogisticated air.' He had procured a new and large
magnifying or 'burning' glass which he used to heat
substances. He did this by focussing on them the sun's
rays through the glass. The substance was enclosed in a
bottle of mercury inverted in a trough of the same liquid,
One of the substances which he heated was the red powder
got by heating mercury for a long time in air. This was
known as Red Mercury Calx. To his great delight
Priestley found that an air (or gas *) was very readily
expelled from this substance which, at the same time,
again formed mercury. He collected several jars of the
gas and set about examining its properties in the ways
he usually employed. To begin with, he found that a
candle burnt in it very brightly indeed, far more so than
in common air; while a piece of glowing wood sparkled
and flared and burnt away completely. A mouse placed
under a vessel filled with this new gas lived twice as long
as it would have done if the jar had been filled with
ordinary air. Priestley himself, on breathing the air,
fancied that his ' breast felt peculiarly light and easy for
some time afterwards.'

Priestley was a very firm believer in the Phlogiston
Theory and always tried to explain his experiments in its
light. A candle, if placed in a closed vessel, will burn for
a little while and then go out; even though there is
plenty of candle left to burn. According to the Phlogiston
Theory the explanation of this was that the air could only
hold a certain amount of phlogiston. Once the air was
saturated nothing could burn in it, since burning was
always accompanied by the giving off of phlogiston.

1 The term * gas ' was introduced quite soon and the word ' air *
kept to denote ordinary atmospheric air.

90 THE ROAD TO MODERN SCIENCE

Priestley explained the extraordinary ease with which sub-
stances burnt in his new air by supposing that it contained
absolutely no phlogiston itself. It, therefore, took up
the phlogiston of burning substances very readily. On
the other hand, he said, common air must contain some
phlogiston since it required a much shorter time to
become saturated. The new gas was, therefore, common
air without phlogiston, or * dephlogisticated ' air.

So we see that Cavendish and Priestley showed quite
clearly that common air is by no means the only kind,
but that a number of totally distinct airs exist. As we
have said, these are now known as gases.

The Compound Nature of Water. Both Cavendish and
Priestley were interested in the new science of electricity
and each possessed a machine for making electric sparks.
Priestley one day thought he would try the effect of send-
ing a spark through a mixture of inflammable air and
common air. He found that after the spark a kind of
dew had formed on the walls of the vessel. Cavendish
heard of this experiment and repeated it on a larger scale.
Instead of common air, however, he used the new
dephlogisticated air (oxygen). By using large quantities
and sending repeated sparks Cavendish was able to collect
a fair amount of the dew which Priestley had noticed.
He tested this in every way he could think of, and came to
the conclusion that it was pure water. Water then could
not be a simple elementary substance since it was made
from two different substances :

Water inflammable air + dephlogisticated air.

(hydrogen) (oxygen)

So yet another of Aristotle's elements was proved to be no
element at all !

CHEMISTRY 91

II

Lavoisier (1743-1794). While these three great
chemists, Black, Cavendish, and Priestley, were carrying
on their investigations in England, there was living in
France a man who was destined to do even greater things
for chemistry. This man was Jean Antoine Lavoisier.
He was born in 1743 of middle-class parents and received
a very good education. At first he studied law, but soon
the attraction of mathematics and physical science made
him decide to devote himself entirely to their study.
Quite early his work gained for him admission to the
French Academic des Sciences, which is the equivalent
of the Royal Society in England. When he was about
twenty-six, he decided that, to carry out his one aim in
life, which was the advancement of science, he needed a
larger income than that derived from his small private
fortune. To this end he took a step which eventually
brought his brilliant career to an untimely end.

There was in France, during that time of oppression
preceding the Revolution, a financial company known as
the * Ferme General, * which undertook to collect for the
government all kinds of taxes and duties on various com-
modities. Lavoisier, in order to increase his income,
became a member of this company. There is no doubt
that a great deal of corruption and oppression accom-
panied this collection of taxes, and many of the company's
agents did very well for themselves out of it. Later,
when the Revolution came, it is hardly surprising that its
members came in for their share of unpopularity. It is
quite certain, however, that Lavoisier invariably carried
out his duties in an entirely honourable manner ; in fact,
he did all in his power to remove many of the obvious

92 THE ROAD TO MODERN SCIENCE

abuses. Nevertheless, the temper of the revolutionaries
was not such as to distinguish between individuals where
the records of the company as a whole were so black. We
are, however, anticipating.

There were some twenty years between Lavoisier's
appointment as a fermier general and the outbreak of
Revolution. It was during these years that his greatest
work was done. In 1771 he married a very charming
and intelligent young wife, who helped him in his work.
When he published his famous book, Traiti de Chimie, it
was she who made the plates for the book. In each of the
two well-known pictures of Lavoisier in his laboratory
his wife is also to be seen.

Like nearly all famous men, Lavoisier had jealous
enemies. It was these enemies who, during the Revolu-
;ion, helped to pile up false evidence against him. In
[791, two years after the storming of the Bastille, he was
irrested and condemned to the guillotine. A plea was
jut forward that as a scientist employed, as he was then,
m public work in connection with weights and measures,
i reprieve should be granted. Then came the often
juoted reply: 'La Republique n'a pas besoin de
;avants, il faut que la justice suive son course/ (' The
Republic has no need of learned men, justice must follow
icr course.') Lavoisier was, therefore, beheaded. 'A
noment was all that was necessary in which to strike off
lis head, and probably a hundred years will not be
ufficient to produce another like it/ So said another
amous scientist, and perhaps he was not far wrong.

Before describing his actual experiments we will sum
ip briefly those achievements of Lavoisier which were the
ause of such high praise from one of his own time.

i. He showed clearly that the old Phlogiston Theory

CHEMISTRY 93

of burning was all wrong. In its place he put forward a
new one which was so obviously right that all the chemists
of the time (with the exception of Priestley) eventually
came over to his way of thinking.

2. He drew up a list of about thirty substances which
he considered to be elements, putting them into three
classes according to their chemical behaviour with each
other.

It is undoubtedly the first of these for which he is most
famous ; but the second was very important, for it tidied
up prevailing ideas and enabled chemists to take stock
of their knowledge. We might perhaps describe it as the
first sketch map which was made of the new country which
was being explored.

Now let us turn to the first achievement and see how it
was accomplished. At once it must be emphasised that
Lavoisier's success was due above all to the fact that at
every step of the way he measured the quantities of the
substances with which he was working. This he did
either by weighing them or by measuring their volumes.

We will begin with some experiments which Lavoisier
did before Priestley discovered that wonderful new gas
' dephlogisticated air/ or oxygen as Lavoisier was to call it.
First, as the result of a great many experiments, he
established the following facts :

(1) A metal increases in weight when it is heated to
form a calx. (This was not new knowledge, but a
fact of which little notice had been taken.)

(2) Sulphur and phosphorus (which are not metals)
also increase in weight when they are burnt.

(3) When phosphorus is burnt in a limited supply
of air, part, but only part, of the air disappears. The
remaining air will not allow the rest of the phosphorus

94 THE ROAD TO MODERN SCIENCE

to burn, and also puts out the flame of a candle.
(This is the famous 'Bell-Jar' experiment which
everyone who has done any chemistry at all will have
seen performed.)

At this stage Lavoisier heard of Priestley's discovery.
There is no doubt that he thereupon saw immediately
the true explanation of the facts ; if, indeed, he had not

FIG. n. Lavoisier's experiment to prove his theory of
burning. A, retort containing mercury heated by charcoal
furnace (D). B, Bell jar in trough of mercury (C)

already done so. He at once devised the following ex-
periment which should make it absolutely clear to every-
one that his ideas were right :

(1) He took a retort with the neck bent up at the
end, as shown in the diagram, and in it he placed
4 ounces of pure mercury.

(2) He placed the retort with the end of the neck
leading into a bell jar inverted over mercury (see
diagram). The total volume of air enclosed in the
retort and the bell jar together was 50 cu. ins.

(3) He heated the retort for twelve days. During

CHEMISTRY 95

that time a red scale (Priestley's red mercury calx)
formed on the mercury.

(4) The mercury meanwhile had risen in the bell
jar, reducing the volume of air to 42 cu. ins., i.e.
8 cu. ins. of air had disappeared.

(5) He collected the red mercury calx and weighed
it. It weighed 45 grains.

(6) He put this red mercury calx into a small retort
and heated it, collecting the gas evolved in the usual
way. In this way he obtained 41 \ grains of mercury
and 8 cu. ins. of air which, on testing, he found to be
identical with Priestley's dephlogisticated air.

Note. The 8 cu. ins. of air, which had disappeared
during stage 4, had now been regained and found to be
this new gas.

(7) He was able to calculate the weight of the 8
cu. ins. of gas, when he had found its density, and this
was exactly equal to the weight lost by the red mercury
calx when it was heated, i.e. 3 J grains.

What now was this new theory of burning which these
experiments proved? First, common air is made up of
two different gases ; an active one which Lavoisier called
Oxygen; and an inactive one which he called Azote.
Secondly, when anything burns in air, the oxygen joins
with the thing which is burning to form the new sub-
stance. In the case of a metal the calx is formed. The
calx of a metal, therefore, is not simpler than the metal,
but consists of the metal joined to oxygen. The metal
is the simple substance. This is a very simple explana-
tion, as you see, and its great merit is that it explains all
the facts; not a single fact to do with burning has ever
been found which does not fit in with this theory.

Priestley discovered a great many new gases, as we have
seen, and named them. But, being a firm believer in the

96 THE ROAD TO MODERN SCIENCE

Phlogiston Theory, many of the names Priestley gave to
these gases did not mean anything in the light of the new
theory. One of the things Lavoisier did in the general
tidying up was to give appropriate names to the many
new substances which had been discovered. He also re-
named most of the old ones to fit into his general scheme.
Hydrogen was so called because it produced water;
azote means inactive. In England we now call this last
gas nitrogen, but it is still called azote in France. Nearly
all the names of chemical substances which are now met
with in chemistry were originally given by Lavoisier. He
made one mistake. Oxygen had proved to be such an
important gas in connection with burning, that Lavoisier
was led to overestimate its importance as a whole. He
was convinced that oxygen was to be found as the essential
element in all acid substances. The name oxygen, which
he gave it, means 'acid producer.' It is now known that
all acids do not contain oxygen. Moreover, it has been
found that it is hydrogen that is the element common to
all acids. All the same, this mistake is almost the only
one that we can hold up against Lavoisier. He was a very
great scientist.

Finally, Lavoisier drew up a list of those substances
which, so far, had resisted all attempts to split them into
simpler parts and which, therefore, for the meantime at
any rate, might be called elements. Here are some of the
substances which he included in his list :

Light Sulphur

Heat Phosphorus

Oxygen Carbon

Azote Lime

Hydrogen Magnesia

All the metals.

PLATE X

2

2 1

o ^

c S

'Si

CHEMISTRY 97

Notice that he did not include the caustic alkalis although
he did include lime. The caustic alkalis had not yet been
split up, but Lavoisier thought it very probable that they
were not elements.

Of the four men of whom we have been speaking,
Black, Cavendish, and Priestley lived in the same country,
while Lavoisier in Paris was not so very far away. The
first three were members of the Royal Society, and the
latter of the French Academic des Sciences, so that their
work was well known. Though communication between
them was by no means so easy and so frequent as between
scientists of to-day, they were each fairly well informed
of the work of the others. As we have seen, early experi-
ments by Priestley were the starting-point of Cavendish's
great work on the composition of water; and his dis-
covery of oxygen gave Lavoisier just that bit of informa-
tion he needed to make his theory of combustion complete.

Karl Wilhelm Scheele (1742-1786). While these more
famous chemists were making and publishing their dis-
coveries in England and France, farther away, in Sweden,
a poor apothecary, Karl Wilhelm Scheele, was working on
much the same lines and obtained independently many of
these results. He actually prepared oxygen two years
before Priestley carried out his famous experiment (1774),
but was not able to publish his work until 1777. It was
not until that year that he heard of Priestley's experiment.
Scheele was, therefore, the true discoverer of oxygen,
although Priestley's name is inseparably connected with
it. Because of his struggles with poverty and ill-health
the real merit of Scheele's work was not made known to
the world until considerably later, so that he influenced
less than his contemporaries the immediate future of

7

98 THE ROAD TO MODERN SCIENCE

chemistry. Nevertheless, his contribution was worthy
of great respect, and his name must not be forgotten. In
addition to his discovery of oxygen he also discovered
that very remarkable green gas, chlorine. He isolated
a great number of acids which occur in various plants
and fruits, and are known as 'vegetable acids/ Besides
this he did a great deal more work which proved to be of
the greatest value to building up the science of chemistry ;
though to enumerate the various discoveries would
convey little to you now. Only towards the end of his
life did he receive the recognition he deserved. We
know that he was then in communication with Lavoisier.
Unfortunately his health was very bad, probably because
of his early privations; and in 1786 he died at the com-
paratively early age of forty-four.

Sir Humphry Davy (1778-1829). Lavoisier, in setting
out his list of those substances which he considered to be
elements, had summed up and rounded off the work of
the previous one hundred and fifty years which had been
initiated by Boyle. Most of the substances in his list
are still classed as elements, but a few had to be removed
and many more added during the next hundred years.
The man who did most towards correcting Lavoisier's
list was Sir Humphry Davy, a popular and successful
English chemist. Davy was a Cornishman, born in
Penzance in 1778. He was a boy of sixteen at the time
of Lavoisier's death. In the following year he was ap-
prenticed to a surgeon and apothecary in Penzance and
began studying for the medical profession. He was at
this time a great reader of a variety of subjects, and was
not afraid to wield his own pen both in prose and verse.
In 1797 he read a copy of Lavoisier's famous book on
chemistry, which so fired his enthusiasm that he began

CHEMISTRY 99

making experiments of his own with such materials as
were available in the surgery. His work at that time led
to nothing of great note, but the essays which he pub-
lished on it brought about his appointment to the
Pneumatic Institution at Bristol. Here the effect of the
many new gases which had recently been discovered
were being tried on invalids in the hope of effecting cures.
This appointment gave Davy far more opportunity for
his own experiments and he soon gained a name for
himself in the scientific world. It was here he discovered
the peculiar properties of one of the gases discovered by
Priestley which enabled it to be used as an anaesthetic.
This is the familiar * Dentists' gas' still used to-day.

Meanwhile, in London, the efforts of a certain Count
Rumford (who, a little later, married Lavoisier's widow)
had led to the establishment of the Royal Philosophical
Institution. This was designed to help scientific re-
search, and also to provide lectures for the general public
on the discoveries which were made. These lectures are
still continued to this day. All branches of science were
to be represented, and in 1801 Davy was invited to
become assistant-lecturer and experimenter in chemistry.
He was then twenty-three years old. The whole of the
rest of his life was spent in connection with the Royal
Institution. Fame and honours came quickly, and he
was soon a popular member of London society. In 1811
he became Sir Humphry Davy, and almost at the same
time he married a wealthy widow who made his position
in society still more secure. Two years later, in spite
of the fact that England and France were at war, he
obtained permission from both governments to travel
on the Continent with his wife and his laboratory assistant,
young Michael Faraday, of whom we shall hear more

ioo THE ROAD TO MODERN SCIENCE

later. There were, both in France and Italy at that time,
a number of very famous men working in all branches of
science. During his tour Davy visited almost all of
them, exchanging views and often continuing his own
work in their laboratories.

Soon after his return to London, Davy investigated the
cause of the serious explosions which were then con-
tinually occurring in coal mines. As a result he invented
the famous * safety lamp' which afterwards always went
by his name. This won him a very handsome gift from
the colliery owners, and in 1818 he was made a baronet.
Two years later he was elected President of the Royal
Society, and continued to hold the office for the next
seven years. His health then began to decline, and he
spent much time in the south of Europe, still carrying on
his experiments. He died abroad in 1829.

Davy's researches were not limited to chemistry, but
it is his chemical discoveries for which he is most famous
and with which we are now concerned. Lavoisier,
mistakenly as it turned out, thought that all acids con-
tained oxygen as the acidifying principle. Scheele
had discovered the gas chlorine, and another French
chemist, Berthollet, had shown that chlorine was present,
combined with hydrogen, in the acid which was then
known as muriatic or marine acid, because it was made
from salt. We now call it hydrochloric acid. Because
of this fixed idea of his, Lavoisier felt sure that chlorine
must contain oxygen. Instead of putting chlorine itself
in his list of elements he predicted that when chlorine
could be decomposed a new element would be found
combined with oxygen. But in spite of all the efforts
of a number of chemists chlorine stubbornly refused to
yield either oxygen or a new substance; it would not

CHEMISTRY 101

be decomposed. Davy, in his turn, carried out all the
experiments he could devise, and finally announced it
as his opinion that chlorine could not be decomposed
and was, in fact, itself an element. This obviously meant
that Lavoisier was wrong in his theory that all acids
contained oxygen, since one of the commonest acids
contained only two elements, hydrogen and chlorine,
and no oxygen.

Davy was also concerned in the discovery of iodine
and its classification as an element. He recognised its
similarity to chlorine, and predicted that another similar
element, fluorine, would be discovered from an acid
which he had isolated and which was very like hydro-
chloric acid. Fluorine was later isolated, and also another
element, bromine, which, together with chlorine and
iodine, make up the 'Halogen Family.'

Although the caustic alkalis, which Black had shown
to be simpler than the mild alkalis or carbonates, had
not been decomposed into any still simpler substances,
Lavoisier did not believe that they were elements and did
not include them in his list. He did, however, include
quick-lime and four other similar substances known as
earths. Perhaps Davy's most famous achievement was
the decomposition of all except two of these substances.
He had at his command, however, an aid which was not
available to earlier chemists.

In 1790 the Italian scientist Volta made his famous
voltaic pile from which a continuous electric current
could be obtained. Some years later two English
chemists found that the current could be sent through
water. In doing so, however, they found that it de-
composed the water into its elements, hydrogen and
oxygen. The latter was given off in bubbles at the wire

102 THE ROAD TO MODERN SCIENCE

where the current entered, and the former at the wire
by which the current left the water. Gases had already
been decomposed by an electric spark; here was a way
of decomposing liquids.

On arriving at the Royal Institution in 1801 Davy at
once constructed a battery and set about investigating
this newly discovered decomposing power of an electric
current. It was not, however, until 1807 tiiat he made
any outstanding discovery. First of all he tried passing
the current through strong solutions of caustic alkalis.
He only succeeded in decomposing the water of the
solution; that is, he only got hydrogen and oxygen.
Then he passed the current through melted caustic potash
alone. He was evidently on the right track this time,
for he got an intense light and a column of flame at one
wire. He guessed that he was getting something new,
but that the new substance caught fire at the temperature
at which he was working. He, therefore, decided not
to melt the potash first but to let the current do the melt-
ing. After that he was successful. Where the negative
wire (where the current left) touched the potash, small
globules of a shiny metallic substance collected. Some
of these still burnt with a bright flame as soon as they
were formed. He examined this new substance very
carefully and came to the conclusion that, although in
many respects it was unlike the better-known metals,
yet it undoubtedly was a new metal. He gave it the
name Potassium. Similar experiments with caustic
soda, quick-lime, and the earths known as magnesia and
baryta, resulted in the discovery of the new metals,
sodium, calcium, magnesium, and barium. All of these
had to be added to the list of elements, while lime and
the earths had to be removed.

CHEMISTRY 103

III

Chemical Theory. The work of Davy may be said to
close a chapter in the history of chemistry. The majority
of the elements had now been identified ; and the possible
methods of decomposing substance all more or less in-
vestigated. Meanwhile a new chapter was opening.
The elements themselves having been determined,
chemists began to inquire how and according to what
rules they combined together to form compounds. Now
a plan of action is always imperative in order that a
real advance may be made. All scientific inquiry nowa-
days proceeds according to a well- recognised plan.

Firstly, all the known facts that can have any bearing
on the question are collected together and reviewed.
Secondly, a theory is invented which will explain all
the known facts; this is generally called an hypothesis.
Thirdly, assuming the hypothesis to be true, it is then
seen what new results should follow from the theory.
Lastly, experiments are then devised which should give
these results if the hypothesis is a true one. The more
conclusions that are supported by experiment the more
likely is the hypothesis to be true. One contrary fact,
however, must lead, if not to a new hypothesis, at any
rate to a revision of the old one.

In the investigation which forms the subject-matter of
this new chapter in the history of chemistry, the facts to
be reviewed were, for the most part, supplied by those
chemists whose work we have so far discussed. The
theory which was to explain these facts was produced by
an English chemist named John Dalton, while the further
experimental evidence necessary to establish the theory
was gained by a group of brilliant Frenchmen, the direct

104 THE ROAD TO MODERN SCIENCE

successors of Lavoisier, and by a very eminent Swedish
chemist, Berzelius.

The famous Atomic Theory of Dalton has proved to be
one of the most successful and comprehensive scientific
theories ever put forward. So much evidence has
accumulated in its favour during the years which have
elapsed since it was first advanced that it has acquired
almost the certainty of fact.

Law of Conservation of Mass. First of all let us see
what were the chief facts which Dalton had to explain by
his theory. Since Black first laid such stress on the im-
portance of weight in his experiments, all chemists had
tacitly assumed that during a chemical reaction the sum
of the weights of the reacting substances was always equal
to the sum of the weights of the products. In other
words, although the original substances apparently dis-
appeared and new ones took their place, the weight of
matter always remained the same. Lavoisier did very
careful experiments to show that this really was so and that
no matter was lost. This principle is generally known as
the * Law of Conservation of Mass, ' and is stated thus :
Matter can neither be created nor destroyed.

Law of Constant Proportions. Just before Dalton put
forward his theory, a great controversy had been going on
between two French chemists, Proust and Berthollet.
The question at issue was whether a compound, such as
iron sulphide, which was known to consist of the elements
iron and sulphur, always contained those elements in the
same proportion by weight. Proust said 'Yes'; while
Berthollet said * No, it all depends on the proportions in
which they are mixed before combination takes place/
Each, of course, brought forward evidence in favour of his

CHEMISTRY 105

view, but in the end Proust won, and his view was generally
accepted. This became known as the ' Law of Constant
Proportions,' and stated that:

Every compound contains the same elements combined
together in fixed proportions by weight.

Dalton's Atomic Theory. Now we come to Dalton's
atomic theory. The conclusions he arrived at may be set
out in five points :

(1) All matter is composed of small particles called
atoms, which are indivisible.

(2) An element is made up of atoms which are all
exactly alike in every respect. This means that they
have all the same weight. This weight is different
from the weight of the atom of any other element.

(3) Atoms can neither be created nor destroyed.

(4) The atoms of elements join together in small
whole numbers to form compound atoms (or molecules).

(5) The molecules of any one compound are alike in
every respect, and differ from the molecules of every
other compound.

Careful thought will show that point 3 explains the Law
of Conservation of Mass and points 4 and 5 the Law of
Fixed Proportions.

This theory of Dalton's is, of course, by no means new.
Originating with the Greeks, the conception of the atomic
structure of matter is one of the oldest in existence, and
Dalton knew it. Moreover, it was the theory which both
Boyle and Newton used constantly to explain and picture
to themselves the inner workings of things. The practical
value of Dalton's version of the theory was that he put it

io6 THE ROAD TO MODERN SCIENCE

in such a way that deductions could be made from it
which could be tested by experiment. There is no need
to go into details. The various laws of chemical com-
bination can all be deduced from the Atomic Theory, and
the majority were shown to hold good experimentally by
that group of French chemists already mentioned.

Atomic and Molecular Weights. Dalton had laid stress
on the point that the weight of its atom was a very
characteristic property of an element. An atom cannot
be seen even with the most powerful magnifying apparatus
invented, and it is obviously impossible to weigh an in-
dividual atom, although its weight has lately been cal-
culated. Realising this, the chemists of the last century
set out to find only the relative weights of the atoms.
Hydrogen was the lightest substance known, so that the
weight of its atom was taken as unity, and the atomic
weight of an element defined as the number of times
heavier its atomwasthan an atom of hydrogen. Similarly,
the molecular weight of an element or compound is the
number of times heavier its molecule is than an atom of
hydrogen.

For the next sixty years chemists all over Europe were
occupied in devising ways of determining molecular and
atomic weights and setting up an accurate table of these
weights. The man who led the way was the great
Swedish chemist, Berzelius. To him also we owe the
system of chemical symbols, formulae, and equation which
is such a bugbear to so many beginners in chemistry, but
such a boon when once mastered !

Classification of the Elements. The result of the sixty
years' work was that, the atomic weights of the various
elements having been determined, a complete scheme of
classification was possible simply by arranging the elements

CHEMISTRY 107

in the order of their atomic weights in rows of eight. In
this way it was found that all the elements in the same
family, such as the halogens, came in the same vertical
row, with the active metals on the left, and the active non-
metals on the right. A great variety of other points of
resemblance and difference were also brought out which
it is quite impossible to enlarge upon. The point to be
emphasised is that here at last was a complete and
accurate map. This was the result of the careful and
ordered exploration of the unknown country which had
been projected by Robert Boyle. How it would have
delighted him to see the fruit of his labours !

Although this seems a fitting end we cannot leave the
story here, but must go back and see how one portion of
this country at first seemed to defy all efforts at explora-
tion. Once penetrated, however, it proved to be a
veritable storehouse of untold wealth.

Rise of Organic Chemistry. The chemists of the
eighteenth century distinguished between two classes of
substances, those found in inanimate nature and those
derived from living tissues, either vegetable or animal.
The former are commonly known as inorganic substances
and the latter as organic. Inorganic substances were
comparatively easy both to analyse and synthesise (that
is, build up from their elements) once the general methods
of procedure had been mastered ; but organic substances,
while easily analysed, for a long time resisted all attempts
to synthesise them.

Scheele isolated and examined a large number of
vegetable acids, as we have seen; Lavoisier analysed
alcohol and showed how it was produced by fermentation
from sugar. A few years later it was established that the
majority of organic compounds, such as alcohol, sugar,

io8 THE ROAD TO MODERN SCIENCE

ether, oils, fats, and the vegetable' acids, all contained
carbon and hydrogen with a varying amount of oxygen.
It was generally thought, however, that some vital, or ' life/
force was necessary to make these substances, and that
they could never be made in the chemist's laboratory.
This belief was shattered in 1828, when a German chemist,
Wohler, prepared from inorganic materials a well-known
organic substance. This was urea, a substance found in
urine. This achievement opened up new vistas, and a
number of chemists devoted themselves entirely to the
study of organic chemistry. The chief fact which
emerged as a result of this investigation was that the
molecules of organic compounds . are extremely com-
plicated and contain a great number of atoms. That is
why, of course, it is so much more difficult to build them
up from their elements. To take sugar as a common and
comparatively simple organic substance, it was found that
its molecule contained twelve carbon atoms, twenty-two
hydrogen atoms, and eleven oxygen atoms !

The next thing to be found out was that the skeleton
of the molecule of every organic substance was made of
carbon atoms, with the oxygen and hydrogen hung on
outside, as it were. The carbon atoms might be in open
chains or in closed rings. The benzene molecule con-
sists of a ring of six carbon atoms each with a hydrogen
atom attached; naphthalene, of which you may have
heard, contains two such rings stuck together, while others
even have three rings. Occasionally an atom of nitrogen
is found in the ring as well. It was very soon found that
it was the hydrogen or oxygen atoms hanging on the
outside of these rings or chains that gave the substance
its special properties. Thus all the compounds with
a straight chain of carbon atoms and only hydrogen

CHEMISTRY 109

attached to the chain are very much alike, and as a matter
of fact form the mixture of substances in crude petroleum.
If there are not many carbon atoms in the chain the result
is a light inflammable liquid such as petrol, but a great
many carbon atoms give rise to solid paraffin wax.
Methods were soon devised for changing the hydrogen
atoms for those of other elements or groups of elements
well known in inorganic chemistry. You will see at once
the immense possibilities opened up. New organic
compounds (or carbon compounds as they should be

A o ffr co

V' c vv c

FIG. 12. Showing the rings of carbon atoms in the mole-
cules of benzene and naphthalene, with the simple hexagons
by which they are usually represented

called, since many have never been found in living tissue)
must have been discovered at the rate of hundreds a year
during the last sixty or seventy years, and they are not all
exhausted yet. It is these compounds which form the
basis of the thousands of medicines and drugs prescribed
by doctors and manufactured by great firms like 'Bor-
roughs & Wellcome' and 'Boots Pure Drug Co. Ltd.'
Then there are all the artificial dyes, including the so-
called aniline dyes, based largely on rings of carbon
atoms, and so on. All this brings us back to the point
from which we started that is, to the hundreds of labora-
tories attached to industrial firms all over Europe and
America. New discoveries are still being made, but the
way of the modern chemist has been made easier by his
great heritage.

CHAPTER XI

Magnetism and Electricity
i

IT may seem difficult for those who have grown up in this
'all-electric' age to realise that it is not so very long ago
that the electric light and the telephone were expensive
luxuries only to be found in the houses of the wealthy.
Electric trams (which are now being scrapped wholesale !)
only came into use during the first few years of this century,
and the electric trains much later still. The telegraph is of
longer standing; but, taken as a whole, electricity has
played its part in the everyday life of the people for little
more than half a century. Yet the very elementary
knowledge out of which all these marvellous inventions
have grown was held by that earliest of the Greek philo-
sophers, Thales, and probably by others before him.

We have already seen what that knowledge was. In
the earth there was to be found a hard blackish stone,
which had the peculiar property of attracting towards
itself bits of iron. Another substance, amber, behaved
in a rather similar way. When rubbed, it would then
pick up by 'attraction' anything which was very light.
That was really all that was definitely known. As there
was no obviously practical use to make of this knowledge,
the matter, as far as real investigations went, rested there.
There was, however, something savouring of the super-
natural in the curious behaviour of these two stones. It
is not therefore to be wondered at that many stories grew
up of their magical power, and of the wonders that could

no

MAGNETISM AND ELECTRICITY n

be performed by their aid; and later they became part
of the stock-in-trade of magicians, astrologers, and
alchemists of the Middle Ages. The Latin name for
the black stone which would attract iron was 'magnes,'
from which we get our modern word magnet. The name
was probably given because the stone was found in great
quantities in a district in Thessaly known as Magnesia.

The Mariners' Compass. Somewhere about the eleventh
century a really useful fact was discovered about this
Magnesian stone. If it were suspended, or floated in
something on water, it always came to rest in a definite
way with its long axis in a north and south direction. 1
Up till this time, directions on the earth had to be found
by the sun during the day, and by the stars at night.
The particular stars seen in the sky, as you know, vary
with the season of the year, some being seen only in
summer and some only in winter. There are, however,
some stars which are seen all the year round in the
northern hemisphere, and there is one star which always
keeps the same position relative to the earth. This is a
star to be found in the constellation of the Little Bear,
and is known as the Pole Star. The direction of the
Pole Star is geographical north.

The disadvantage of finding one's way about on the
sea by means of the stars is obvious, especially in these
northerly climates, where so often there simply are not
any stars to be seen. The result was that, during the
Middle Ages, ships rarely went very far from the coast.
The discovery of this property of the magnet of setting
in a north and south direction opened up great possi-
bilities in navigation, and by the time of Roger Bacon
(1214-1284) it was in fairly common use.

1 This was really a rediscovery ; it had been known centuries before.

ii2 THE ROAD TO MODERN SCIENCE

Roger Bacon in his book Opus Majus describes, in
some detail, the properties of the magnet, or the 'lode-
stone ' as it now began to be called ; * lode ' being the Anglo-
Saxon word for ' way.' He tells in particular of a compass
made by one Petrus Peregrinus or Peter the Pilgrim.
This was made by putting a magnet in a wooden cup
which was floated on a bowl of water. This cup always

Tof*

FIG. 13. Showing how Peter Peregrinus found the poles
of his spherical magnet

set so that the magnet inside it was in a north and south
direction. In one of the notebooks of Leonardo da
Vinci, that great artist-scientist about whom we have
already heard, there is a drawing of just such a magnet,
but with a compass card, showing eight points, mounted
over the bowl as an improvement.

Peter Peregrinus. It was the same Petrus Peregrinus
who discovered and named the ' poles ' of a magnet. He
first had a piece of lodestone rounded into a globe. He
then placed a needle on the globe and allowed it to 'set/
then he drew a line on the globe showing its direction.
He moved the needle to another place, and again marked

MAGNETISM AND ELECTRICITY 113

its direction. This he repeated until he had a number of
lines passing round the globe. Having done this, he
found that the lines all crossed one another at two points
on the globe which were at opposite ends of a diameter.
He realised that these lines were just like the meridians
(or lines of longitude) on the earth, which all pass through
the North and South Poles. He therefore gave the
name 'poles' to the two points on the lodestone where
his lines crossed.

Dr William Gilbert. During the two following
centuries, except for the improvement of compasses
and their increased use in navigation, the work of
Peregrinus was not followed up. In Queen Elizabeth's
reign, however, a great advance was made. A certain
Dr William Gilbert of Colchester, later Physician to the
Queen herself, became much interested in the lodestone
and began to investigate its peculiar properties really
scientifically.

He started off by rejecting all 'idle tales and trumpery'
of its magic properties. Then he repeated the work of
Peregrinus. He called the globe of lodestone a * Terrella,'
and pointed out that the 'poles' were definite points in
the stone where its power or virtue was concentrated.
He realised that these poles were of opposite nature to
each other, and called the one which set towards the north
the ' austral ' pole and the other the ' boreal ' pole. These
names he took from the Latin words ' Auster,' the south
wind, and 'Boreas,' the north wind. Nowadays they are
called the north-seeking and south-seeking poles or,
more simply but less correctly, the north and south poles
of the magnet.

In his next experiment he floated a magnet, whose
poles had been found, in a vessel on water. He then

8

n 4 THE ROAD TO MODERN SCIENCE

took in his hand another magnet, whose poles were also
known, and held its north-seeking pole towards the
south-seeking pole of the floating magnet. The latter
swung round towards the magnet in his hand, and
followed it however it was moved. When, however,
he held the south-seeking pole towards the south-seeking
pole of the floating magnet it 'put the other to flight.'
In this way he established the well-known law of attrac-
tion of unlike poles and repulsion of like poles, which is
the first thing nowadays to be learnt about magnets.

Next he took a long-shaped magnet, which he assured
himself had poles only at the ends, and broke it in half.
He found that the broken ends now were poles, each
being opposite in nature to the original one at the other
end of the broken half.

Terrestrial Magnetism. So much for the poles of the
magnet. Now, Gilbert asked himself, why does a
magnet always set itself in a north and south direction ?
The earlier answer to this question had been that the
magnet was attracted towards the stars in the constellation
of the Bear. Gilbert, however, from the first, thought
that the explanation was to be found in the earth
and not in the sky. He was a true scientist, however,
and knew that he must put his ideas to the test and
establish their truth by experiment. To do this he made
use of his terrella, that ball of natural lodestone. He
showed that a magnet on the surface of the terrella
behaved in exactly the same way as a magnet on the
surface of the earth that is, it set itself in a direction
pointing to the poles of the terrella. Therefore, he
argued, the earth and the terrella must be similar in their
natures. The earth must itself be a magnet.

The point on which he laid most stress was what he

MAGNETISM AND ELECTRICITY

115

called the ' magnetic dip.' He touched a needle with
a piece of lodestone and so made it into an artificial
magnet. This he suspended freely from its centre of
gravity just above the terrella. It not only set itself in
a north and south direction, but showed a definite dip
towards the pole of the terrella to which it was nearest.
Only if it were suspended midway between the two poles

Vo/e.

FIG. 14. Showing the 'dip' of a magnet freely suspended
above the surface of a terrella

did it take up a position parallel to the surface of the
latter (see fig. 14). Moreover, Gilbert found that a
magnet freely suspended above the surface of the earth
always dipped towards the North Pole so this further
emphasised the likeness between the earth and terrella.
He concluded, quite rightly as it was later shown, that
in the southern hemisphere the magnet would dip towards
the South Pole; while at the equator it should set in a
horizontal position. The angle between the dipping
magnet and a horizontal line through its mid-point is
:alled the * Angle of Dip/

ii6 THE ROAD TO MODERN SCIENCE

Magnetic Declination. Quite soon after the intro-
duction of the compass, navigators found that the needle
did not point exactly to the pole star and did not, there-
fore, give the true north. More awkward still, the angle
between the true north and the direction of the needle
varied considerably according to the position on the

FIG. 15. A simple dip needle

earth's surface. This angle is called the magnetic
declination. The compass was, therefore, not such an
accurate guide as had been hoped.

Although the declination varied so much, Gilbert
thought that the angle of dip would always be the same
at the same latitude and would always be zero at the
equator. He, accordingly, devised an instrument known
as the * Dip Needle/ which he hoped could be used by
navigators to tell the latitude. This consisted of a

MAGNETISM AND ELECTRICITY 117

magnetised needle, pivoted so that it could move in a
vertical plane, instead of a horizontal one as in the case
of a compass. When this vertical plane in which the
dip-needle can move is in the magnetic meridian, the
angle of dip can be read off on the circular scale (fig. 15).

Unfortunately it was found that the magnetic dip also
varied slightly at the same latitude, and so, after all,
Gilbert's dip-needle was not of much use to sailors.
Nowadays both the magnetic dip and the magnetic
declination have been determined at places all over the
world, and every ship is provided with records of these.
Maps have been drawn having lines on them joining up
all the places of the same magnetic declination. In this
way sailors are able to find their way accurately by the
compass.

This study of the magnetism of the earth is always
known as Terrestrial Magnetism.

Gilbert was also, naturally, interested in the property
exhibited by rubbed amber of attracting light objects to
itself. He discovered that amber was not the only
substance which had this power of attraction. Other
bodies such as glass and a number of gems behaved in a
similar way when rubbed with wool, silk, or hair. He
it was who first used the word Electricity' to describe
the strange effects produced in this way. He formed the
term from the Greek word for amber, electron.

Gilbert divided substances up into two classes electrics
which could be Electrified ' by rubbing, and non-electrics.
He found that electrified bodies lose their electricity if
held near a flame or otherwise heated; and also that it
was very difficult to electrify bodies on a damp day.

Gilbert laid sure foundations to the science of both

ii8 THE ROAD TO MODERN SCIENCE

magnetism and electricity. In fact, in magnetism, apart
from its connection with electricity, very little new has
been discovered since his day. Advance in that science
has been mainly along mathematical lines that is, in
discovering how to calculate exactly how big are the
forces of attraction which a magnet exerts. We shall
not attempt to deal with this part of the subject here.

II

During the seventeenth century little advance was made
in either Electricity or Magnetism, apart from the gradual
accumulation of knowledge concerning the magnetic
variations in different parts of the earth. During the
eighteenth century we find a great many people interested
in the study of electricity.

Two Kinds of Electricity. A Frenchman named
Dufay, after carrying out a number of experiments, con-
cluded that there were two kinds of electricity one pro-
duced when glass is rubbed, and the other when amber is
rubbed. He called the first 'vitreous* electricity and the
second 'resinous'; since vitrum is the Latin for glass
and amber is formed from the resin of certain pine trees.
He came to this conclusion by discovering that two
electrified bits of glass when suspended repelled each
other. So did two electrified bits of amber. But a piece
of electrified glass was attracted by a piece of electrified
amber. Here was a rule about electrified bodies similar
to that governing magnetic poles. It was quite easy after
that to classify other electrified bodies by seeing whether
they were attracted or repelled by an electrified rod of
glass.

Storing Electricity. We have already seen that Gilbert
found it very difficult to make his experiments work on a

MAGNETISM AND ELECTRICITY 119

damp day, because he could not produce the electricity
easily. A Dutch professor at Leyden conceived the idea
of storing electricity to get over this difficulty. He thought
that the electricity leaked away through the air; and to
prevent this leakage he tried to arrange to have the charged
body surrounded by a non-conductor that is, one of
Gilbert's electrics. This would hold the charge instead
of letting it pass through it. To do this he suspended a
bottle of water from a gun-barrel by means of a metal
wire passing through the cork into the water. The gun-
barrel was 'insulated' by suspending it by silk threads.
(Silk is a non-conductor or an electric.) Next he charged
the gun-barrel by an electrified glass body. Since the gun-
barrel was made of metal which is a conductor, he thought
that the charge would pass through into the water ; here it
would be protected by the surrounding glass flask which
was a non-conductor. Then an astonishing thing
occurred. He happened to touch the gun-barrel with one
hand and the glass bottle with the other. Thereupon he
got such a shock that he vowed he * would not take
another for the Kingdom of France.'

Other men, however, repeated the professor's experi-
ment and turned it to good account. A certain Abbe
Nollet amused the King of France by sending a 'shock'
through a line of guards holding hands. You may
imagine the effect ! Later, he repeated this experiment
with several hundred Carthusian Monks, who are said
to have given a sudden spring altogether when contact
was made. It was found that these shocks had no ill
effects. In fact, a little later electric shocks, within limits
of course, were actually prescribed by doctors for their
tonic effect.

The Leyden Jar. The original apparatus which had

120 THE ROAD TO MODERN SCIENCE

produced the first shock on the Dutch professor became
known as the ' Leyden jar/ Similar pieces of apparatus
are still made and called by this name. A brass knob
leading to the glass jar now replaces the gun-barrel, and
the glass bottle is coated inside and out with tinfoil. If a
metal wire is placed in contact with the outer tinfoil of a

o

1

JTin

FIG. 1 6. A modern form of Leyden jar

charged jar, and brought near to the brass knob, a bright
spark passes from the wire to the knob with a loud
crackle.

Electrical Machines. For a good many years after
Gilbert's time, electric charges were produced simply by
rubbing pieces of amber, glass, or sulphur on material,
such as the experimenter's coat or on his hand. During
the seventeenth century a means of obtaining larger
charges was devised. A ball of sulphur was mounted so
that it could be spun round on its axis, and the hand was
allowed to rub against the ball as it spun. In this way

PLATE XI

t;

o
CJ

I

5

rt

.3

a

<U

0>

a

a;
*C

CD

Cu

X

rt
*C

4->

w
IS

O

1-4

Q

PLATE XII

J ami 1 1 Fran kl in

Priestley's Electrical Machine

MAGNETISM AND ELECTRICITY 121

a charge was produce^ continuously by friction. This
earliest electric machine was improved in various ways,
the chief being to provide a driving wheel to turn the ball
of sulphur or glass which rubbed against a fixed leather
rubber. Both Priestley and Cavendish possessed electric
machines of this type (Plate XII). Later machines,
known as * influence ' machines, made use of the fact that
one body may be electrified by another even when there
is no contact. All modern electric machines are of this
type. The best known is the Wimshurst machine.

Benjamin Franklin (1706-1790). The greatest name of
the eighteenth century, as far as the science of electricity
is concerned, is that of Benjamin Franklin. He was an
American one of the very earliest of American scientists.
His father had left England in search of religious freedom
and settled in Boston, Massachusetts. Benjamin, after
helping his father for a while in his candle and soap store,
was apprenticed to a printer. Here he came into contact
with books. Not contented with printing them he began
to read them too, and began to acquire that wide know-
ledge and culture which was to make him stand out among
the men of his time.

After some years he left Boston and opened a shop of his
own in Philadelphia. His business thrived, and he began
to take an active part in public affairs ; on several occasions
he visited England, sometimes on Government business.
It was in this way that he met and became friendly with
the English chemist, Dr Joseph Priestley.

Although now perhaps best known for his scientific
achievements, his interest was not turned to electricity
until he was forty years old and already a prominent man
of his time in other ways. It was some experiments which
he saw performed with the Leyden jar which started him

122 THE ROAD TO MODERN SCIENCE

on this tack. Franklin's fame in the science of electricity
rests on two things : first, on a new theory he put forward
about the action of electricity; and secondly, on his
demonstration that lightning is really a huge electric
discharge or spark.

You will remember that Dufay had concluded from his
experiments that there were two different kinds of
electric fluid vitreous and resinous. Franklin suggested
that there was only one kind of fluid. Some bodies,
however, had a deficiency of this fluid and others a super-
fluity. Those with extra fluid might be called positively
charged, while those with less than the normal quantity
might be called negatively charged.

The similarity between a flash of lightning and the
sparks which can be drawn from an electrified body was
obvious, but the proof that the lightning and sparks were
identical in nature was not so easy. In 1752, however,
Franklin succeeded in showing that this really was the
case. He made a silk kite with a wood frame. To the
top of this he fastened a pointed iron rod. The kite was
fastened in the usual way to a length of twine at the end of
which hung a key. This in turn was fastened to a piece
of silk which Franklin held. His object was to charge the
kite from a thunder-cloud. The pointed iron rod was
used because it had been found out that points collected
electricity across air much better than flat surfaces. The
insulating silk attached to the key was, of course, to pre-
vent Franklin getting an electric shock.

The first day that there was a good thunder-storm
brewing Franklin and his son took the kite into a field
and flew it towards the thunder-cloud overhead. At
first nothing appeared to happen and the key remained
uncharged. The rain coming on, however, wetted the

MAGNETISM AND ELECTRICITY 123

kite. Then Franklin saw that the thread fibres of the
twine holding the kite were standing out in all direc-
tions, obviously electrified. He then put his knuckle to
the key and was able to draw off a spark, and also to charge
a Leyden jar from the key. In fact, the electricity taken
from the key would do everything that the electricity
taken from rubbed amber would do. It was clear that
a flash of lightning was an electric discharge either between
two charged clouds or between a cloud and the earth.

Franklin's work led directly to the invention of the
modern lightning conductor. This consists of a long rod
of metal ending with three points or forks projecting well
above the highest point of the building. Its lower end
is connected to a copper ribbon well buried in damp earth.
A discharge from a cloud to the earth will obviously take
the shortest path possible and will therefore strike the
highest parts of buildings. The materials of which most
buildings are made are very bad conductors of electricity,
and the discharge therefore meets with a great deal of
resistance, and much heat is developed. This causes
sudden expansion, which wrecks the building and very
often causes fire. A lightning conductor, however,
attracts the electricity to its points and conveys it easily
and quietly to the earth. It is most important that the
conductor should be well buried in the earth, otherwise
the foundation of the building will be wrecked.

Cavendish. \QM will recall that in the chapter ^on
Chemistry I said that in dealing with the early history of
nearly every branch of science we should come upon the
name of Cavendish. Well, here he is again, and once
more we find him measuring. This time it is something
rather more intangible than masses and volumes, for he is
measuring forces. So far, investigators had been content

124 THE ROAD TO MODERN SCIENCE

to distinguish between forces of attraction and forces oi
repulsion, and no attempt had been made to measure the
forces or the charges which produced them. The onl)
kind of force fully investigated at this time was the force
of gravity Newton had shown that this force varied
directly as the product of the attracting masses and in-
versely as the square of the distance between them,
Cavendish was able to show that an exactly similar lau
governed the attraction between charged bodies that is tc
say, the force either of attraction or of repulsion between
two charged bodies varies directly as the product of the
charges , and inversely as the square of the distance between
them.

Electrical Pressure or Potential. Nowadays we are all
very familiar with the term * voltage.' You probabl}
know that if there is a high voltage between two points 2
much greater current will flow than if there is only a lo\\
one. In a wireless set there is generally a high tension, 01
high voltage, battery and a low tension battery. These
terms are usually used where an electric current (that is 2
continuous flow of electricity) is concerned, but the)
apply just as much to the momentary passage of electricit)
in the form of a spark.

In the days of Cavendish no one had as yet been able tc
produce a continuous current of electricity. Cavendish
realised, however, that if two charged conductors were
joined, electricity would probably flow from one to the
other for a moment. He also realised that what decidec
which way the electricity would flow was not which bodj
held the greatest amount of electricity, but which had the
greatest * degree of electrification/ You will understand
what is meant by this if you think what determines which
way water flows. Look at the diagram. A and B are twc

MAGNETISM AND ELECTRICITY

125

vessels of water separated by a tap. There is obviously
more water in A than in B, but if the tap is opened

jf

Jf

FIG. 17. To illustrate pressure and capacity

water will flow from B to A. This is because the pressure
of water in B, as shown by the level to which it reaches, as
greater than in A. So water flows into A until the levels,

'*

+v /+

(a)

FIG. 1 8. (a) Equal charges. Electrical pressure greatest
on D. (b) Equal electrical pressure. Charge greatest on C

and therefore the pressures, are equal. Obviously, if the
same amount of water is put into both A and B, the water
in B will reach to a higher level or pressure than in A,
because the capacity of A is the greater. It is just the

126 THE ROAD TO MODERN SCIENCE

same with conductors holding electricity. If the same
amount of charge is given to two conductors C and D,
because C has the larger capacity for electricity, the degree
of electrification, or * electrical pressure/ will not be so
high as on D. If the two conductors are joined, electricity
will pass from D to C until the electrical pressures are
equal. Now, although the electrical pressures are equal,
C has more charge than D. Nowadays we talk of
electrical potential rather than electrical pressure. It
means exactly the same thing.

Electrical Capacity. The electrical capacity of a
conductor does not depend only on its size. In fact, it
does not really depend upon its size at all but on its extent
of surface, for the electricity of a charged body is to be
found only on its surface. Electrical capacity does not
depend on surface area alone, however ; other things can
alter the capacity. Suppose a conductor connected to the
earth is brought close up to another insulated conductor
which is charged. It is found that the electrical pressure,
or potential, of this charged conductor becomes less,
although no electricity has left it. To restore the potential
more charge must be added. Another way of putting
this is to say that the capacity of the charged conductor
has been increased by bringing up the earthed con-
ductor close, and more charge can be stored in it. If
the two conductors are separated by glass, wax, sulphur,
mica, or other insulator, instead of by air, the capacity is
still further increased. Such an arrangement is called a
condenser, which is an instrument used for storing
electricity. Franklin made the first condenser, but the
whole subject of potential and capacity was more fully
investigated by Cavendish.

Condensers. You are quite probably familiar with the

MAGNETISM AND ELECTRICITY 127

name condenser, as every wireless set contains one. A
condenser consists of an insulated conductor separated
by air, glass, or some other insulator from a conductor
connected to earth. If the insulated conductor is
charged, it will hold very much more electricity than
if the earthed conductor were not there. Cavendish's
condensers consisted of flat slabs of glass coated on
both sides with tinfoil. These were the two conductors.
The tinfoil on the lower side was, of course, the con-
ductor connected to earth; and the upper tinfoil was
the insulated one.

The Leyden jar is, of course, a condenser, as Cavendish
realised. In the modern form the inner and outer coat-
ings of the tinfoil on the glass bottle are the insulated
and earthed conductors. The charge given to the knob
is passed on by the chain to the inner coating.

Finally, Cavendish found that all so-called 'conductors '
did not allow electricity to pass through them with equal
ease. Moreover, he devised an experiment whereby he
could measure the relative conducting powers of different
materials. We have already seen that if a Leyden jar be
discharged by touching the knob with one hand and the
outside with the other, a powerful shock is experienced.
Instead of touching the knob directly with one hand,
Cavendish connected to it one end of a piece of the sub-
stance whose conductivity was to be investigated. He
then held the other end in one hand and discharged the
jar by touching the outside. In comparing conductivities
he adjusted the lengths of the material used until he
judged that the same degree of shock was experienced in
each case. The ratio of these lengths then gave the
relative conducting power of the materials.

In this way Cavendish found that ' Iron wire conducts

128 THE ROAD TO MODERN SCIENCE

four hundred million times better than rain or distilled
water, and sea- water conducts one hundred times better
than rain water. "

III

The Electric Current. The electrical machines and
condensers possessed by Cavendish and other experi-
menters were capable of providing quite a large store of
electricity and of giving a powerful spark when dis-
charged. The effect of the spark was, however, only
momentary. Apart from its use in some chemical experi-
ments already described, it was of little practical value,
although an endless source of entertainment. In 1780,
however, a discovery was made, the consequences of
which were to bring about the harnessing of electricity
to the practical requirements of modern civilisation.

Galvani (1737-1789). The discovery was made by an
Italian Professor of Anatomy, Luigi Galvani. He had
dissected a frog and left it pinned out on a table near to
an electrical machine. A student happened to touch
one of the inner nerves of the frog with the blade of his
scalpel (or dissecting knife). To his surprise he observed
that the frog's legs gave a sudden kick. Now the sudden
contraction of muscles when they receive an electric
shock was well known, and the kick of the frog's legs was
at once attributed to such an electrical cause. Galvani, at
first, naturally put the occurrence down to the presence
of the electrical machine. He determined, however, to in-
vestigate further. He prepared a number of frogs and
fixed them by means of brass hooks to an iron fence
in his garden. Knowing that lightning was an electric
discharge, he wished to see whether the same kick would
occur during a thunder-storm. Before any thunder-

MAGNETISM AND ELECTRICITY 129

storm occurred he made an important discovery while
he was putting up the frogs. In fixing the brass hooks
to the iron fence he found that, if the legs of the
frogs touched the iron fence, they gave a convulsive
twitch. This always happened whatever the state of
the weather. He then prepared more frogs, and fixed
them by means of brass hooks to an iron plate. He did
this indoors, so that any electrical disturbance outside
would not affect the result. On pressing the brass hook
against the iron plate the same kick was observed. Evi-
dently the cause of the kick was the contact of the two
different metals, brass and iron, with the frog's nerves
and muscles.

The explanation which Galvani gave of this unexpected
occurrence was that there was stored in the tissues of the
frog a quantity of electricity. This he called 'animal
electricity.' The contact of the metals with each other
and with the animal discharged this electricity, so causing
the muscles of the frog to contract suddenly.

Volta (1745-1827). There was another professor in
Italy who did not agree with this explanation given by
Galvani. He was Alessandro Volta, Professor of Natural
Philosophy in the University of Pavia. The explanation
he gave instead proved to be the right one and led to
further very fruitful results. Because of this, Galvani,
in spite of his careful investigations, lost a great deal of
credit for the important results which followed his
original discoveries.

Volta maintained that the electricity did not come from
the frog, but from the two different metals in contact.
The part played by the frog was simply to form a path.
He tried joining the two metals by other things, such as
blotting-paper soaked in brine, and found he could still

9

i 3 o THE ROAD TO MODERN SCIENCE

get a discharge of electricity. He got a much better
effect by using more than one pair of metals, and so made
his famous Volta's Pile, using zinc and copper as the two
metals.

Volta's Pile. The 'Pile' consisted of plates of zinc
separated from plates of copper by pieces of cardboard

soaked in dilute acid. The discs
were placed in the order, zinc
cardboard copper, zinc cardboard
copper, etc. In this way a zinc
plate was left free at one end,
and a copper plate at the other.
By bringing, a wire connected to
one end plate near to the other a
small spark could be drawn off.
The difference between this and
the Leyden jar was important.

_ . , In the latter, the spark was big,

FIG. 19. Arrangement of 11,1

elements in Volta's pile but once the spark had passed no

more electricity could be obtained

from the jar. With Volta's pile, on the other hand,
an indefinite number of small sparks could be drawn
off. In fact, a continuous source of electricity had been
produced. The quiet flow of this electricity along the
wire was henceforth called an electric current.

The Simple Cell. Volta's next step was to make what
is now known as a simple cell. Instead of using discs
of copper and zinc he took a strip of each metal and dipped
the strips into a cup of dilute acid. By joining up a
number of the cells by wires from the copper of one cell
to the zinc of the next he was able to obtain quite a strong
current. Such an arrangement of cells is called a battery.
The simple cell is never used as a practical source of

f f
Caraooara

MAGNETISM AND ELECTRICITY 131

current now, as there are certain grave disadvantages
attached to it. All the modern types of primary cells,
however, are really only elaborations of this original cell.
This does not apply to the well-known accumulator
which, of course, has first to be charged before it will
yield a current.

The Electric Current and Chemical Decomposition. We
have already seen what a tremendous help this invention
of Volta was to Davy in decomposing the caustic alkalis
and so finding a number of new elements. Davy's
successor at the Royal Institution, Michael Faraday,
investigated still further the action of an electric current
in decomposing chemical substances in solution. These
investigations of Faraday have had very far-reaching
results in two directions. In the first place, they helped
later chemists to explain the true nature of chemical
action. It is now known that in nearly all cases chemical
action between substances is due to the attraction of
opposite charges of electricity. In the second place,
these investigations laid the foundations of the very
important modern industry of electro-plating. That is
all we can say about that part of Faraday's work here.
There is a very great deal more to say about Faraday and
his work on electricity, but we must come back to him
again when we have dealt with the work of one or two
more of Davy's contemporaries.

Oersted (1777-1851). The first of these was a Dane,
Hans Christian Oersted. He is important, because it
was he who first was able to show the close connection
between magnetism and electricity. This discovery was
not an accident. It seemed to him extremely probable
that such a connection did exist, and he spent many years
trying to prove that it did. The successful experiment

i 3 2 THE ROAD TO MODERN SCIENCE

was really very simple. He held a wire carrying an
electric current over a pivoted magnetic needle, and
parallel to it. Immediately the magnet was deflected.
The direction of the current was then reversed in the
wire and the needle was then deflected in the opposite
direction. Other experiments had failed because hitherto
the needle had been placed at right angles to the wire
instead of parallel to it.

Andrt Marie Ampere. This discovery of Oersted was
immediately investigated further by a Frenchman named
Ampere. He brought mathematics to his aid, and was
able to measure the amount of force which caused the
needle to turn through a given angle. As this force was
due to the current flowing in the wire, this formed a
good way of measuring the strength of the current. The
ordinary units by which we measure a current to-day are
called amperes or 'amps' after this man. As a matter
of fact, a great many electrical terms are derived from the
names of great experimenters in electricity. An instru-
ment for detecting a current is called a galvanometer,
from Galvani ; or, if it is to measure the current in
amperes, it is called an ammeter. The earliest galvan-
ometer consisted of a coil of wire with a magnetic needle
pivoted or suspended at the centre of the coil. When a
current flowed through the wire the needle was deflected.

The Electric Telegraph. Ampere was the first man to
suggest the possibility of the electric telegraph. This
originally consisted of a galvanometer at the distant
receiving station, connected by two wires to a battery of
cells at the sending station. A current sent in one
direction deflected the needle of the galvanometer one way,
and a current in the other direction reversed the deflection.
A man named Morse invented his famous 'Morse Code.'

MAGNETISM AND ELECTRICITY 133

Taking a deflection in one direction to mean a dash and in
the other a dot, it was possible to transmit messages by
sending pulses of current along the wires to the galvan-
ometer. Later it was found that only one wire between
the stations was needed, as if the galvanometer and one
terminal of the battery were each connected to the ground,
the earth brought the current back.

Ohm (1789-1854). You will remember that Cavendish
first introduced the idea of potential, or electrical pressure
in connection with his condensers. The bigger the
difference of potential between the two plates of the con-
denser, the bigger the spark which can be got from them.
In the same way, the bigger the difference of potential
between the two terminals of a battery the greater is the
strength of the current which flows through the 'circuit'
connecting these terminals. A German contemporary of
Ampere and Oersted, named Georg Simon Ohm, showed
that the current produced was directly proportional to
the potential difference between the terminals, providing
that the path of the current was not altered. Ohm also
recognised that it was the constant potential difference
maintained between the terminals of the cell which was
the driving force of the current in the circuit. He called
the potential difference the Electromotive Force.

Ohm's Law. The actual current produced by any
constant electromotive force depends upon the path along
which it flows. The ratio of the electromotive force to
the current produced Ohm called the * Resistance ' of the
circuit. The bigger the resistance the less current is
produced. 'Ohm's Law y y as it is now called, is a very
important one, as it enables us to calculate just how much
current we shall get if we apply a known electromotive
force to a circuit of which we know the resistance, or, on

134 THE ROAD TO MODERN SCIENCE

the other hand, if we read the current flowing by means
of an ammeter, we can calculate the resistance of a circuit.
As the heating power of a current depends upon both the
current and the resistance it is very important to know
the value of both quantities.

Ohm's Law is usually written in the form :

Electromotive Force (E) ^ . /T ^

- - - ^ ' -Resistance (R),
Current (C)

IV

Michael Faraday (1791-1867). Having dealt with the
very important work of Oersted, Amp&re, and Ohm we can
now turn to that great scientist and great man, Michael
Faraday. In 1931 there was held in London's biggest
hall, the Albert Hall, a great electrical exhibition known
as the Faraday Exhibition. In the very centre of the hall
was a bust of Faraday and a stand bearing his original
notebooks. In a ring round this were set up the actual
apparatus used by Faraday in his original experiments,
many of which could actually be seen performed. Out
from this inner ring radiated in all directions, completely
filling the vast hall, models of the inventions and dis-
coveries of which one of his experiments had been the
starting-point. Perhaps the most striking thing of all
was to go from the outer ring where were shown the
intricate wonders of twentieth-century elaboration, back
to the centre and starting-point of it all ; to look on the
simple bits of apparatus and to read Faraday's simple and
clear explanation of the experiments which had had such
far-reaching results.

MAGNETISM AND ELECTRICITY 135

Who was Michael Faraday ? He was the son of a black-
smith, and at the age of thirteen was delivering papers
for a bookseller in London. Later he became apprenticed
to the bookseller and so came into close contact with the
world of books. From the first it was scientific books
which he devoured. He spent his meagre pocket-money
in making home-made apparatus to carry out for himself
the experiments about which he read. His first voltaic
pile was made from halfpennies and discs of zinc ! During
this time Davy was giving his lectures at the Royal
Institution. To some of these Faraday went. His
longing to devote himself entirely to science was increased
tenfold by these lectures. Finally he made up his mind
to a bold course of action. He had taken careful notes of
the lectures, and these he sent to Davy telling him of his
great desire and asking whether an opportunity could be
given him of realising it. Perhaps the most valuable
contribution that Davy made to science was his kindly
reception of this letter and his action in taking Faraday
into his laboratory as his assistant. So with two rooms
in the Royal Institution and a salary of twenty-five
shillings per week Faraday began his long and fruitful
career.

Not immediately did success and honours come.
There had been no preliminary college career for Faraday,
nor even a grammar-school education. He had to start
from the very beginning. At that time Sir Humphry
Davy's star filled the horizon of the scientific world, at
any rate in London, and Faraday was only a poor labora-
tory assistant when, in Faraday's first year at the Royal
Institution, Davy went on his famous European tour.
Faraday accompanied him as his assistant and valet.
The opportunity was a golden one, for in this way Faraday

136 THE ROAD TO MODERN SCIENCE

met personally almost all the famous scientists then work-
ing on the Continent.

On his return to England Faraday continued steadily
md thoroughly to lay those firm foundations on which
the great edifice of his later work was built. Unlike the
majority of scientists of his day, mathematics was of little
use to him. This was largely owing, of course, to lack
if training, but undoubtedly also to lack of aptitude. In
its place, however, he had what one might call a natural
intuition for selecting, out of a mass of facts, just those
ihat were important to the matter in hand. In short, he
ivas a scientific genius. Gradually this genius, in face of
:he many obstacles, won its way and placed Faraday at the
: orefront. At the Royal Institution, on Davy's retire-
nent, he stepped into the latter's place and became also
Director of the Laboratory. This position he held in
jpite of other offers until failing health made it necessary
or him to retire and end his days at Hampton Court;
>erhaps the most worthy of honour and gratitude of all
Britain's * state pensioners/ Both in England and abroad
he name of Michael Faraday was loved and honoured,
>ut he would accept no material tribute. He lived and
iied a poor man.

Faraday's appointment at the Royal Institution was a
chemical one in the first place, and his early work was all
m chemical lines. Valuable as it was it cannot here have
pecial mention. All this time, however, he was in daily
ouch with men working in every branch of science, and
le was fully aware of the problems with which they were
>ccupied. Faraday's active mind busied itself also with
hese problems, and it was in this way that he was led to
he study of electricity and to the discovery which gained
im such world-wide fame.

PLATE XIII

Michael Faraday

PLATE XIV

Faraday in his Laboratory at the Royal Institution

( Hy permission of the Royal Institution}

MAGNETISM AND ELECTRICITY 137

Electro-Magnetic Induction. Oersted's experiment had
shown that there was a very intimate connection between
magnetism and electricity. The following facts were now
established definitely:

(1) A magnet can induce or give rise to magnetism
in an adjacent iron body.

(2) An electric charge produced by friction on one
body can induce electricity in another body.

(3) An electric current gives rise to magnetism.

Certain questions presented themselves at once to
Faraday. Since an electric current gives rise to magnetic
effects, cannot magnetism give rise to a current ? Cannot
a current of electricity flowing in one wire induce a
current in a neighbouring wire ?

These were the questions which Faraday set himself to
answer ; and the experiments which finally gave him the
answers were all to be seen, just as he had them set up, at
the Faraday Exhibition in 1931. I am going to describe
the experiments to you as if they were successful straight
away, in order that you may understand them more easily.
Actually there were a good many experiments which were
not successful. Faraday did not make his great discovery
by luck, but by patient and careful research.

For the final successful experiment Faraday made a long
coil or helix of copper wire, the ends of which were con-
nected to a galvanometer which would register any current
produced in the wire. Into this he placed quickly the
whole length of a bar-magnet, and then pulled it out
again.

As the magnet moved into the coil of wire the needle
of the galvanometer moved, registering a current in the
coil of wire. While the magnet remained still in the coil

138 THE ROAD TO MODERN SCIENCE

no current was registered. When the magnet was pulled
out the galvanometer needle again moved, but in the
opposite direction, thus registering a reverse current in
the coil.

The net result of this experiment is that when a magnet
moves near a wire forming a closed circuit a current flows
in the wire. The direction of the current depends on
the direction in which the North Pole of the magnet

FIG. 20. Illustrating Faraday's experiment on induced currents

moves. If the magnet remains still near the circuit there
is no effect.

Next Faraday turned his attention to the second
question : Can one current induce another ? For this he
took a heavy iron ring. On one part he wound a great
many feet of copper wire (A) connecting the ends to a
galvanometer. On the opposite side he wound another
piece of wire (B) and connected the ends to a battery.
So long as a steady current flowed in B no movement
occurred in the galvanometer needle, showing that no
current had been induced in A. Just as the wire from B
was connected to the battery, however, there was a sudden
movement of the galvanometer needle joined to A. A
movement of the needle in the opposite direction occurred

MAGNETISM AND ELECTRICITY 139

when the B was disconnected from the battery. From
the experiment, therefore, Faraday concluded that a steady
current will not induce another current, but a momentary
* induced' current is formed on ' making ' or 'breaking'
the circuit.

Now let us see how Faraday explained these results.
The power possessed by magnets and electrified bodies

FIG. 21. Showing Faraday's 'Lines of Force'

of being able to attract * at a distance ' had always worried
scientists. The general explanation held during the
seventeenth and eighteenth centuries had been that some
subtle fluid issued from or entered the bodies and the
attracted bodies were caught up in this stream. Faraday
now put forward a new explanation of magnetic and
electric force which was such a fruitful one that it is now
universally adopted. It was a well-known fact in his
time that iron filings in the neighbourhood of a magnet
set themselves along definite curved lines stretching
from one pole of a magnet to the other. Faraday
suggested that the whole of the space surrounding a

i 4 o THE ROAD TO MODERN SCIENCE

magnet was in a state of strain, just as a piece of cloth
stretched tightly over a frame is strained. He said that
the forces producing this strain acted along definite
curved lines which he called lines of magnetic force.
These lines were shown very clearly by the iron filings
which were pulled into the direction of the force. Where
the magnetic force was very strong, the lines were crowded
together, as, for instance, near the North and South Poles.
Where the force was weaker fewer lines existed. He
showed that these lines tended to crowd into iron. If,
therefore, a piece of iron were placed near a magnet, there
would be a great number of magnetic lines of force passing
between the magnet and the piece of iron. Faraday
compared these lines to stretched elastic strings, always
trying to contract. If the piece of iron were free to move,
or very light, as in the case of iron filings, the lines would
contract and the iron would move towards the magnet.

Faraday used this new conception of the 'field of
force' surrounding a magnet to make one explanation
cover both of his experiments on induced currents.
Let us think first of the experiment in which he pushed
the bar-magnet into the coil of wire and then pulled it out
again. Try to imagine the magnet with its lines of
magnetic force filling all the space immediately round it.
Before the magnet was brought up to the coil none of the
lines of force threaded the latter. As it approached the
coil, however, more and more lines crowded in, until a
maximum was reached when the magnet was right inside.
When the magnet was pulled out the number of lines
diminished from this maximum until once again there
were none threading the coil. Now it was only when the
number of lines of force was changing that a current was
induced in the wire of the coil.

MAGNETISM AND ELECTRICITY 141

Now let us turn to the second experiment where the
coils A and B were wound on the iron ring, A being con-
nected to a galvanometer and B to a battery. Remember
that Oersted had shown that a magnetic field always is
present when an electric current flows. Faraday showed
that in this case the lines of force ran in a series of widen-
ing circles round the wire in which the current was

\
\

carri/iH.q

| f -. 1 ~.~^.-L- J *

I

FIG. 22. Showing lines of force round wire carrying current

flowing. When, therefore, a current flowed in the wire
B, circles of magnetic force would ' thread' the coil, and
the outer ones would also thread the coil A. When the
current was steady the number of lines of force threading
A would also be steady. But when B was first connected
to the battery both the current and its accompanying
lines of force had to grow from zero to their maximum
value. This happened very rapidly, but while it was
happening the galvanometer attached to A showed
that a current was induced in B. Similarly, when
the battery was disconnected from B, both the current
and the magnetic field diminished suddenly to zero.

i 4 2 THE ROAD TO MODERN SCIENCE

During the change another induced current flowed.
Both experiments, then, really gave the same result.
Whenever the lines of magnetic force cutting a wire
which is part of a closed circuit are changing, a current
is induced in the wire. If the lines are increasing, the
current is in one direction; if they are decreasing then
the current is reversed. It is immaterial, of course, how
the changing magnetic field is produced. It may be
either by a magnet or by another current.

'7l> Outside Ci

FIG. 23. Diagram to show principle of the dynamo

The Dynamo. It was not long before the practical
results of this discovery were realised and put to use in
the invention of the dynamo and the electric motor.
With these inventions was ushered in the * Electric Age '
in which we live. Briefly the dynamo is a device to
keep coils of wire continually cutting lines of magnetic
force. In this way a perpetual induced current is
formed in the coil and led off and used in any way
which may be desired. In its simplest form a coil of
wire is revolved between the poles of a large horse-shoe
magnet, so that the coil is alternately at right angles to,
and parallel to, the lines of force passing between the

MAGNETISM AND ELECTRICITY 143

poles of the magnet. This means that the number of
lines 'threading' the coil is a maximum when the coil
is at right angles and a minimum when parallel to the
lines of force. In this way the direction of the current
is continually reversed and what is known as an 'alter-
nating current ' is formed. Formerly a device to change
this to a ' direct ' current was employed, but this has now
been found to be unnecessary and is not so much used.

You may wonder why the dynamo is better than a
battery for producing an electric current. The answer
is that one dynamo can do the work of a very great number
of cells. Such a battery of cells is unwieldy and expensive.
The materials also are constantly being used up. Once
a dynamo is made, apart from a certain amount of wear
and tear, it is more or less permanent. The chief
expense is in the source of energy to turn the coil. The
best and cheapest source is water-power, and that is why
mountainous countries such as Scandinavia and Switzer-
land have such splendid electric services. Other countries
use chiefly steam-power, with coal or oil as fuel.

The Electric Motor. The electric motor is similar to
the dynamo in construction. Instead, however, of the
coil being turned between the poles of the magnet to
produce the current, a current is sent through the coil.
The attraction between the poles of the magnet and the
magnetic field due to the current then makes the coil
rotate; and if the necessary gear is attached to the coil
it can be made to do work. It cannot be expected that
the working of an electric motor can be fully understood
from this description, but an explanation can be found in
any text-book on electricity.

It is quite impossible to enumerate the many inventions
which followed on Faraday's discovery. The telephone

144 THE ROAD TO MODERN SCIENCE

is just one example. During- the rest of the nineteenth
century one invention followed another.

James Clerk Maxwell (1831-1879). Just one more
name we must mention is that of James Clerk Maxwell,
for, in a way, he may be said to have rounded off Fara-
day's work. Faraday, we have seen, was no mathe-
matician. The proofs he brought in support of his
theories were experimental proofs and were never sup-
ported by mathematics. Now a scientist dearly loves
mathematical proofs, and indeed they are very useful, not
only as confirmation of experiment but in predicting new
experimental results.

Maxwell was a very gifted Professor of Mathematics.
He was a younger man than Faraday, being only thirty-
six when Faraday died an old man of seventy-six. He
was lucky enough to know Faraday personally, however,
and was especially interested in the latter's idea of lines
of force. His great work was to show mathematically
that Faraday was right in this idea. He then went on
to show, all by his mathematical calculations, that light,
plain common-or-garden light, was what he termed an
* electro-magnetic ' phenomenon. What he meant by
that was that the particular disturbance in the ether
which, when it hits our eyes, enables us to 'see,' really
consists of a succession of pulses of a force which is of
the same kind as the force causing the strain which we
call a magnetic field. That is all very well, it may be said,
if one happens to be interested in that kind of thing, but
it really does not mean much to anyone who is not a
mathematician. That is quite true; but by those same
abstruse mathematical calculations, Maxwell predicted
the formation of 'wireless waves.' This set a man named
Hertz looking for them ; and he found them ! It must be

MAGNETISM AND ELECTRICITY 145

admitted the finding of wireless waves is of considerable
interest to a great many people. But we will talk of these
again later.

Maxwell died in 1879, more than fifty years ago.
Needless to say, discoveries concerning electricity have
occurred since then. They are, however, of quite a
different nature from those dealt with in this chapter,
and link up more closely with present-day work which
is still going on. We will, therefore, leave them till the
last chapter of all.

10

CHAPTER XII

The Development of Power

i

Power in the Ancient World. The pyramids of Egypt,
built some four thousand years ago, are monuments of
engineering skill, and call forth the admiration of all who
gaze upon them. The power used to raise those huge
masses of stone to the top of the pyramid a tremendous
height must have been enormous. Yet it was all human
power, and as far as we know, unaided by any mechanical
device, with the possible exception of the lever. Armies
of slaves, harnessed by ropes to the stone blocks, used
their concerted efforts to move them ; and the time taken
to hew out one block and bring it to its final position in
the building must have been very considerable.

There is no need to remind you of the state of things
to-day. Mechanical power is everywhere used for
moving, transporting, and lifting materials of all kinds.
The actual muscular power of humans or animals is used
less and less, and there are few operations for which no
machine has ever been devised. The story of how this
change came about is the subject of this chapter.

Force. We must first be quite clear what we mean by
a machine. The dictionary defines a machine as 'an
instrument of force/ which brings in another word to
be clearly understood. The idea behind the expression
to 'use physical force' will make a very good starting-
place.

Now, if you use force on something, unless you are

146

THE DEVELOPMENT OF POWER 147

resisted, motion of some kind will follow, either of you
yourself or of the object on which force is exerted, or
very probably of both. Suppose now you want to lift a
heavy sack two or three feet. The sack is heavy because
there is a very strong force (of gravity) pulling it towards
the centre of the earth. To lift that sack you must exert
on it a force which is greater than the force of gravity.
If you are not very strong you may not have sufficient
force at your command to do this. There are various
ways, however, in which you could contrive to make such
as you have enough.

Machines. For instance, you might use one or more
pulleys. A pulley is a small grooved wheel which turns
very smoothly on its axle. It is generally fixed in a frame
which can be fastened to the ceiling or to some support.
Suppose, now, you fasten a rope to the sack, pass the rope
over the pulley, and then pull the rope. You might now
be able to lift the sack. You would, as a matter of fact,
have to exert just as much force as the weight of the sack,
but you could now use the weight of your body to help
you. If you had two pulleys, arranged as shown, you
need only use half the force ; or with six, only one-sixth
of the force. A set of pulleys, therefore, is a machine
which allows you to overcome one force by using a
smaller one.

The lever is another device of the same sort. Suppose
a tin, such as a treacle tin, has its lid jammed in firmly,
so that you cannot get it open by pulling with your fingers.
If a spanner, or a knife, is put under the rim of the lid
and the other end pressed down, it is possible to 'lever,' or
prise, it open. The simplest kind of lever is a straight rod
which can hinge about some definite point called the
fulcrum. In the case above, the spanner hinged on the

148

THE ROAD TO MODERN SCIENCE

edge of the tin as the fulcrum. You probably know quite
well that the longer the spanner you use the less force
will you have to exert on the end. There are many
different kinds of levers. A see-saw, or a weighing

FIG. 24. Showing various arrangements of pulleys to reduce
the force needed to lift a weight

machine, are simple types where the fulcrum is in the
middle. There are many other more complicated kinds,
but the same rule applies to them all. If the force is
exerted at a point which is farther away from the fulcrum
than is the load, then a smaller force is needed to lift or
move the latter. The greater the distance of the force
from the fulcrum, compared with the distance of the load
from the fulcrum, the smaller the force needed.

THE DEVELOPMENT OF POWER 149

Archimedes (287-212 B.C.). It was Archimedes who
first used pulleys and levers as mechanical aids to human
force. He used these devices in helping the men of
Syracuse to move their ships and tackle; and we have
seen, in Part I, how he used many mechanical aids in the
defence of the town against the Romans.

Leonardo da Vinci. After Archimedes, the next man
we hear of as interesting himself in these devices was
Leonardo da Vinci. In the story of his life we read that
he constructed a machine to raise the Holy Nail, which
was a prized possession of Milan, to its position above
the altar of the great cathedral which was being built.
His notebooks are full of plans for similar devices.

The next advance was to find a machine which would
act as a substitute for human power. This accomplished,
pulleys and levers would still be used as aids to the new
force. Before coming directly to these new machines,
there is a long story to tell of discoveries which led ulti-
mately to their invention, although in so doing we may
seem to wander rather far afield.

The Suction Pump. The Duke of Tuscany to whom
Galileo was appointed mathematician and philosopher
after he had left Padua wished to have a new well
made. Accordingly the well was dug, and it had to be
a deep one, forty feet down to the water. The next
thing was to fit a pump to bring the water to the surface
of the earth. Now pumps were known and used in the
time of Aristotle. The pump in use at this time con-
sisted of a long tube, the length of the well, dipping into
the water at the bottom. At the top it opened into a
wider cylinder (C) by means of a little door or valve (B)
which would only open upwards. Fitting into the
cylinder was a disc or piston (P) which could just move

THE ROAD TO MODERN SCIENCE

up and down* when worked by a rod. In the piston was
another valve (A) which also would only open upwards.

To work the pump, the piston was moved first down
then up, and the movement repeated until an upward
movement brought up water on top of the
piston. Let us see how this came about.
The downward stroke of the piston would
squeeze out the air beneath it in the cylinder.
On pulling up the piston, therefore, an
empty space or vacuum would tend to be
formed; but instead of this happening, the
air from the pipe was sucked up into the
cylinder through the valve (B), while some
water was sucked into the pipe. The next
downward stroke of the piston squeezed out
this new lot of air, and on the upward stroke
still more water was sucked up. Finally,
water was sucked into the cylinder. On
the following downward stroke it was the
water which was squeezed through the
valve (A), which then closed under the
weight of the water so that on the upward
stroke the water was carried up with the
A suction piston and came out of the mouth of the
P ump pump.

The Greek philosophers had been almost unanimous
in thinking that a vacuum an entirely empty space
could not exist. Whenever it seemed likely that one
might be formed, something would always move in to
fill up the space. This conclusion of theirs was generally
expressed by the phrase 'Nature abhors a vacuum.' In
the case of the pump, when the piston is raised after
squeezing all the air out from under it, there would

FIG. 25.

THE DEVELOPMENT OF POWER 151

obviously seem to be a possibility of the formation of a
vacuum. Instead, however, the water and the air from
the pipe push up through (B), and take the place of air
squeezed out, * because/ as the old philosophers said,
* Nature abhors a vacuum/

Now when the pump over the Duke of Tuscany's well
was set to work a quite unprecedented thing occurred.
No water could be raised to the surface. The water
refused to rise higher than thirty-four feet. (The well,
you remember, was forty feet deep.) Nothing the men
could do would get it beyond this height. Galileo was
called in to see if he could offer any suggestion, but even
he could not see the reason for the failure of the pump.
All he could say was that evidently Nature's abhorrence
of a vacuum did not extend beyond thirty-four feet!
This problem of the pump was one which Galileo himself
never solved.

Evangelista Torricelli (1608-1647). The man who did
find the solution, however, was one of his pupils, Evangel-
ista Torricelli. He pondered over it for a long time and
finally arrived at what he thought was the true explana-
tion. To test his theory he devised an experiment in
which he determined to use mercury instead of water.
Mercury is much heavier than water, and so occupies less
space, weight for weight. He needed for his experiment
very thick glass tubes, and these took a long time to make.
The tubes were about a yard long and closed at one end.
He filled the tube with mercury, and then closed the open
end with his thumb and inverted the tube into a basin of
mercury. The mercury began to run out of the tube,
but when the column of liquid was thirty inches high no
more ran out and it remained quite steady.

This was what Torricelli had expected to happen. He

15*

THE ROAD TO MODERN SCIENCE

said that the space above the top of the mercury in the.
tube was a vacuum. The column of mercury was held
up in the tube by the pressure of the air outside pressing
on the surface of the mercury in the basin. He calculated

that a column of mercury thirty
inches high weighed the same as
a column of water (of the same
thickness) which was thirty-four
feet high. The pump failed to
work because the air could not
hold up a column of water longer
than thirty-four feet.

A great many people laughed
this explanation to scorn. If the
pressure of the atmosphere were
the same as that of a column of
mercury thirty inches high, that
meant that the air was pressing
down on us with a weight of
fifteen pounds on every square
inch. This, they said, was absurd, because such a
pressure would crush us. We now know, of course,
that the blood and air in our bodies is pressing outwards
with an equal pressure. The result is that we are not
conscious of the pressure of the atmosphere unless it
alters in some way and becomes either less or more than
the pressure inside our bodies.

Blaise Pascal (1623-1662). Torricelli wrote about his
experiment to some friends in Paris, and, in this way, a
certain very clever Frenchman named Blaise Pascal, who
lived at Rouen, came to hear about it. He was very much
interested and thought that Torricelli was probably right
in his explanation; but before the matter was quite

FIG. 26. Torricelli 's
experiment

PLATE XV

CO

8

*C

CO

a;
W>

W)

k I
^

*J

4-*

I

w

fe

CO

a

PLATE XVI

Cfl

C/3

a

o.

I

i

^ 0,
G c^

11

w '

o

^ w

g

D

O

THE DEVELOPMENT OF POWER 153

settled he felt that it should be tested further. He
reasoned that if the column of mercury in the tube were
really held up by the pressure of the atmosphere, then,
if the latter altered in any way, the height of the mercury
column should alter correspondingly. The only way
which he cduld think of to alter the pressure of the atmo-
sphere was to perform the experiment higher up above
the earth's surface. Since there was then less air above
to press down on the mercury, the pressure would be less.
If Torricelli's explanation was correct the column of
mercury held up would be shorter.

The only high place near Rouen was the top of the
Cathedral tower. So Pascal, when he had got the
necessary thick glass tubes, repeated Torricelli's experi-
ment at the foot of the tower and then again at the top.
The mercury column was certainly a little shorter, but
not enough to satisfy Pascal. He determined that the
experiment must be repeated at some place where a
greater difference in level could be achieved. The
obvious solution was at the foot and at the top of a
mountain. Unfortunately there were no mountains near
Rouen. Pascal was not at all strong and could not under-
take the necessary journey, for travelling in those days was
a very arduous matter. However, he had a brother-in-
law named Perrier, who lived in the mountainous district
of Auvergne. Pascal, therefore, wrote to Perrier describ-
ing his experiment and asking if he would undertake to
repeat it at the foot and the top of one of the high
mountains.

Perrier gladly consented, and prepared two tubes of
mercury which he inverted in two separate bowls. One
of these he set up at the foot of the mountain and left two
men in charge to note any changes which might occur;

154 THE ROAD TO MODERN SCIENCE

and then with a companion he set off with the second tube
to the top of the mountain. Sure enough, when they
reached the top the mercury column was about three
inches shorter than it had been at the bottom. As they
came down again they found that the mercury gradually
rose in the tube until at the foot of the mountain it was
once more the same height as that in the tube which had
been left there.

The news of this successful experiment pleased Pascal
very much indeed, and it was now quite certain that
Torricelli's explanation was the right one. The latter 's
inverted tubes of mercury, moreover, furnished a very con-
venient way of measuring the pressure of the atmosphere
from day to day, for it was found that this was not quite
constant. Such was, in fact, the beginning of the instru-
ment known as the Barometer, which has proved so useful
to us in our knowledge of weather conditions. In its
more modern form the aneroid barometer, which does not
contain any mercury it is used in aeroplanes to measure
the height above the surface of the earth, for it is known
that the pressure of the atmosphere decreases regularly
with the height above sea-level.

Otto von Guericke (1602-1686). At that time news
travelled very slowly indeed, so that it happened that on
the other side of the Alps from Italy another man was
finding out about the tremendous pressure exerted by the
atmosphere, in complete ignorance of the experiments of
Torricelli and Pascal. This man was Otto von Guericke,
a Burgomaster of Magdeburg in Saxony. He had been
educated at various centres of learning, and, before his
election as Burgomaster, had been chief engineer to the
town of Erfurt.

Guericke was drawn to the subject in quite a different

THE DEVELOPMENT OF POWER 155

manner from Torricelli. His first interest was in
Astronomy. At that time it was still a debated question as
to whether the space between the sun and the planets and
stars was completely empty or filled with air. Guericke
took the former view, for, said he, if the planets move
through air, then they will encounter friction and gradu-
ally slow down. This, you must remember, was in the
days of Kepler, and before the days of Newton, and the
movement of the planets was a burning topic. Guericke
maintained that the only way to study the motion of the
planets was to produce a vacuum and so obtain con-
ditions which were comparable to those of the Heavens.

He had, of course, been brought up in the traditional
doctrine that Nature abhors a vacuum. In him, however,
was the spirit of Galileo and the new age, and he de-
termined to try for himself and see if he could obtain one.
His first attempt consisted in trying to pump the water
out of a wooden cask with a suction-pump of the kind we
have described, without allowing any air to enter. He
found the pump very hard to work, and before long there
was a loud hissing as the air from outside forced its way
in through the joints. He tried again with two casks,
one inside the other; but although he managed to
pump all the water out, he found that air had taken its
place.

He persevered, however, and next used a copper globe
filled with water and attached his pump as before. This
time the pumping was so hard that it took two men to
work the pump, using all their strength. Then, just as
they seemed to be getting on, the globe collapsed with
a tremendous report, alarming everybody very much.
However, this attempt was obviously more successful
than the last, so Guericke had a still stronger globe made

156 THE ROAD TO MODERN SCIENCE

and a better pump and tried again. This time he
succeeded and obtained a nearly complete vacuum.
The globe was fitted with a stop-cock, or tap, which was
turned off when the water had been pumped out. When
the stop-cock was opened the air rushed in with such
violence that it was very dangerous to stand near.
Guericke writes that, even at a considerable distance,
one's breath was taken away as the air rushed in.

His next idea was to try to pump out the air from the
globe straight away, instead of displacing it by water first.
He had to alter his pump a little to do this, but soon
succeeded. With this new air-pump he was able to
obtain a vacuum fairly easily, and soon devised some very
striking experiments to show the enormous pressure
exerted by the air on the outside of an evacuated vessel.
These aroused great interest and amazement in the people
who saw them, and soon the fame of Guericke reached
the Emperor's ears. He at once desired to see these
things for himself, and accordingly Guericke arranged
two very spectacular experiments which he performed
before the Emperor Ferdinand III and his Court.

The first experiment has become very famous and is
always known as the Magdeburg Hemispheres experi-
ment. A large sphere of about fifteen inches diameter
was divided into halves which fitted tightly together with
a leather ring in between to make the joint airtight. To
a nozzle in one hemisphere the air-pump was fitted, and
the air was then pumped from out the globe. It was then
shown that, although formerly the halves had separated
easily enough, after the globe had been exhausted, they
were now held firmly together. Horses were then
harnessed to hooks on the globe, eight to either side.
Straining with all their might, they were just able to

THE DEVELOPMENT OF POWER 157

separate the halves, which fell apart with a loud report
(Plate XV).

The second experiment was, perhaps, even more
striking. A similar globe, only this time not divided in
half, was again evacuated and the nozzle connected to the
bottom of a cylinder. This contained a heavy piston
fitting the cylinder tightly. Attached to the piston was
a rope passing over a pulley and dividing into twenty
smaller ropes. Each of these was held by a man standing
on the ground. The men had to exert all their strength
to keep the heavy piston in position. The tap of the globe
was then opened. Immediately the air from underneath
the piston rushed into the empty globe, causing such a
difference of pressure between each side of the piston that
the latter was pushed down violently and with such force
that the men holding the ropes were jerked violently off
their feet (Plate XVI).

So, in quite another way, Guericke showed that every-
where the atmosphere was exerting this enormous
pressure. As a rule it was resisted by an equal and
opposite pressure and so was apparently ineffective. If,
however, this resistance was removed, a tremendous force
was immediately available. It was this force which was
to be used in the inventions of the new machines.

II

The Steam-Engine

Dionysius Papin (1647-1712). It is to a Frenchman
named Papin that the origination of the idea of these new
engines is usually ascribed, although he himself was
never very successful in getting them to work. Inventors
generally have to depend upon other workmen for the

158 THE ROAD TO MODERN SCIENCE

making of their models, and bad workmanship may often
bring failure when the idea on which the invention is
constructed is a perfectly sound one. This was, to a
certain extent, the case with Papin's invention; but he
was also handicapped by the fact that he had no money of
his own and had to depend for the carrying out of his
plans on his patron, the Landgrave of Hessen in Germany.

Papin was a French Protestant, and all Protestants were
expelled from France in 1685. With many of his fellow-
countrymen Papin went to Germany and obtained an
appointment at the University of Marburg under the
patronage of the Landgrave of Hessen. At this time
there was constant warfare with Louis XIV of France,
and, although the Landgrave was interested in Papin's
invention, he was continually being distracted by other
claims on his attention. Consequently Papin was never
able to construct a really successful engine, and after a
time the Landgrave lost interest. Meanwhile, however,
Papin had been in communication with certain members
of the English Royal Society. Earlier in his life he had
spent some years in England and had known Boyle and
his assistant, Hooke, who also had been working on the
subject of atmospheric pressure. Hooke had given
Papin's plans to a very clever iron-worker, named New-
comen, and the latter had soon constructed a good work-
ing engine from these plans. This engine is usually
known as Newcomen's engine, but we must remember
that the invention really came from the Frenchman,
Papin.

Newcomen's Engine (1711). The engine was originally
designed to work a pump to pump the water out of mines
and prevent them from flooding.

The piston-rod of the suction-pump was attached to a

THE DEVELOPMENT OF POWER

weight (W) connected to one end of a lever (L). The
other end of the lever was connected to a piston which
could move up and down in the cylinder (C). The
piston was normally kept at the top of the cylinder by
the weight (W). Steam was then passed into the cylinder

FIG. 27. Diagram to show the principle of Newcomen's engine

underneath the piston, from the boiler (B), and then the
steam was condensed by a dose of cold water from another
jet. Now, when steam is condensed to water, the volume
becomes sixteen hundred times smaller. The condensa-
tion of the steam, therefore, practically caused a vacuum
under the piston, so that the latter was immediately
pushed down by the pressure of the atmosphere to the
bottom of the cylinder. This worked the lever, so causing
an upward stroke of the suction-pump. The steam from

160 THE ROAD TO MODERN SCIENCE

the boiler was then turned on again so that steam entered
the cylinder and the weight pulled the piston up again.
This caused the downstroke of the suction-pump. Thus
the only attention the engine needed was the alternate
turning on and off of the taps controlling the steam and
water jets. There is a story that a lazy boy was put to do
this who soon tired of his monotonous job. Being some-
what of an inventor he contrived to tie strings from the
taps to the ends of the lever so that the engine itself did
the job. Once started, the engine was now self-working.
Considerable doubt has been thrown on the truth of this
story, but it serves well to show the principle of automatic
working.

James Watt (1736-1819). Newcomen's engines were
used in the larger mines for more than fifty years, but
they were very expensive, because a tremendous amount
of coal was used in producing the steam. The man who
made the steam-engine a really practical proposition, and
whose name is the most famous in this connection, was
James Watt of Glasgow. He was born in Greenock in
1736, and, as a youth, was apprenticed as a mechanic first
in Glasgow and then in London. In 1757 he obtained
a post at Glasgow University, where his work was to look
after the instruments and models used in the science
department. Here he met and became friendly with
Joseph Black, who was afterwards to become so famous
in the scientific world.

It was while Watt was at the university that a model of
one of Newcomen's engines came under his hand for
repair. He at once saw its disadvantages and set about
trying to find a way to overcome them. He realised that
the reason why so much coal was used was because a
great deal of the steam which entered the cylinder at

THE DEVELOPMENT OF POWER

161

once condensed and gave up its heat to the cold cylinder.
Only when the cylinder was as hot as the steam did it
begin to fill up with the latter. What was wanted was
to find a way of condensing the steam when the cylinder
was full, without again cooling the cylinder.

It was not long before he saw how this could be done.
If, instead of sending into the cylinder a jet of water, a

I

FIG. 28. Showing how Watt's condenser was fitted
to Newcomers engine

tap was opened connecting the cylinder with a vessel
empty of air and kept permanently cold, the steam would
rush into this vessel and condense there without cooling
the cylinder. This vessel is known as the condenser
(see fig. 28).

Watt's difficulty was the same as Papin's, namely, to
find the money to get a model made, for he had none
himself. At first the owner of the famous Carron Iron
Works in Scotland helped him, for he hoped to use the
engine in his mines. Unfortunately his workmen made
the engine very badly, and it would not work, so Watt
had to give it up for the time being. Some years later,

ii

1 62 THE ROAD TO MODERN SCIENCE

however, he found another man ready to help him. This
man was Matthew Boulton, who owned a large factory
near Birmingham, where he made all sorts of iron goods.
His men made a much better job of the model, which,
this time, was entirely successful. The fame of the engine
soon spread, and, before long, Watt's engines were being
used for all sorts of purposes besides pumping mines.

FIG. 29. Diagram of high pressure steam-engine

When valve is in position V l stearn enters by S t and drives piston to right. This auto-
matically moves valve to position V., closing Sj and opening S,. The piston is now driven
to left and steam on left side is driven to condenser through outlet C. In this way
steam enters alternately first one side and then the other, driving the piston backwards
and forwards.

These, of course, could now be pumped dry more success-
fully, and so coal became more plentiful and cheaper.
Mills and factories hitherto worked by water-power now
changed over to the new steam-engine, and the Industrial
Revolution had begun.

As skill in the working of iron increased, boilers were
constructed which could stand a much greater pressure
of steam. Instead of working the engine by the pressure
of the atmosphere, * high pressure ' engines are now used
where steam is forced into the cylinder under pressure,
first one side of the piston and then the other, and led away

THE DEVELOPMENT OF POWER 163

to the condenser through automatically operating valves.
The diagram shows this.

Steam-engines are still greatly used to-day where coal
is plentiful, although in many countries with cheap water-
power they are almost everywhere replaced by the electric-
motor. Their chief use is, of course, in the steam
locomotive which draws the majority of our trains.

Ill

The Internal Combustion Engine

The nineteenth century was the great age of steam-
power. In the latter half, however, another kind of
engine was invented which to-day bids fair to outrival
the older steam-engine. This was the internal com-
bustion engine. In each case the source of the energy
which drives the engine is the chemical energy liberated
as heat in the combustion of a fuel. In the steam-engine
the combustion of the coal or oil (which is used in many
ships) takes place outside the engine. In the internal
combustion engine the fuel is fired in the cylinder of the
engine itself. In this case, of course, the fuel is not coal.
Originally it was a mixture of coal-gas and air. Coal-gas
is obtained by heating coal very strongly out of contact
with air, so that it does not burn. Nowadays a mixture of
the vapour of petrol or of a heavier oil and air is most
generally used as fuel, although a mixture of gas and air
is still employed.

The engine consists of a piston and cylinder, as before.
When the piston is near the top of the cylinder the vapour
and air mixture is fired by an electric spark generated by
the magnet. The hot gases formed expand and push
down the piston. The piston is connected to a crank-

164 THE ROAD TO MODERN SCIENCE

shaft which it turns as it descends. To the shaft is fixed
a heavy flywheel, which, once started, goes on revolving

cfosecL fn/tfrtfa

FIG. 30. Showing the four strokes of a petrol-engine. The valves
are worked automatically from the revolving crankshaft

under its own momentum and so pushes up the piston,
driving out the burnt gases the exhaust through
an opening. At this point the crankshaft will prob-
ably receive an impulse from the firing of petrol vapour

THE DEVELOPMENT OF POWER 165

in another cylinder, and so the piston in the first one
is pulled down once more, sucking in above it a fresh
supply of petrol vapour. On the upward stroke this is
compressed and is fired just as the piston reaches the
top of its stroke, starting the whole cycle again. Nowa-
days there are usually four or six or even more cylinders
to an engine, so that the crankshaft gets a succession of
impulses during one revolution. In almost all motor-cars
each cylinder is fired every fourth stroke of its piston,
giving an impulse to the crankshaft. The other three
strokes are produced by the revolution of the crankshaft.

(1) The piston is driven downwards by the ex-
pansion of the hot gases produced by firing the petrol
vapour.

(2) The upstroke drives out these gases through the
exhaust.

(3) The following downstroke sucks in fresh petrol
vapour.

(4) The upstroke compresses this petrol vapour
which is fired by an electric spark just before the next
downstroke should begin. The timing of this firing
is very important, as every motorist knows.

In motor-cycles a * two-stroke' engine is sometimes
fitted.

The first successful petrol-engine was made by a I
German, Gottlieb Daimler. He fitted one of his engines
to a bicycle, and later used one in a boat on the River
Seine. A French firm then began manufacturing
carriages carrying a petrol-engine, and so the motor-car
originated. In England, an attempt had already been
made to do the same thing with the steam-engine, but
the 'steam-car' had proved a very cumbersome affair.

166 THE ROAD TO MODERN SCIENCE

At the beginning of the present century motor-cars were
improved out of all knowledge, and not long ago it seemed
as if motor transport might supersede steam-trains alto-
gether. There is, however, still much to be said for the
latter, and, although it is not safe to prophesy anything
nowadays, steam-trains will probably remain with us
for a while yet, at any rate until electric power in this
country becomes cheaper.

In 1900 Count von Zeppelin, a German, built the first
great airship with a petrol-motor attached. Hitherto,
balloons had been used for travelling in the air, but since
they depended on air currents for their movement they
were uncertain and risky to use. The airship still de-
pended on its great gas bags for keeping it afloat in the
air and overcoming the weight of the cars and engines;
but it was now provided with a motor and propeller, and
so could be flown in any direction. This first ship
cost about 10,000, and only remained in the air twenty
minutes. On landing it was utterly wrecked. Count
Zeppelin, however, persevered, and by 1906 had another
airship built which, this time, was more successful.
To-day the German nation owns the famous airshjp, the
Graf Zeppelin, which quite recently has journeyed round
the world and contains cabins fitted with every luxury.

It is the aeroplane, however, which has been most
successful in the conquest of the air. The petrol engine
is used here to draw the machine through the air by
means of the propeller which acts as a screw, hence the
name air screw. The pressure of the air which results
from the high forward speed of the aeroplane acting
on the wings, which are so sloped that the front edge is
slightly higher than the rear, causes upward pressure on
the under surface and a vacuum above the curved upper

THE DEVELOPMENT OF POWER 167

surface. Thus sufficient 'lift' is provided to overcome
the downward force of gravity.

The pioneers in aeroplane construction were two
American brothers, Wilbur and Orville Wright. As
early as 1903 they made a machine which flew two
hundred and sixty yards ; and two years later they made
a flight of twenty-four miles at a speed of thirty-eight
miles an hour. During the Great War (1914-1918)
the use of aeroplanes increased rapidly for military pur-
poses, and since then regular air routes have been set
up between all the important world centres. Hardly a
month passes now without some new record being made.

It is in land transport that the petrol-engine is especi-
ally useful. This is because it takes up comparatively
little room and works automatically once started. The
electric-motor, which is its rival for stationary power,
needs a constant supply of current, and batteries which
might supply this are cumbersome to carry. Elec-
trically-driven vehicles, such as trams and trains, are
therefore always used along definite routes supplied
with lines or overhead wires carrying the current from
a generating station.

These three kinds of engines the steam-engine, the
petrol-engine, and the electric-motor are our main
sources of power to-day. Whether they will still hold
the field a hundred years hence it is not safe to prophesy,

CHAPTER XIII

Waves of Many Kinds

HEAT, light, sound; these are to form the subject of this
chapter. What a dull world it would be without these
three! In fact, take them away and the world would
almost vanish. Imagine a cold, black, silent, world
where the only knowledge of things outside us is obtain-
able by the sense of touch apart from, possibly, taste and
smell; a world where there is no warm sunshine in the
summer or cosy fire in the winter; .where there are no
faces, no colour, no pictures; where there is no speech
and no music. Such a world would be so bleak that we
cannot be too grateful for our senses which are able to
perceive this magic trio.

What is it that we feel when we sit in front of the fire ?
What is it that enables us to see and so makes the world, to
us humans at any rate, such a real thing ? What is it that
our ears hear and our brain understands as speech and
music ? These have been troublesome questions through-
out the ages, and only comparatively recently have any
satisfactory answers been found. Even now our scientists
are finding that there is more to come; we know only
a part.

I
Heat

When, in 1789, Lavoisier drew up a list of those sub-
stances which he considered to be elements, he headed his
list with 'heat' and Might/ In so doing he was in line

168

WAVES OF MANY KINDS 169

with the general opinion of the times which considered
that both heat and light were invisible and weightless
fluids, but nevertheless of definite substance. Very much
the same conception was also held of magnetism and
electricity. Lavoisier gave the name of 'caloric' to that
substance which caused the sensation of heat when it
entered the body.

It is quite clear when we read their books that neither
Boyle nor Newton shared this view of the nature of heat.
Both of them evidently considered that the cause of the
sensation of heat, or of any of the common effects associ-
ated with it, was always motion of some sort. However,
neither laid much stress on this, and so did not change the
prevailing ideas.

Let us now consider some of the most important facts
about heat and its effects :

1 . Heat and Chemical Action. The addition of heat to
chemical substances always makes them react together
more easily. Very often, when two substances react
together to form one or more new substances, quite a large
amount of heat is also formed. Heat is, therefore, in-
timately connected with chemical reaction.

2. Expansion due to Heat. When imparted to any
solid, liquid, or gas, heat nearly always causes expansion,
provided it does not bring about a chemical change.

The old explanation of this was that the fluid heat, or
caloric as Lavoisier called it, pushed its way in between
the particles of which the body was composed, moving
them farther apart and so making the body, as a whole,
take up more room. Galileo used this effect in making
the first thermometer. This consisted of a glass bulb,
with a long glass stem dipping into water which had
previously been made to rise part of the way up the stem.

170

THE ROAD TO MODERN SCIENCE

When the air in the bulb became hotter the air expanded
and pressed the water down the stem. When it cooled, it
contracted and the water rose. Later the expansion of a
liquid, instead of a gas, was used to
show a rise in temperature. We can-
not here follow all the improvements
which were later made in the ther-
mometer. You will easily see a great
many of them for yourself if you look
at a good modern thermometer.

3. Latent Heat. At first little dis-
tinction was made between the 'tem-
perature* of a body and the caloric
which caused it. It was generally
assumed that the addition of caloric
to a body always produced a rise in
temperature. That this was not the
case, however, was first pointed out
by Dr Joseph Black in 1756, just
after he had completed his important
chemical work on the nature of chalk,
quick-lime, and the alkalis.

Two things attracted his attention : the length of time
it takes ice to melt, or boiling water to turn completely to
steam ; and the fact that while either of these changes is
taking place there is no rise in temperature, although heat,
or caloric, is continually being added.

On our modern temperature scale, when ice is melting,
the temperature remains at o C, as long as any ice remains.
When water boils at normal pressure the temperature does
not rise above 100 C.

He explained this extraordinary disappearance of caloric
by supposing that the latter combined with the ice or

FIG. 31. A simple
air thermometer

WAVES OF MANY KINDS 171

boiling water in a kind of chemical combination to form
the new substances, either cold water or steam. It did
this in perfectly definite amounts. Only when the right
amount of caloric had been added for the weight of ice, or
boiling water, was there any further rise in temperature. 1
The caloric which apparently disappeared because of its
combination with the ice, Black called ' Latent ' or hidden
heat.

Black then set about devising a way to measure this
latent heat. His method is the one we still use to-day.
He decided that the best way to measure a quantity of
heat was to find its effect on the temperature of a given
weight of water. He showed that a pound of ice was just
melted by the heat given out by a pound of water when it
cooled from 172 F. to 32 F. that is, to its freezing-
point. In other words, a pound of ice at 32 F. (or o C.)
mixed with a pound of water at 172 F. (or 77*8 C.)
will result in two pounds of water at 32 F. (or o C.).
There were thus two possible units in which caloric
could be measured. The unit might either be:

(1) the amount of heat required to change one unit
weight of ice into a unit weight of water without
changing the temperature, or

(2) the amount of heat required to raise the tem-
perature of a unit mass of water i.

The latter was eventually chosen by scientists as the unit
they preferred to use. To-day the international scientific
unit of heat is the calorie which is the amount of heat

1 It is important to remember that neither the temperature of
melting ice nor that of boiling water can ever be raised by the further
addition of heat. The rise in temperature which finally occurs will be
in the water formed from ice, in the one case, and in the steam from
the boiling water in the other. The latter is often called * super-
heated* steam, and it is above the temperature of boiling water.

172 THE ROAD TO MODERN SCIENCE

required to raise the temperature of one gram of water
from 15 C. to 1 6 C. The unit in everyday use in
England is the British Thermal Unit, or the amount
of heat required to raise the temperature of one
pound of water through i F. The Therm is equal
to 100,000 B.T.U.

4. Heat Capacity. It was already known that different
substances required different quantities of heat to raise
their temperature by the same amount. Another way of
putting this is to say that it was known that some sub-
stances took longer to get hot and cooled more slowly than
others. We all know that water ' holds the heat/ Black's
work showed how a measurement could be made of these
differences. In this way the idea of heat capacity was
introduced. To-day we define the heat capacity of a
substance as the amount of heat required to raise its
temperature through i C. The science of measuring
heat is known as calorimetry. Heat may be weightless,
but it is certainly measurable. Like matter which has
weight, it never disappears so that no trace of it can be
found. As the scientists say, 'it is always conserved/
Because of this, no doubt, Lavoisier felt justified in in-
cluding it in his list of elements.

Count Rumford (1753-1814). The next man to add to
our knowledge concerning heat was that Count Rumford
by whose efforts the Royal Institution was founded, where
Davy and Faraday found such opportunity of distinguish-
ing themselves. Count Rumford was by birth an
American, Benjamin Thompson, and spent his youth in
New England not many miles from that other American,
Benjamin Franklin, the discoverer of the nature of
lightning. As a young man he took part in the American

WAVES OF MANY KINDS 173

War of Independence on the American side; but for
some reason his loyalty was suspected and he fled to
England. After some years his love of a military life took
him to Austria to join in a war in which she was involved,
and later he took service with the Elector of Bavaria who
gave him his title of Count Rumford. On the death of
the Elector he went to live in Paris, where he was treated
with honour by Napoleon, who was invariably hospitable
to men of Science.

Heat Produced by Friction. It was while in Bavaria
that his work in connection with the nature of heat was
carried out. Although in the majority of its reactions
the nature of heat is satisfactorily explained as a weightless
fluid, there was one case which was difficult to explain in
this way. This was the production of heat by friction.
Here heat was produced apparently from nowhere, for no
change could be detected in the bodies between which
the friction occurred. The common explanation during
the eighteenth century was that the friction rubbed or
squeezed out the fluid heat from between the particles of
the bodies. That this explanation did not please either
Boyle or Newton we have seen.

Count Rumford was struck afresh by the problem
when boring cannon in a munition workshop in Munich.
He found that the metal became extremely hot. He care-
fully examined the metal of the cannon, the borers, and
afterwards the brass shavings. He found no change,
however, in the brass of the shavings when he compared
them with the original mass from which they came. He
then carried out a further boring, but with two alterations
in the conditions. He used very blunt tools, and arranged
that the metal should be surrounded with water so that
all the heat produced would go into the water.

174 THE ROAD TO MODERN SCIENCE

The result was that the water got hotter and hotter.
After two and a half hours' boring, to the great amazement
of all the spectators, it actually boiled and remained boil-
ing as long as the boring was continued. This was the
first time, at any rate on record, that water had been made
to boil without the use of fire. Moreover, the supply of
heat was, apparently, inexhaustible, a veritable widow's
cruse.

Heat a Form of Motion. Now Rumford recognised
that although no heat came from outside, something else
had to be supplied all the time. This was motion. The
boring was carried on by the continual movement of two
horses walking in a circle. Rumford, therefore, came to
the conclusion that heat could not be a material substance.
It must be a form of motion. Unfortunately his con-
clusion was not accepted by the scientists generally, their
minds being occupied with other, as they considered,
more weighty affairs at the time.

Sir Humphry Davy. Young Humphry Davy, as he
still was then, was interested, however, and was led to try
an experiment of his own. In this experiment he used
clockwork to produce heat by friction. The machine was
placed on ice in a globe evacuated by an air-pump, and
used to melt some wax. In the ice was a cavity containing
water, which remained unfrozen during the experiment.
According to the old theory, the heat or caloric which
melted the wax must have come from the bodies in con-
tact with the clockwork that is, from the ice. But if the
ice had lost heat, then the water in it would have frozen,
which did not happen. Davy, therefore, concluded that
the heat must have been produced by the motion of the
clockwork.

In this way Davy was converted to Rumford's views.

WAVES OF MANY KINDS 175

He concluded that the friction caused the molecules of
the wax to vibrate and that this vibration was heat. To-
day, this is the view held by all scientists, but it was not
generally accepted until some forty years after the time of
Rumford's and Davy's first experiments.

Julius Robert Mayer (1814-1878). In the year 1840
there lived in a little German town named Heilbronn, not
very far from the famous university town of Heidelberg,
a young doctor named Julius Robert Mayer. He also
was very much interested in this curious appearance of
heat in cases where no corresponding loss of heat could
be found. He recognised that the heat which appeared
during friction was not the only example of such an un-
accountable appearance. Parallel cases were to be found
in the heat which was continually generated in our bodies,
and in the heat generated by the electric current so that
a wire carrying a current could be made to glow. After
long and careful thought on the subject he adopted Rum-
ford's and Davy's view on the source of heat produced in
friction. What is more, he extended it so that it would
cover the two cases we mentioned as well as others which,
on further thought, he realised were similar examples of
the same phenomenon.

Meaning of Work.- In the last chapter we talked at
some length about the meaning of force. A force may act
on a body but will only move it if it is great enough to
overcome the resisting force. Unless the force moves the
body it does not do any work. If it does move the body
we measure the amount of work it does by multiplying
together the amount of force and the distance through
which it moves the body.

Work done = Force x distance (measured in the direc-
tion of the force).

176 THE ROAD TO MODERN SCIENCE

Thus, when the cannon was bored, the work done was
measured by the force used in turning the borer multi-
plied by the distance through which the horses moved.

When work is done we say that energy is used up.
During friction, therefore, energy disappears, but heat
appears.

Forms of Energy. Various kinds of force were known
to Mayer. In addition to the force of gravity, there
were electrical force, magnetic force, the force which
could be exerted by a moving body, and chemical force.
Mayer said that all these different kinds of force were
merely different forms of one and the same thing, which
we now call Energy. To the list he also added heat.
Whenever one of these kinds of energy disappears, said
Mayer, one of the others always appears in its place :

(1) When heat appears during friction it is because
energy of motion has disappeared.

(2) When heat appears in a wire carrying a current
it is because electrical energy propelling the current
has disappeared.

(3) The electrical energy propelling the current only
appeared when chemical force disappeared in the
cell, i.e. when the zinc dissolved in the sulphuric acid.

(4) If the electric current was produced by a dynamo,
then the energy of motion was turned into electrical
energy.

Now, whenever work is done on a body, the energy
used up in doing the work is always stored in the body
and can generally be made to appear again in one or
other of its forms. Generally, in a machine, not quite
so much work can be got out of it as is originally put in,
and up till the time of Mayer there seemed a complete

WAVES OF MANY KINDS 177

loss of a certain amount of work. Mayer, however,
showed that this was not the case. Always there was
developed, whilst the machine was working, a certain
amount of heat because of the inevitable friction between
its parts. This heat, according to Mayer, was the -exact
equivalent in energy of the work which had apparently
been lost. From experiments on the compression of a
number of different gases which had been carried out
by other people, and also from an experiment in a factory
which he arranged himself, Mayer found that in all cases
the heat formed and the work lost were proportional to
each other.

James Prescott Joule (1818-1889). Soon after Mayer
began to work on this subject in Germany, a young
Englishman named James Prescott Joule became in-
terested in the same thing, though quite independently.
He first investigated the heat generated by an electric
current. He was able to find out just how much heat
was generated in a wire if the strength of current flowing
and the resistance of the wire were known.

Mechanical Equivalent of Heat. Next he generated a
current in a wire by means of a small dynamo in such a
way that he could measure the work which was done in
turning the coil of the dynamo. In this way he found
how much work had to be done to develop one calorie
of heat in the wire. This quantity is known as the
Mechanical Equivalent of Heat and is a very important
one.

Joule's early experiments were not very accurate, but
he went on to devise a great many others in which the
heat, developed in all sorts of ways, was measured and its
mechanical equivalent calculated. These experiments
have become very famous. Indeed, Joule won much

12

WAVES OF MANY KINDS 177

loss of a certain amount of work. Mayer, however,
showed that this was not the case. Always there was
developed, whilst the machine was working, a certain
amount of heat because of the inevitable friction between
its parts. This heat, according to Mayer, was the 'exact
equivalent in energy of the work which had apparently
been lost. From experiments on the compression of a
number of different gases which had been carried out
by other people, and also from an experiment in a factory
which he arranged himself, Mayer found that in all cases
the heat formed and the work lost were proportional to
each other.

James Prescott Joule (1818-1889). Soon after Mayer
began to work on this subject in Germany, a young
Englishman named James Prescott Joule became in-
terested in the same thing, though quite independently.
He first investigated the heat generated by an electric
current. He was able to find out just how much heat
was generated in a wire if the strength of current flowing
and the resistance of the wire were known.

Mechanical Equivalent of Heat. Next he generated a
current in a wire by means of a small dynamo in such a
way that he could measure the work which was done in
turning the coil of the dynamo. In this way he found
how much work had to be done to develop one calorie
of heat in the wire. This quantity is known as the
Mechanical Equivalent of Heat and is a very important
one.

Joule's early experiments were not very accurate, but
he went on to devise a great many others in which the
heat, developed in all sorts of ways, was measured and its
mechanical equivalent calculated. These experiments
have become very famous. Indeed, Joule won much

12

178 THE ROAD TO MODERN SCIENCE

more honour and fame for his work than Mayer. It is
one of the blots on the pages of the history of science
that the value of Mayer's work was never properly ap-
preciated at the time it was published. Worse still, when
later he tried to get his work recognised, he was told that
it was not original and that he was only copying somebody
else. It will be agreed that this was a horrible accusation
and was a terrible blow to Mayer. Misfortune also
befell him owing to ill-health and bad treatment by his
fellow-doctors, so that the remainder of his life was very
unhappy. We may be proud, perhaps, that it was one
of our countrymen, John Tyndall, Faraday's successor
at the Royal Institution, who put up a great fight for
Mayer and gained him his deserved recognition during
the last few years of his life.

This great principle which the work of Mayer and Joule
established is always known as the Principle of the Con-
servation of Energy. It states that the sum-total of all
the energy in the world is constant. If energy in one
form disappears, an equivalent amount of another form
appears somewhere else.

II

Sound

Having established the fact that heat is a form of
energy, and not a material substance, let us now turn
to sound. The Greeks seem to have known that sound
was always caused by vibration and that the air was
necessary for its transmission. In the second chapter
in Part I we heard how Pythagoras, listening to the notes
coming from the striking of iron on the anvil, was led
to certain experiments with stretched strings, as a result

WAVES OF MANY KINDS 179

of which he found the connection between the length of
the string and the note sounded.

Leonardo da Vinci went further. He suggested that
sound was carried by waves through the air which were
comparable with waves in water. He explained an echo
as the sending back or reflecting of a wave of sound from
a hard surface, such as the wall of a building or a mountain-
side. By timing the interval between the sending of a
sound and the hearing of the echo, he calculated the rate,
or velocity, with which sound travelled.

Probably Leonardo understood very well the character-
istics of wave motion, but it is Newton who is famous
for his investigations on this subject. His explanation
is difficult, as he invariably talked in mathematical
language. It is very necessary, however, to have a clear
idea of what is meant by this expression, wave motion, in
order to understand the battle which waged over the
question of the nature of light.

It is always simplest to begin with that with which we
are most familiar, so we will make a start with water
waves. If a stone is dropped into a pond, the water all
round the stone becomes heaped up, but as the stone sinks
it returns to its original level. Because of its 'inertia '
that is, because of its tendency to go on moving until
something stops it the surface water slightly overshoots
the mark and sinks below this original level. The water
underneath will only be compressed to a small extent,
however, and quickly succeeds in pushing it back again.
Again, because of its inertia, it overshoots the mark and
heaps up; and the whole process starts again. In this
way the water on the surface, at the point where the stone
sank, oscillates up and down, the oscillations only gradu-
ally dying down. It cannot oscillate, however, without

i8o THE ROAD TO MODERN SCIENCE

disturbing the water round it. A circle of water immedi-
ately around our oscillating point begins to oscillate too,
forced along by the moving water next to it. It starts,
however, just a little later, so that, when the surface water
of the original patch reaches its lowest point, the next
circle has not got quite so far.

In the diagram, XY represents the surface of the
water before the stone was dropped in. Now, let us
consider the surface of the water a few seconds after the
stone fell. The disturbed patch of water, 0, has already
made a number of oscillations. In the diagram the

FIG. 32. To illustrate the principle of water waves. The two posi-
tions are shown by (i) the continuous and (2) the dotted wavy lines

portion has reached the lowest point and is just going
to start moving up again. The portions #, a' on either
side have not quite reached this level and are still moving
downwards; b y V are passing the original level in a
downward direction; c, c' have just reached the highest
point before moving down again; </, d f are passing their
original position but in an upward direction; while e
and e' are portions oscillating exactly in time with the
original portion O. The surface of the water then, in the
direction XY, has exactly the appearance of the continuous
wavy line joining the particles. Now, if we look at the
next diagram, we get an idea of what the whole surface
looks like. The dotted rings join all points which are in
positions corresponding to c and c 1 in the first diagram.
Together they form the * crest* of the waves. The black

WAVES OF MANY KINDS

181

rings join all points in positions corresponding to e, e'
which form the troughs.

Now turn back to the figure 32 and let us consider the
surface a moment later, as shown by the dotted line.
O has now reached the original level moving in an upward
direction. The portions d and d' now form crests which

FIG. 33. The dotted lines represent crests, and the
black lines troughs

have moved outwards away from O. The spread of
ripples outwards from the point where a stone sinks is a
familiar sight to all. It is most important to realise that
the actual water does not move outwards at all, but only
up and down along the same vertical line. It is only the
wave or shape of the surface which moves outwards.

When a tuning-fork is sounded, waves of sound spread
out in all directions through the air. The vibrations of
the tuning-fork make the particles of air round it vibrate ;
these affect the next layer and so on. The vibration thus
spreads outwards till finally the layer of air in contact

182 THE ROAD TO MODERN SCIENCE

with the drum of our ear is set vibrating. The drum of
the ear is made so that it also can take up the vibration
and transmit it to the brain, when a * sound ' is heard.

There is one important difference between sound waves
and water waves. The particles of water, as we have
seen, vibrate in a direction at right angles to the way in
which the waves are travelling. The particles of air,
however, vibrate in the same direction. What really
happens is that, as the prongs of the tuning-fork move
outwards, they compress the air all around. This com-
pression is passed on to the next layer, and the next, and
so on. We say that a pulse, or wave of compression, is
sent out. As the prongs of the fork move back, however,
the air can expand again and so a pulse of ' rarefaction '
quickly follows the one of compression. Galileo showed
that the more quickly these pulses followed each other
the higher was the note sounded.

Except for the direction in which the particles vibrate,
there is no essential difference between the wave motion
in air which causes sound and wave motion in water.
As we have seen, Newton studied the question of wave
motion very carefully. One of the most important
results of this study was that he showed that the rate
at which sound travels through the air depends upon the
temperature of the air, the barometric pressure, and the
amount of water vapour in it. He also showed how to
calculate this velocity for a given set of conditions.

Although sound, as a rule, travels through air to reach
our ears, it will pass through other forms of matter as
well. It generally does so at a faster speed. There
are many stories of Red Indians who, by holding their
ears close to the ground, hear sounds of horses a great
way off. The sound travels quickly through the earth,

WAVES OF MANY KINDS 183

and does not get deflected or absorbed by obstacles. In
travelling through the air it meets solid obstacles which
either absorb it or else reflect it off in another direction.

Ill

Light

The nature of sound, then, was fairly well understood at
the time of Newton. The same could not be said about
the nature of light. Let us quickly summarise what was
known as to the properties of light.

(1) It appeared to travel in straight lines that is,
it cast sharp shadows and did not bend round corners.

(2) It would pass through some kinds of matter
transparent bodies, but was absorbed by others
opaque bodies ; while a third kind reflected it back.

(3) When light was reflected from a surface, the
angle at which the ray struck the * mirror ' was the same
as that at which it was reflected.

(4) When light passed from one transparent medium
to another it was bent or refracted. It took a long
time to find the rule showing just how much the ray
was bent; but just about twenty years before Newton
was born a Dutch professor named Willebrord Snell
had discovered this rule.

(5) A Danish contemporary of Newton's, Olaus
Roemer, showed from his astronomical observations
that, although light travelled very quickly, far more
quickly than sound, it did take a definite time to travel.
For a long time it had been thought that it travelled
instantaneously.

(6) We have already seen how Newton himself
showed that white light can be split up into colours by
passing it through a prism.

184 THE ROAD TO MODERN SCIENCE

All this tells us quite a lot about what light does but very
little about what it is. .

The popular theory at that time was that light con-
sisted of streams of very fast moving tiny particles travel-
ling in straight lines. These particles would rebound
from certain surfaces just as a ball rebounds when it
strikes a wall obliquely. They would change their speed
when going from one medium to another, and this would
cause them to change their direction, or become refracted.

FIG. 34. Showing the refraction of light in glass

Christian Huyghens (1629-1695). During the first half
of Newton's life there was living in Holland an older man
who advanced an alternative theory as to the way in which
light travels. This man's name was Christian Huyghens
(pronounced Hoygens). There is not much to tell about
his life ; he had plenty of money and could devote himself
to the study of mathematics and science.

Now Huyghens saw one objection to what was known
as the * Emission* or Corpuscular Theory of Light (that
is, that the source of light emitted streams of corpuscles).
If two streams of particles crossed one another's paths,
the particles would collide and fall to the ground. For
instance, it would be difficult to see how two people could
look straight at each other without the rays of light by

WAVES OF MANY KINDS 185

which they saw each other, colliding and stopping
half-way.

Huyghens, therefore, suggested that light, instead of
consisting of moving particles, was similar to sound and
travelled in waves. These could cross each other and
still go on undisturbed. There was this difference,
however. While sound could not pass through a vacuum
it was known that light could. Now waves must travel
through something; there must be particles to vibrate
and so transmit the waves. Huyghens, therefore, saw
that, according to his theory, when every kind of matter,
even air, has been removed, space still contains something
which can vibrate. This something he called 'Ether.'

Huyghens was able to show, by mathematics, that if
light really consisted of a train of waves it should show all
its observed properties except that it should bend slightly
round corners of objects in its path, instead of casting
sharp shadows as it appears to do. This last seemed a
very important objection to Newton. He examined
shadows very carefully and could see n'o blurred edge in
those cast from a point source. If the light really spread
out round the corners, the edge of the shadow should be
slightly blurred.

Newton, therefore, made up his mind that this objec-
tion was more important than the one Huyghens raised
against the Emission Theory. He argued that if the
particles in the latter were very small, the chance of their
colliding would not be nearly so great. Newton, himself,
probably never definitely made up his mind in favour of
either theory. Certain of his writings were, however,
misinterpreted as deciding definitely for the Emission
Theory.

Newton's genius was so greatly respected that this

186 THE ROAD TO MODERN SCIENCE

reputed decision was accepted both by his contemporaries
and his successors. During the whole of the eighteenth
century the universal conception of a ray of light was of a
stream of tiny particles or corpuscles moving in straight
lines with extremely high velocity. Huyghen's Wave
Theory lay forgotten and discredited until it once more
found an adherent in Thomas Young at the beginning of
the nineteenth century.

Thomas Young (1773-1829). Thomas Young was born
in Somerset in 1773, and appears to have been an infant
prodigy. He could read at the age of two, and at six was
reading books which most people left till a much riper
age, if, indeed, they read them at all ! He qualified as a
doctor, but, being comfortably off, he did not practise to
any great extent.

During his medical training he became very much
interested in the anatomy of the eye and the power of
vision. From that it was a short step to the nature of
light itself. For two years, from 1802 to 1804, he also
was a lecturer at the Royal Institution. It was during
this period that he gave to the public the conclusions
he had come to on this subject. Unfortunately, Lord
Brougham, who afterwards became Lord Chancellor of
England, also dabbled in science. He took it upon him-
self to ridicule the views of Young in some articles which
appeared in a very celebrated magazine, the Edinburgh
Review. As is so often the case, the power of ridicule and
satire is strong, and Young's views received no further
notice from the scientific world for the time being.

In studying the question of the nature of light, Young
read the books of both Newton and Huyghens. In
pondering over the merits of the rival theories he saw that
certain things could be predicted from the wave theory

WAVES OF MANY KINDS 187

which could not take place if the Emission or Corpuscular
theory were the true one. He arrived at this conclusion
by considering what would happen if two sets of similar
waves, moving with the same velocity, crossed the surface
of a still lake and met in a narrow channel leading from
the lake. The effect produced on the water in the channel
would obviously be the joint effect of the two sets of waves.
If they met in such a way that the crests of one set coin-

/jyvxA/xA/j^yvvvvvv

i i ,

Ai/wwv \iA/vww\

cresf

Crtsf OH

FIG. 35. Showing the combined effects of two trains of waves

cided with the crests of the other, then crests of twice the
size would be formed. If, on the other hand, the crests
of one set coincided with the troughs of the other, then
these would neutralise each other and the water would
remain smooth.

Young's next step was to see whether he could produce
such an effect with light. Could he, in any circumstances,
' add light to light and get darkness ? ' If he could, then,
in his view, the issue between the two theories would be
settled in favour of that of Huyghens. This is how he set
about it.

He produced two small sources of light by pricking
pinholes close together in a visiting-card and letting light

1 88

THE ROAD TO MODERN SCIENCE

from a single source pass through the holes. In this way
the effect, on the other side of the card, would be as if the
light were coming from two sources. In the diagram (S)
is the original source of light ; (A) and (B) are the two pin-
holes. (C), (E), (D), and (F) is a screen on which the
light is received. Now, if light consists of corpuscles,
then the whole of the patch C, F should be illuminated,
but E D should be twice as bright as C E and D F, since
it receives light from both A and B. Suppose, on the
other hand, Huyghens was right. From A and B two

FIG. 36. Illustrating Young's experiment

trains of waves would meet between E and D. The
resulting light would be the combined effect of both sets
of waves. Where a crest of one wave coincided with a
crest of the other the light would certainly be twice as
bright. But at other points crest would meet trough, and
the result would be darkness. In this case one would
expect both light and dark patches on E D.

Young viewed a small and rather distant source of light
through the pinholes, so that his eye corresponded with
the screen C E D F. The light then appeared as a patch,
bright round the edges, but with the centre crossed by
dark bands. The experiment had decided in favour of
Huyghens and the Wave Theory of Light.

As we have seen, although Young himself was con-
vinced, he did not succeed in convincing anyone else.

WAVES OF MANY KINDS 189

Augustin Fresnel (1788-1827). Luckily, a dozen years
later, a younger Frenchman named Fresnel, working
independently along the same lines, demonstrated by a
still better experiment the ' interference ' of light, as the
production of dark bands in the manner described is
called. His results were received with proper respect
by his countrymen. As he was able to back up his
experimental result with a mathematical argument, dear
to the heart of every scientist of that day, the Wave Theory
of Light was almost immediately universally accepted.
Until his work was published, Fresnel had not known of
Young's earlier proof ; but immediately he heard of it he
wrote to the latter at once acknowledging his priority.

Fresnel is usually acknowledged to be the founder of the
Wave Theory of Light, as he undoubtedly produced the
fullest and most convincing proof of its truth. It is
impossible to follow the proof here. In addition, he
showed that Huyghens' original suggestion that the wave
motion of light is similar to that of sound (except that it
travels in a different medium) must be altered in one
particular.

It had been known for some time that a ray of light
behaved in rather a peculiar way when it passed through
certain kinds of crystals. It split into two rays. Fresnel
showed that this peculiarity could be fully explained if
light waves were compared with water waves rather than
with sound waves. That is to say, the vibrations of the
ether must be imagined as taking place at right angles to
the direction in which light is travelling, and not in the
same direction. Proof of this also is too complicated to
go into here, but the result is very important to remember.
We usually describe the vibrations of light as * transverse '
and those of sound as 'longitudinal.'

i 9 o THE ROAD TO MODERN SCIENCE

It ought perhaps to be mentioned here that, after all,
the Wave Theory has not been able to explain everything.
New facts discovered by modern physicists have led to
the adoption of a theory which is a combination of both
the Emission and the Wave Theories.

IV

The Spectrum

We must now see how this new wave theory explains
the colours which are obtained when white light passes
through a prism. Newton had supposed that the
particles of the seven colours of light were of different
sizes, those of the violet being the smallest and of the red
the largest. According to the new theory the waves of the
violet light were the shortest and the waves of the red light
the longest. The length of the wave is measured from
one crest to the next one. All light waves are very short
indeed ; about 5000 go to i centimetre.

Radiant Heat. In 1800, just before Young had
published his ideas on the nature of light, Sir William
Herschel, an astronomer of whom we shall hear more
later, placed the bulb of a very sensitive thermometer in
various parts of the spectrum obtained by passing sun-
light through a prism. He found that in all parts of the
spectrum there was heat falling on the screen, the rise in
temperature increasing as the thermometer was moved
from the violet to the red end. He then tried putting the
thermometer just outside the spectrum. At the violet
end there was no rise in temperature, but the thermometer
was affected over a distance of i\ inches beyond the red
end. This meant that as well as light rays coming
through the prism there were also invisible heat rays, some

WAVES OF MANY KINDS 191

of which were bent less than the red rays of light. When
the wave theory was established it was realised that these
heat waves were really just the same as the light waves,
except that their wave-length was a little longer. It is
the peculiarity of our bodies which makes us * see ' certain
wave-lengths as light, but only feel others as heat. There
is nothing essentially different in the waves themselves.

Heat is always a form of energy, but it does not always
consist of waves in the ether. When anything is hot the
molecules of which it is composed are moving more
rapidly than they were when it was in a cooler state.
The molecules are never absolutely still. If they were,
the body would possess no heat ; its temperature would be
at absolute zero, which is 273 C. below the freezing-point
of water. Such a low temperature has never been reached.
The movement of the molecules in a solid is a kind of
vibration, the molecules keeping their same relative
position. In liquids the movement is more at random;
and in gases the molecules move very rapidly in all
directions.

The violent motion of the molecules of a very hot body,
such as the sun, disturbs the surrounding ether, and
waves of ' radiant heat' are sent out in all directions.
When these waves meet some other body they give up
their energy to its molecules which, therefore, move
faster than they were doing, and so the temperature of this
body rises. Gases, as a rule, are not able to absorb
radiant heat. That is why the heat from the sun passes
through the envelope of air without heating it and is not
absorbed until it reaches the earth. A cloud, however, is
able to absorb a certain amount, and so shuts off the heat
of the sun from the earth. Radiant heat obeys just the
same laws of reflection and refraction as light rays.

i 9 2 THE ROAD TO MODERN SCIENCE

Ultra-violet Rays. If you know anything about photo-
graphy you will probably know that certain chemical
substances, such as silver chloride and silver bromide,
are darkened on exposure to light, and that this fact is
made use of in taking photographs. The year after
that in which Sir William Herschel found that the
spectrum extended beyond the red end, it was found that
there was also an invisible portion beyond the violet end,
which, although it could not be seen, would still darken
silver chloride paper. These new rays became known
as the ultra-violet rays and the radiant heat rays were
generally called the infra-red rays. Thomas Young
measured the wave-length of these new ultra-violet rays,
and found, as might be expected, that their wave-length
was shorter than that of the violet light. It has since
been found out that it is the ultra-violet light from the
sun which possesses the health-giving properties.
Ordinary glass absorbs these ultra-violet rays, but a
certain kind of glass called * vita-glass ' lets them through,
so that it is a very good thing, if one can afford it, to have
windows fitted with this glass.

X-rays. The existence of ultra-violet rays was dis-
covered in 1801. In 1895, nearly a hundred years later,
it was discovered that the spectrum extended even beyond
these. In that year Professor Rontgen of Wiirzburg
discovered the rays which were first known as Rontgen
rays but now are more usually called X-rays. These
rays consist of very rapid vibrations in the ether, travelling
in very short waves. They are very penetrating and will
pass through most solid material with the greatest of ease.
Only several inches of lead can be depended upon to stop
their passage entirely. A few years after Rontgen dis-
covered his rays it was found that the same kind of rays

PLATE XVIII

HersehePs Giant Telescope

A Spiral Nebula

WAVES OF MANY KINDS 193

were being given off continually from all radio-active
substances. The best known of these, of course, is
radium. As you know, radium is now used by doctors
in their efforts to cure certain diseases, such as cancer.
Great care has to be exercised in its use, because the
radiation which it emits is very powerful and causes bad
burns if it touches the flesh. Accordingly, it is always
kept in lead tubes, and, when not in use, is surrounded
by blocks of lead and kept carefully locked in a safe under
one person's charge.

The rays given off from radium are of even shorter
wave-length than Rontgen rays, and possess greater
penetrating power. Rontgen rays are used for taking
X-ray photographs. A stream of rays is sent through
the limb, say, which is to be photographed, and allowed
to fall on a photographic plate. The denser parts, such
as the bone, stop the rays to a greater extent than the
flesh and muscle, and this difference shows up on the
plate, so giving a picture of the inside of the limb. Many
shoe shops keep an X-ray instrument, where you can see
this for yourself.

Wireless Waves. Finally we come to the 'wireless'
waves or radio in such constant use to-day. Maxwell
had predicted that such waves could be produced, and
a German professor, Heinrich Hertz, actually obtained
them in 1887. In 1901 an Italian named Marconi showed
that they could be put to practical use by sending messages
in the morse code from England to Newfoundland.
During the twentieth century innumerable scientists and
engineers have been at work on the subject, with the
result you know very well. Day and night, all over the
world, waves are being sent out from innumerable broad-
casting stations, and picked up by the receiving sets in

13

194 THE ROAD TO MODERN SCIENCE

countless homes. Here, by means of the head-phone,
or loud-speaker, they are turned back into sound waves
exactly similar to those which originally produced them.

Now these wireless waves are similar in nearly every
respect to light waves. They are caused by vibration
set up in the ether, and they travel with exactly the same
speed as light. The essential difference between light
waves and 'wireless' waves is that, while the distance
between two 'crests' in a train of light waves is only a
fraction of a millimetre, that between two crests in a
train of wireless waves is some hundreds of metres.
The wave-length of the waves sent out from Droitwich.
giving our National Programme, is 1500 metres, while
the London Regional programme is sent out on a wave-
length of 342 metres. Lately, much shorter wave-
lengths have been used by some stations, but they are
all very big indeed compared with those of light.

All the other kinds of waves, of which we have spoken,
affect some part of our bodies, but, at any rate, to our
knowledge, wireless waves have no effect whatsoever
upon us. They can, however, be made to affect an
electrical instrument that is, a wireless receiving set.
This effect is then transmitted to the diaphragm of the
earphone or loud-speaker, making it vibrate and emit
sound waves. At the transmission station the reverse
happens. Sound waves, emitted by the person broad-
casting, for example, make the diaphragm of the micro-
phone vibrate. This diaphragm is connected with an
electric circuit, and its vibrations are passed on to the
current. Vibrations in the current electric pulses they
may be called send out magnetic pulses in the ether.
These are the wireless waves.

No radiation of wave-lengths between those of the

This table shows the rela-
tive sizes of various objects
which we observe and
measure. It is like a set
of shelves on which we
place specimens of objects
(1-5 x 10 J3 ) which vary in size from the
very great to the very small.
On the middle shelf marked
jo zero, we have the centi-
w (4 x 10 ) m etre, an d tne thickness of
Diameter of the earth 0-3 x JO 9 ) a pencil to represent objects
of that order of magnitude.
On the shelf above we place
an object of about ten centi-
metres in size ; the width of
g street a nan d will serve. The shelf

|gr above takes objects of about

a hundred centimetres, for
* example small objects of

furniture. The width of a
h street will represent a thou-

MM of a pencil sa f nd centimetres the height
of a tower might be ten
Cflr ^ thousand centimetres or a

r hundred metres, and so on.

Below the zero shelf comes
first a shelf holding something of a milli-
metre in thickness, as a card; then the
hair's breadth on the next shelf and so on.
Bacteria are at various heights on the
third and fourth shelves down ; molecules
on the sixth and seventh, atoms nearly
down to the eighth. On the other side
of the vertical line the various wave-
lengths are shown against the objects to
which they correspond. Distances are
sometimes given in figures. The sun's
distance is fifteen million million centi-
metres, or in symbols 1-5 x io 13 . This goes
therefore on the thirteenth shelf up.
(From The Universe of Light, by permission of Sir William Bragg.)

18

Nearest stars

17

16

15

14
13

_ Distance of thi

12

11
10

__ Distance of th

9

Diameter of th

8

7

6

A distant view

(5

Kilometre. A Ic

Radio waves { 4

Height of a to

(3

Mdthofastr

2

Metre. A chair

1

A hand's breai

Centimetre. Thk

1

Thickness of a

2

A hair's bread

3

Infra red wanes 4
Visible waves
Ultra uiolet waves 5

\Bacteria

%

6
7

X rays 8
y rays 9

~~ I Molecules
_ Atoms

Cosmic rays ?

M

12

13

Atomic nuclei

14

196 THE ROAD TO MODERN SCIENCE

shortest wireless waves and the longest heat waves are
known. There is a big gap in our knowledge of the
greater spectrum here, but it will probably be filled up.

As it is, wireless waves are continually being made
smaller and smaller. The new Micro- Ray, which has
recently been put into use for sending messages about
aeroplanes, has a wave-length of less than a centimetre.
At the other end the spectrum is quite continuous and
there is no gap to be filled. Certain rays, known as
Cosmic rays, are receiving much attention at the present
time. It appears that they are shorter than any waves so
far investigated.

The discovery of this continuous series of waves is a
very wonderful one. Still more so is the thought that
the greater part of the world we live in is made up of
these vibrations. Some scientists even suggest that the
whole physical world may originate in them; but, per-
haps, even if they decide that it does, it will not affect
us very much !

CHAPTER XIV

Astronomy
i

IN the first part of this book we saw that the old con-
ception of the Earth as centre of the Universe gave place,
during the sixteenth and seventeenth centuries, to a new
one. In the new doctrine the Earth was removed from
its position of pre-eminence and relegated to one of
comparative unimportance, becoming merely one of the
planets which revolved round the Sun. In the new
astronomy the Sun thus became the centre and most
important heavenly body. Moreover, in the hands of
Newton, the last of the giants who worked for the
overthrow of the old system, the paths and motions of
the planets were fully explored and the laws governing
these motions established. In fact, from this time on,
astronomers felt that they knew all about the Solar
System.

In one respect, however, the old doctrine remained
unchanged. The planets were still supposed to revolve
against a spherical background containing the fixed stars ;
and the sun was, tacitly, assumed to be the centre of the
whole universe. We have now to see how this assumption
was, in its turn, to be proved to be quite unjustified.

Sir William Herschel (1738-1822). The story of the
exploration of the * Fixed Stars ' is a thrilling one, for it
was carried out by a man quite untrained in Science and
Mathematics who took to the study of the heavens purely
as a hobby. William Herschel was born in 1738 in

197

198 THE ROAD TO MODERN SCIENCE

Hanover. He was the son of a bandsman in the Hano-
verian Guards, and followed his father in that profession.
When he was about seventeen years old the Hanoverian
Guards were called to England, for the Hanoverian
Georges were now on the throne of this country. Two
years later Herschel left the Guards, and after a number
of musical positions in various towns in England settled
finally in Bath as organist of the Octagon Chapel there.
Bath at that time was a very fashionable place, and
Herschel was soon drawn into the full swing of the
musical life of the town. Besides holding the position
of organist he taught a great number of pupils, and also
wrote compositions of his own. Despite a hard day of
about fourteen hours, however, he would spend half the
night in various other kinds of study, such as Italian,
Greek, Mathematics, and Optics. Then a book on
astronomy came his way, and he turned with great zest
to this new pursuit.

When he was about twenty-five his father died in
Hanover, and Herschel suggested that a younger brother,
Alexander, should come over to join him in England.
The Herschels were a large family and all were musical ;
but Alexander was also very clever with his hands and,
in this way, was to prove himself very useful to his
brother. There was, also, a much younger sister,
Caroline, who was devoted to her brother William, and
he to her. Her mother was a firm believer in keeping
her daughters well occupied with housework and needle-
work, and allowed them to have no other kind of educa-
tion. For some time the two brothers in England made
great efforts to get their mother to allow Caroline to join
them, but it was not until seven years later that, finally,
William succeeded in bringing her over to England.

ASTRONOMY 199

Here she led a very different life, for not only did she
do the housekeeping for her brothers, but she also herself
had singing lessons and took her part in their musical
life. This, still, was not all, for by this time Herschel
was filled with the ambition to see for himself the wonders
of which he read in his books on astronomy. He hired
a small telescope, but was soon dissatisfied with it, and
determined to make one for himself. The pattern used
at that time was the one designed by Newton, which is
generally known as the reflecting telescope, for which
a very large spherical mirror l was required.

The Herschels' house now was turned upside down
and filled with tools and polishers of all sorts with which
the two brothers proposed to make the telescope. At the
same time, they had to carry on with all their musical
work. Their time was so crowded that it even came to
Caroline having to feed her brother while he ground and
polished his mirrors! Finally, however, in 1774, when
he was thirty-six years old, Herschel finished his first
5^-foot telescope, and began viewing the heavens with
it. He at once started to make another telescope, how-
ever, and this was followed by still another larger one.
In fact he was never satisfied. His ambition was to make
a zo-foot instrument.

With his first telescope he began a systematic survey
of the heavens; what is technically called ' sweeping '
them. This is a very slow and tedious business, for
every bit of the sky has to be examined with the utmost
care. Each individual star has to be noted, described,
and its exact position ascertained. During his lifetime

1 A spherical mirror may be conceived as a slice cut off a hollow
sphere. The reflecting surface may be either the inner or the outer,
i.e. the mirror may be concave or convex. In this case the mirror was
concave.

200 THE ROAD TO MODERN SCIENCE

Herschel carried out this operation, passing the whole of
the heavens under review four distinct times !

He soon began to find out some new and extremely
interesting things. Even with the naked eye, of course,
it can be seen that the stars are not all of the same bright-
ness. With his powerful telescope Herschel discovered
many more differences. Some stars he found were
'variable' in their brightness. Again, stars differed
from each other in their colour. Most interesting of all,
he found that many were really 'double/ two stars
revolving round each other.

In some parts of the sky he found what he called
' nebulae/ These were bright luminous patches in the sky.
He found it difficult to explain these, and so did other
astronomers when they saw them. (See Plate XVIII.)

He began writing about all these discoveries, and in this
way built up a considerable reputation.

In 1781, however, he discovered something which
immediately made him really famous. This was a new
planet ! How did he know it was a planet ? Chiefly by
its size, because it appeared to be so much bigger than
the other stars. This meant that it was much nearer.
Then, also, its position continually altered with reference
to the others. At first he thought it was a comet, in
which case it would move in a very long ellipse and vanish
from sight for a considerable period.

Directly they heard of the discovery professional
astronomers turned their telescopes on the star, and set to
work to calculate its path or orbit. This, they found, was
almost a circle round the sun. It was therefore a new
planet ; more than a hundred times as big as the earth and
nearly twice as far away from the sun as Saturn, the outer-
most of the other planets. This was, indeed, a startling

ASTRONOMY 201

discovery. For centuries the number of planets had been
taken as one of the fixed things of nature and of special
significance.

The new planet was called Uranus, and it and its
discoverer became the talk of the day. The King,
George III, sent for Herschel and his telescope to Windsor
to show the Court the new planet. The Astronomer
Royal, on seeing the telescope, declared that the one at
Greenwich was not to be compared with it. Finally, the
King appointed Herschel to be astronomer and telescope-
maker to himself, and Caroline was sent for to set up
house near Windsor.

So many people wanted telescopes that Herschel soon
wearied of making them, for he got no time for his own
observations, nor to make a better instrument for himself.
The King heard of this, and ordered that a gigantic tele-
scope be made for Herschel's own use. This was done,
and a wonderful instrument, costing finally 4000, was
built. (See Plate XVIII.) With this he continued his care-
ful study of the heavens. His sister, Caroline, spent more
time than ever helping him, taking down observations and
also making discoveries with a telescope of her own. Even
when Herschel married and she removed into lodgings she
still came across every night to help with the observations.
The telescope was erected outside, and they worked every
clear night, even when the temperature was many degrees
below freezing-point. Night was turned into day.
Luckily they both seemed to have very good constitutions,
for Herschel lived to be eighty-four and Caroline to be
ninety-eight !

Herschel continued to make discoveries. During his
lifetime he discovered 806 double stars and 2500 nebulae.
He found that, after all, the stars are not fixed, but move

202 THE ROAD TO MODERN SCIENCE

slowly among themselves, and he measured this motion.
He realised that the sun of our solar system is but one
among many such. The solar system, indeed, is a mere
speck in a universe, almost vaster than mind can conceive.
Moreover, the sun is by no means one of the biggest stars.
Sirius is twenty times larger. Further, he found that
even the sun is not fixed, but is moving rapidly through
the heavens.

One thing he tried hard to do but failed in. This was
to measure the vast distances between the stars. This,
as we shall see, was done later. Even so, his achievement
was tremendous. He had shown that what, to the naked
eye, looked like a flat background on which were painted at
intervals fixed luminous points was, in reality, a vast space
through which were moving, probably at tremendous
speeds, myriads of stars compared with which our sun,
with its satellite planets, shrank into insignificance. This
Herschel achieved by dint of unlimited enthusiasm,
unlimited energy, and unlimited patience. Nor must
we forget the loyalty, zeal, and enthusiasm of his indefatig-
able sister, Caroline. Such a pair is not often to be met
with in the annals of history.

Laplace (1749-1827). Contemporary with Herschel,
although born some ten years later, was a very clever
French mathematician and astronomer named Laplace.
He belonged to that extraordinarily brilliant group of
French scientists that characterised the era of Napoleon
Bonaparte and the years immediately succeeding it. He
was essentially a mathematician. He continued Newton's
work in calculating the effect of the various planets on
each other, for Newton's Law of Gravitation applies not
only to the attraction existing between the planets and the
sun, but also to that between the planets themselves.

ASTRONOMY 203

The forces in the latter cases are, of course, smaller. But
they are none the less important, for small forces con-
tinually exerted may have great consequences.

There was a question, raised by Newton himself, as to
whether the solar system was quite stable. That is,
would the planets always move in just the same way, or
would they get nearer or farther away from the sun ? If
the former, it might happen that one of them would
eventually fall into the sun, in which case the heat de-
veloped would be so tremendous that it would be the end
of life on this planet at any rate.

Another astronomer, named Halley, who was con-
temporary with Newton, had searched old documents
and star-maps from the very earliest times for the positions
of the various planets and the times of eclipse of the moon.
It was quite possible from the Law of Gravitation and the
known positions of the planets at the time (i.e. Newton's
and Halley's time) to calculate where the planets should
have been at the time given in the old maps ; and when each
eclipse should have occurred. This was done, but the
results did not agree with those recorded.

Laplace, however, attacked the problem with the help
of another mathematician, Lagrange. These two were
able to show that the disagreement was due to the fact
that the effect of the planets on each other was not allowed
for in calculating the early positions. When this was done
there was good agreement. Furthermore, Laplace was
able to show that although the paths of the planets round
the sun have quite definitely changed during the thousands
of years over which records have been made, yet the
changes have been rather like the swings of a pendulum,
sometimes towards and sometimes away from the sun.
There is no danger of the planets falling in on the sun and

204 THE ROAD TO MODERN SCIENCE

destroying the solar system, as things are at present. We
express this fact by saying that the solar system is 'in
equilibrium.' Of course, if anything from outside were
to upset it, that would be a different matter.

In considering the solar system, Laplace was struck by
some rather extraordinary coincidences.

Firstly, the direction in which the planets were moving
round the sun was the same in every case. Moreover, the
satellites each moved round their own planet in this same
direction. Secondly, the orbits of the planets and their
satellites were all in very nearly the same plane. By that
is meant, that if the plane of the ellipse in which the earth
moves were extended indefinitely, it would be found to
include also the paths of the rest of the planets round the
sun, of the moon round the earth, of the moons round
Jupiter, and of the rings round Saturn.

Pondering on this, Laplace came to the conclusion that
at one time the sun and the planets, and their moons,
must all have been part of one gigantic mass rotating in the
same direction. If this were the case, however, the matter
of which they consisted must have been very much rare-
fied that is, spread out, for the solar system occupies a
tremendous space compared with the masses of the sun
and planets to-day. This matter must, therefore, have
been in the gaseous state.

By this time Herschel had begun to make his discoveries
of the nebulae in the heavens, and astronomers had come
to the conclusion that they were just such masses of
rotating gas. Laplace, therefore, suggested that the solar
system had originally been one of these glowing gaseous
nebulae rotating in space. By now, also, physics had so
far advanced that it could be shown that such a rotating
mass of vapour, as it cooled, would shrink and separate on

ASTRONOMY 205

the outside into rings which would go on rotating with the
central mass. As these rings cooled they would divide
into fragments, which later would probably collide and
form one mass which would still go on rotating. The
smaller of these masses would cool quickly and become
first liquid and then solid, while the larger masses would
retain their heat longer. The central mass, of course,
formed the sun, and the outer rings shrank and coalesced
to form the planets.

This theory is always known as Laplace's Nebular
Hypothesis, and was held to be the probable explanation
of the origin of the solar system for more than a century.
Recently, however, another explanation has been put
forward, which is more in accordance with the wider
knowledge of the present day. The origin of the solar
system, and indeed of all stars, is still supposed to be one
of the nebulae. In course of time these nebulae gradually
condense and cool as they revolve, and usually they
eventually divide into two halves, which go on revolving
round each other, forming one of Herschers 'doubte
stars/ An accident, however, happened to the star which
is our sun. Herschel had found, you remember, that the
stars are not fixed but are moving through space. The
distances between the stars are so vast that they rarely
come near enough to have any effect on each other; but
in the case of our sun it is supposed that such a thing did
happen. Some other star, in its journey through space,
approached our sun so closely that the attraction between
the two masses tore great chunks out of the sun. These
masses were carried on round with the central mass left,
and so formed the planets. This is the explanation held
to-day.

The Discovery of Neptune. After the discovery of

206 THE ROAD TO MODERN SCIENCE

Uranus by Herschel, astronomers began to wonder
whether this planet had really previously been seen by
any other observer, but not recognised as differing from
the fixed stars among which it moved. Accordingly the
maps of various earlier astronomers were searched. The
object was to see whether they recorded the position of
any star agreeing in brightness and magnitude with
Uranus, which was not in that position now. In this way
it was found that Uranus had been seen and catalogued
altogether twenty times! But no one had exercised the
care that Herschel had used in comparing observations
taken at different times. So Uranus had never been
recognised as a planet.

These older records were now useful in finding, or
'computing' as it is called, the exact path of this new
planet. After a time it was found that it did not travel
exactly the path calculated by the Law of Gravity. The
calculations took into account the effect of the other
planets as well as that of the sun. Here was a new
problem for astronomers to solve.

Two explanations were suggested. One was that
Newton's Law of Gravity was after all not exact and that
Uranus only obeyed it approximately. The second was
that, somewhere, there was another large body, probably
another planet, farther away from the sun, which was
pulling Uranus slightly out of its path. This last explana-
tion was all very well, but the puzzle was where to look
amongst all the vastness of the sky for this unknown
planet. But found the planet was; and its finding was
one of the greatest achievements of mathematics.

John Adams. The man who first showed where it was
to be seen was a young Cambridge graduate, Senior
Wrangler of his year. That is, he headed the list in the

ASTRONOMY 207

examination for the Mathematical Tripos in the uni-
versity. His name was John Adams. Fresh from the
victory, he set himself the task of solving the problem of
the 'perturbations' of Uranus.

It was a mathematical problem, the like of which had
never before been attempted. Here was Uranus being
pulled out of its path by an absolutely invisible agent,
and Adams had got to find the size and whereabouts of
the latter just with a pencil and paper. Well, he did it.
Then he wrote to the Astronomer Royal and told him
that if he pointed his telescope at such and such a point
in the sky, at such and such a time, he would see the new
planet which was upsetting Uranus.

It might be expected that the Astronomer Royal
would have been very interested in this information to the
exclusion of everything else. But he was constantly
getting letters telling of wonderful new discoveries, nearly
all of which proved to have nothing in them. Besides,
Adams was a very young man. So all the Astronomer
Royal did was to write to Adams and ask him if his new
planet would explain something else which was not quite
understood. Unfortunately, Adams did not bother to
answer this question, and so nothing more was done about
his discovery.

In the meantime, a young French astronomer, Leverrier,
was at work on the same problem, and he also solved
it successfully. Eight months after receiving Adams'
letter, the same Astronomer Royal of England received
a letter from this Frenchman, Leverrier, giving a position
for the new planet within i of that given by Adams.
After all, he thought, there must be something in it.
However, he put the same question to Leverrier as he
had to Adams, and this time, since it was answered

208 THE ROAD TO MODERN SCIENCE

promptly and satisfactorily, he decided to search for the
planet.

His telescope, however, was occupied in other ways,
so he wrote to the professor at the Cambridge Observatory
asking him to make the search instead. A steady sweep
of the heavens in the direction advised was then started
and all stars of the right magnitude noted. To make
sure, however, that they found the right star, it was
really necessary to compare their observations with a
good star map. If they found something which was not
on the star map, then this would be the new planet
which, of course, has no fixed position. Unfortunately
there was no such map at Cambridge.

In the meantime, Leverrier , had also communicated
with the observatory at Berlin, where a first-rate map
of the heavens had just been completed. The head of
this observatory pointed his telescope in the direction
advised by Leverrier, and with the aid of his map was
at once able to pick out the new planet, which was not
a mere point like the other stars, but appeared as a small
disc. The news of the discovery travelled quickly over
Europe, and England realised that she had lost the race.
If all concerned had been a little more alert, from John
Adams to the Astronomer Royal, or the professor at
Cambridge, the honour of the discovery might have been
theirs.

However, the world nowadays honours Mr Adams
for his real priority, though, as his papers had not been
published, he could not claim this officially. Luckily,
his was the character to take the disappointment in a
generous manner and so save one of those unseemly
disputes which, alas, have sometimes arisen in similar
circumstances !

ASTRONOMY 209

The new planet was called Neptune, and was found to
take third place among the others in size. It is quite
invisible to the naked eye, although Uranus may be seen
by any one with good sight knowing where to look.
Uranus takes eighty-four years to revolve round the sun,
while the time of one revolution by Neptune is one
hundred and sixty-four years, nearly twice as long.
When the path of Neptune was well established it was
found, as with Uranus, that there was a discrepancy
between this observed path and the one calculated.
Accordingly yet another planet was searched for by the
methods of Adams and Leverrier. In 1930 it was thought
that this planet had been located from the Mount Wilson
Observatory in America. Further investigations showed,
however, that though this new star, since named Pluto,
undoubtedly is a planet, it is not nearly large enough to
account for the deviation of Neptune from its calculated
path. The search must, therefore, still go on.

II

We must now go back in time and see how gradually
our knowledge of the heavens increased. This know-
ledge was not only of the positions of the various stars
but of the distances between us and them; of the rates
at and directions in which they move; and even of the
matter of which they are composed. Now, all the know-
ledge we have of the heavens comes to us in one way
only by means of light. If there were no light, or if we
could not perceive it, the heavens, as far as we are con-
cerned, might not exist. As our knowledge concerning
light itself advanced, therefore, so did our knowledge of
the sun and stars from which the light comes.

210 THE ROAD TO MODERN SCIENCE

The Speed of Light. One of the oldest problems con-
cerned the rate at which light travelled. It obviously
travelled exceedingly quickly, but did it really take time
to do so? The first man to attack the problem experi-
mentally was Galileo, who arranged men with lanterns
on opposite hills to signal backwards and forwards, each
showing his light immediately he saw the other's. As the
men grew practised in responding, the time diminished
until there was no reason to suppose there was an interval
at all. We now know that such an experiment carried out
on this earth is bound to fail, because the distances are too
small. Not unless the distance across which the light was
sent was very great indeed, or unless the means of flashing
the light and measuring the time were far more exact,
could the experiment have succeeded.

Olaus Roemer. It was a young Danish Astronomer,
Olaus Roemer, who saw how the speed of light might
be found by letting a star signal to the earth over the
great distance between. The star he used was one of
the moons of Jupiter which had first been seen by Galileo
through his telescope. 1 Periodically these moons, in
revolving round Jupiter, pass behind the latter into the
cone of shadow cast by the sun. We say there is an
eclipse of the particular moon under observation.

Now the moons move at constant speed, and there-
fore these eclipses should occur at regular intervals.
Roemer observed the eclipses carefully and found this
was not the case. At certain times the eclipses were
early and at others late, the variation being a maximum
of about eight minutes each way. Roemer came to the
conclusion that the explanation of this difference was

1 The word 'star' is used here in a general sense. Strictly
speaking, Jupiter 's moons are not stars, as they are not self-luminous.

ASTRONOMY 211

that light did take a definite time to travel. At certain
times of the year Jupiter and the earth are on the same
side of the sun, when an eclipse of one of Jupiter's moons
occurs. In this case, the light will have the shortest
distance to travel to the earth. The eclipse will, there-
fore, be seen to take place before the time calculated from

FIG. 37. Illustrating two eclipses of one of Jupiter's moons
(Mj and M 2 ). The earth is shown in two positions (Ei and E 2 )

the average of all the intervals. When the earth is right
away from Jupiter on the opposite side of the sun,
however, the light will have to travel much farther to
reach the earth. The extra distance will be that of the
diameter of the earth's orbit, which Roemer knew to
be approximately one hundred and eighty-six million
(186,000,000) miles. Since there was a difference of
sixteen minutes between the shortest and the longest
intervals between the observed eclipses he argued that

212 THE ROAD TO MODERN SCIENCE

it must take the light sixteen minutes (approximately
1000 seconds) to travel the one hundred and eighty-six
niillion miles across the earth's orbit. This would make
the speed of light one hundred and eighty-six thousand
miles per second. This is certainly a tremendous speed,
but it is what we call * finite,' not infinite that is, light
does not travel instantaneously.

During the last century a very beautiful experiment
to determine the velocity of light was carried out by a
Frenchman named Fizeau. This was comparable to
Galileo's experiment in that it was carried out on the
earth's surface and an artificial source of light was used.
By the nineteenth century, however, instruments had
been perfected to such an extent that it was possible to
carry out the whole experiment mechanically and to
measure absolutely accurately very short intervals of
time. The details of the experiment are too difficult to
follow here, but it is interesting to note that Fizeau con-
firmed Roemer's approximate value, at the same time
determining the velocity with much greater precision.
The figure, 186,000 miles, or 300,000 kilometres, per
second, is near enough for us to remember.

The Distances of the Stars. One of the earliest men
who attempted to measure the distances of the sun and
moon from the earth was Hipparchus of Nicea, a Greek
living in the second century B.C., about one hundred
years after Archimedes. By this time the science of
Geometry was well advanced, and Hipparchus was able
to bring this to his aid in making his calculations. The
only measurements which he made were of angles sub-
tended by these heavenly bodies from points on the
earth at different times of the year. In the hands of
the Arabs astronomical instruments were very greatly

ASTRONOMY 213

improved, and in the time of Galileo and Newton the
measurement of such distances as those of the diameter
of the earth's orbit, and the distance from the earth of
the moon, sun, and the planets, offered little difficulty.
We cannot here go into the method used ; but, if you are
interested and can get hold of Sir William Bragg's book
called The Universe of Light, you will find that, on p. 200,
he explains, as simply as is possible, how these measure-
ments are made.

Herschel attempted to apply these same methods in
finding the distances of the fixed stars, but he failed,
because the stars are so very much farther away from us
than the sun and the planets. In 1838 a German named
Bessel, with the aid of a very beautifully designed in-
strument called a heliometer, succeeded where Herschel
had failed. From thenceforward, knowledge concerning
the distances of the stars from the earth, and from each
other, gradually accumulated.

Compared with the kind of distances with which we
deal on this earth, the distance away of the sun is very
great. It is ninety-three million miles. The average
distance from the sun of the outermost planet, Neptune,
is two thousand eight hundred million miles. If these
distances are small compared with those of the fixed stars
from the earth, it is at once apparent that the latter must
be very great indeed. The nearest star to us is about
four hundred thousand times farther away than the sun.
Others are so far away that it is still impossible to measure
their distance. It is obvious that the mile, which is a
unit chosen for use on our pigmy earth, becomes absurdly
small when used to measure these distances. Accord-
ingly, astronomers have chosen a new unit. This is
the distance travelled by light in one year ; and this they

214 THE ROAD TO MODERN SCIENCE

call a 'light-year/ Since light travels one hundred and
eighty-six thousand miles per second, the distance it
travels in a year must be 186,000 x 60 x 60 x 24 x 365
miles. This comes to over five billion miles !

The nearest star is just over four light-years away.
This means that the light by which we see this star to-day
started on its journey to us four years ago, while light
from the farthest stars started centuries ago. Our news
of the heavens is, therefore, a trifle behind the times, but
it is the best we can get !

Ill

Spectrum Analysis

The Composition of the Sun and Stars. By investigating
the kind of light which comes from the sun or any par-
ticular star, we are now able to find out what chemical
elements are present in the matter of which it is com-
posed. To follow this process you must be quite sure
that you understand that a ray of light is really a train
of waves through the ether, and that the only difference
between different coloured lights is in the size of these
waves. You know that when white light is passed through
a prism a band of colours in a definite order is obtained,
called a spectrum. The wave-length of the light forming
a spectrum decreases regularly from the red end to the
violet end, and there is a definite wave-length correspond-
ing to each part of the spectrum. If this is well under-
stood, what comes next should follow quite easily.

Josef Fraunhofer (1787-1826). The splendid tele-
scope, called a heliometer, with which Bessel was first able
to measure distances among the fixed stars, was made for
him by a very clever young workman called Fraunhofer.

ASTRONOMY 215

This young man had been apprenticed to a mirror-maker
very early, since he was an orphan. While working for
this master the house collapsed and buried Fraunhofer
in the ruins, from which, fortunately, he was rescued alive.
His miraculous escape attracted the interest of the Prince
of Bavaria, and his poverty and ill-health so excited the
Prince's sympathy that the latter gave him a handsome
present of money. With this Fraunhofer bought his
freedom from his master and also bought books and learnt
engraving on metal. A few years later he entered some
large optical works and soon became famous for the in-
struments he made. His most important achievement
was a great improvement in the manufacture of glass,
which enabled far more precise results to be obtained with
lenses, mirrors, and prisms made of it.

Fraunhofer himself made a very important discovery
with a prism made of this improved glass. He was able
to get with it a very beautiful and clear spectrum, using
the sun's light. In this spectrum he found something
which Newton, with his inferior prism, had missed.
Instead of the colours being continuous from one end to
the other, he saw that the spectrum was crossed at intervals
by a number of dark lines. He observed these dark lines
on many different occasions, and every time he found that
the lines were in exactly the same places.

Next, he used the light coming from Venus to make a
spectrum, and again he found the dark lines. There were
also lines in the light from certain fixed stars, but these
were rather differently grouped. He made very careful
drawings of all these spectra and numbered and lettered
the lines. Forty-five years later, when two German
professors found out what was the cause of these lines,
Fraunhofer's careful records were a great help to them.

2i6 THE ROAD TO MODERN SCIENCE

Bunsen and Kirchoff. These two professors worked
at the University of Heidelberg. They also were in-
vestigating different kinds of spectra. Each of them
made a very important discovery, and the two discoveries
together explained the dark lines in the sun's spectrum
which now are always known as the Fraunhofer lines.

Bunsen discovered that when the vapour of a substance
is made to glow, the light from it, if passed through a
prism, does not show all the colours given by white light
but only certain coloured lines with dark spaces in
between. For instance, if the metal sodium is heated in
a flame, the flame gives out yellow light, which, on passing
through a prism, gives two narrow yellow lines, which are
always in the same place. Other elements give many more
lines of other colours, but the same element always gives
exactly the same lines, no matter with what else it is mixed.

Bunsen saw that this was a very good way of finding out
whether any element was present in a substance. All
that had to be done was to turn the substance into vapour
by holding it in a hot flame and look at the flame through
a prism, or rather a specially designed instrument con-
taining a prism, called a spectrometer. If the lines
characteristic of the element were seen, then that element
was known certainly to be contained in the substance. It
was to get a clean hot flame for vaporising substances
that Bunsen invented his famous * Bunsen burner/

These special spectra by which the elements can be
identified are only given by gases. Let us see what sort
of light is given out by hot solids and liquids. Suppose
an iron ball is gradually heated so that it begins to glow.
The colour, as you know, changes from a dull red to a
bright red, which gets more and more yellow until finally
the ball is white hot, If the rays coming from the ball

ASTRONOMY 217

are sent through a spectroscope, it can be shown that, at
first, they consist almost entirely of radiant heat waves.
These, you remember, are the next in size to waves of red
light. They cannot, of course, be seen with the eye, but
there are instruments which will detect them. As the
ball gets hotter, red light begins to appear, then orange
and yellow, and so on, right through the spectrum, until
all the colours are there. At this point the ball, when
looked at directly, appears white. The individual colours
can only be seen by separating them with a prism. Light
from intensely hot solids then gives a complete continuous
spectrum. It is not correct to say that the sun is exactly
solid; but the matter in the centre is so closely packed
together that the elements are not able to give out their
own individual spectra as they can in the rarefied gaseous
state. We can take it, therefore, that white light comes
from the interior of the sun.

Now we come to KirchofFs discovery. It will be best
explained by describing one of the experiments he did.
First of all he obtained a very bright source of white light
which gave a continuous spectrum with no dark bands
when passed through a prism. Then he placed, between
the light and the prism, a flame coloured yellow with
sodium, like the one Bunsen used. On examining the
spectrum now, he found that there were two black lines
in it in exactly the same position as the bright lines which
Bunsen had got when he used the sodium flame alone.
Let us now see what Kirchoff learnt from this.

Where the black lines were, obviously no light was
falling. There was light falling there before the sodium
flame was introduced, because the white light gave a con-
tinuous spectrum. The only explanation was that the
sodium flame had absorbed the light of those particular

2i8 THE ROAD TO MODERN SCIENCE

wave-lengths. But these were the waves which the
sodium flame by itself sent out. It would seem, there-
fore, that if white light falls on a glowing gas the elements
in that gas pick out and retain their own characteristic
kind of light, but let all the rest pass on. Kirchoff proved
that this was so by using many other elements besides
sodium. He always found that the kind of light which
was ordinarily sent out by the element was taken away
from the white light.

Perhaps you have seen by now how helpful that dis-
covery was in explaining Fraunhofer's lines in the spec-
trum of sunlight. As we have seen, the centre of the
sun gives out white light because it is very hot and very
dense. Round the outside, however, the atoms are not
nearly so closely squashed together, and are really in the
gaseous state. So we have white light coming to us
through the envelope of glowing vapour round the sun.
The elements in this vapour absorb their particular kinds
of light so that, when it reaches the earth and is passed
through a prism, Fraunhofer's black lines are seen.

Fraunhofer had measured the position of these lines
very carefully. Bunsen had found the positions of the
characteristic lines of nearly all the elements found on the
earth. Nearly all the black lines corresponded with
elements known on the earth, and so, in this way, the
material of which the sun is made was analysed into its
chemical elements. Remembering that the sun is ninety-
three million miles away, that was really something of an
achievement !

There was one element detected in the sun which was
not discovered on earth until some years afterwards.
That was the element Helium, whose name means 'the
sun/ You probably know that this is a light non-

ASTRONOMY 219

inflammable gas used in airships. So far, no element
has been discovered in the sun or in any of the stars
which is not known on earth. The whole universe is,
therefore, composed of just the same 'stuff.'

The Temperature of the Stars. We saw that as the
temperature of a solid, such as an iron ball, is raised it
begins to give out light of shorter and shorter wave-
lengths. It is possible, by examining the spectrum of
light given out by a star, to calculate its temperature.
This is done by seeing in which part of the spectrum the
light is most intense. The shorter the wave-length of the
most intense part the higher is the temperature of the star
from which the light is coming. If you look at the stars
on a clear night you will see that some seem to give a bluish
light, while others are definitely orange. The blue stars
are the hottest stars of all.

Motions of the Stars. It is also possible to tell from
the spectrum of a star whether it is approaching or re-
treating from the earth. I am not going to attempt to
tell you how this is done. A curious fact has been found
out, however, in this way. It seems probable that the
very far-off nebulae are all rushing outwards away from us
and from each other at a tremendous pace ; in fact, that
there is a general outward expanding movement of all
the stars and nebulae of the universe. We shall have a
little more to say about the universe in the last chapter
of all.

CHAPTER XV

Biology

i

The Scope of Biology. Biology is a word which has
only come into general use comparatively recently. It
means 'the study of living things/ and includes the
sciences known as Botany, the study of plants; Zoology,
the study of animals ; Physiology, the study of the human
body; and Psychology, the study of the human mind.
Psychology is the newest of all these branches and the
most difficult. We shall not have anything to say about
it here.

It has taken men much longer to learn about living
things than about the rest of the physical world. One
reason for this is that they have to take living things more
or less as they find them and cannot very easily stage
experiments to show just the one thing which they want
to know. In Physics it is generally possible to think out
an experiment in advance and arrange that nothing shall
interfere with the particular event that is being studied.
In dealing with living things, however, this is not possible.

Another reason is that man has embedded in him a
great reverence for life. So we find a reluctance to take
the life of animals, or to use the body of the dead in the
search after knowledge. Lately, however, this reluctance
has been overcome by the recognition that the welfare of
future generations is at stake.

Aristotle. The early study of life was almost always
connected with the study of medicine. Aristotle was

220

BIOLOGY 221

the first man we know of certainly who studied all kinds
of living creatures and wrote about them. His writings,
however, deal not only with what he discovered for him-
self, but also with what men long before him had found
out and written down in books of which there is now no
trace.

There are two ways of studying living things. In
Anatomy we deal with their structure. It is compara-
tively easy to study, as it can be carried on with creatures
after they are dead. They can be dissected and the
various parts examined. But to know all about the
parts and organs of a creature when it is dead is not to
know how those parts and organs function when the
creature is alive. This knowledge is sought for in the
study of Physiology, and is much more difficult to gain.

Galen (A.D. 130-200). The old doctors were, of
course, interested in the anatomy of the human body,
but it was not easy to study this. For a time, in Alex-
andria, the law allowed the bodies of criminals to be used
for the purpose, but, for the most part, such a thing was
rarely done. Instead, men dissected the corpses of the
higher animals, chiefly apes and dogs; and supposed
that human bodies were very similar. A certain Roman
doctor, named Galen, collected together all the know-
ledge of anatomy gained in this way by his predecessors,
and added many observations of his own. All this he
wrote down in a book.

The important thing to remember about Galen is that
his book became the great Authority for doctors in the
Middle Ages. I hope, by now, you have realised what
a tremendous part 'Authority' played in those times.
During the dark ages, as we saw, men gave up the study
of science altogether. When they again began to be

222 THE ROAD TO MODERN SCIENCE

interested it was to the old writings that they turned
and not to life itself. In the various universities that
sprang up all over Europe the students working for their
doctor's degree had to learn the books of Aristotle and
Galen wholesale, and never did any finding out for them-
selves. Later, some attempt at demonstration was made
at lectures, but the dissections were carried out by pro-
fessional 'barbers/ as they were called, who probably
did it so badly that it was quite impossible to see
whether or not their results agreed with the teachings
of Galen.

Vesalius (1514-1564). In 1514, five years before
Leonardo da Vinci died, there was born in Brussels a
man who was to change all this. His name was Vesalius.
He belonged to a cultured and learned family and many
of his ancestors had been physicians. Very early in life
he developed a passion for dissection, and, by practising
on birds, rabbits, dogs, and all sorts of small animals,
he soon acquired very great skill in it. He quite naturally
decided to be a doctor and went to Paris to study and
take his degree. From there he went to the University
of Padua, in Italy, to be in charge of the Department of
Anatomy. At first he did what everyone had always
done, and taught his students straight out of Galen's
book. He could not stand the clumsy work of the pro-
fessional barbers, however, and very soon he took to
doing his own dissections. This at once led to some
remarkable discoveries. Remember that he was now
dissecting human bodies, and that the writings of Galen,
although about the human body, were based on the study
of animals such as the ape and the dog. Galen said
that there were three bones to the lower jaw. Vesalius
only found one. Again, Galen said that the thigh bones

BIOLOGY 223

were curved, but Vesalius found that they were straight.
Many other such contradictions were brought to light
in this way, and in yet another instance the old pillar of
Authority began to crumble and fall. In many cases
the mistakes made by Galen were due to the fact that
animals had been dissected instead of humans ; but much
error was also caused because he had included in his book
all sorts of statements based on old superstitions and
beliefs. For example, it was an old belief that man was
a rib short on one side because woman was made from
one of man's ribs. Vesalius, however, soon showed that
there were just the same number each side !

These discoveries made a great stir in Padua. Not
only was Vesalius a very skilled dissector but he had
also a very lively and vigorous personality, and students
flocked to hear his lectures. In this way the new
generation of doctors learnt to dissect for themselves
and to discard the old teachings of Galen.

Vesalius himself now set to work to study the human
body very carefully, and at the end of five years published
a book on its anatomy. This he dedicated to the Emperor
Charles V. It was a most interesting book. Not only
did it contain a great deal of new knowledge based on
true observation, but it was also very beautifully illus-
trated with drawings of the structure of various parts
of the body. These illustrations were done by a pupil
of the famous Italian painter, Titian. If you have seen
any portraits painted about this period you will remember
that behind the figure there is always painted in an Italian
landscape. Exactly the same thing was done in the
illustrations to this book by Vesalius. Behind a great
figure dissected, say to show the muscles of the back of
the body, was to be seen a very beautiful landscape ! The

224 THE ROAD TO MODERN SCIENCE

whole book was remarkable both for its matter and for
its production. (See Plate XIX.)

Vesalius may have been popular in the University of
Padua, but the publication of his book soon made him
unpopular outside of it. It was the same old story. The
new discoveries trampled on the old and cherished beliefs,
and the book was pronounced to be blasphemous.
Vesalius was forced to leave Padua, but, luckily, was
appointed Court Physician to Charles V and, after the
latter's death, to Philip II of Spain. After nineteen
years in this capacity, however, through some cause not
certainly known, he fell from favour and had to leave
Spain. He went on a voyage to Palestine, and, on the
way home, his ship was wrecked. He was stranded on
one of the Ionian islands, and there died from exposure.
It is worth while to remember the name of Vesalius and
what he did. His book laid the foundation of all modern
biological science. He overthrew the old false god of
Authority and founded a new tradition in the study of
anatomy. He made errors, but these were soon corrected
by his successors working according to the methods he
had taught.

Meanwhile, there was still no certain knowledge about
physiology or the working of the body. The current
beliefs were, for the most part, those of Paracelsus who
envisaged a kind of presiding demon superintending the
various internal workings of the body. The first man
to attempt to investigate any of these processes by experi-
ment was an Englishman named William Harvey, who
established as a fact what is now termed the ' Circulation
of the Blood/

Harvey (1578-1667). William Harvey was born at
Folkestone in 1578, in the reign of Queen Elizabeth.

PLATE XIX

Illustration from Vesalius' book on Anatomy
(Drawn by a pupil of Titian)

BIOLOGY 225

As a boy he went to King's School, Canterbury, and
afterwards to Caius College, Cambridge. From Cam-
bridge he went to Padua and studied anatomy under a
very famous professor named Fabricius. Harvey came
to know Fabricius well, and was most interested in the
discoveries the latter was making about the little doors or
'valves ' in the veins. It was well known that there were
two kinds of blood-vessels leading from the heart. There
were the deep-seated arteries carrying very red blood
which spurted out when the artery was cut, and the veins
which were near the surface. At intervals the veins had
these valves, which Fabricius was studying, and contained
dark purple blood which oozed rather than spurted when
the vein was cut. The arteries and the veins did not
appear to meet anywhere in the body.

It was also known that the heart was divided into four
chambers, two on the right and two on the left. The
top chambers were called the auricles and the bottom
the ventricles. Look at the diagram to understand this.
There were quite clear openings from the auricles to the
corresponding ventricles, but no apparent passage from
one side of the heart to the other.

It was, of course, also well known that the heart and
the arteries appear to beat that is, the blood passes in
pulses. Galen had explained this by supposing that
there was a continual ebb and flow that is, a backwards
and forwards movement of the blood in both the arteries
and the veins to and from the heart. He said that the
dark blood in the veins was crude blood, while that in
the arteries was mixed with vital spirits which made it
bright and lively. He thought that there were tiny pores
in the wall dividing the heart vertically, and through these
pores some of the crude blood oozed from the right side

226 THE ROAD TO MODERN SCIENCE

to the left, where it became charged with vital spirits.
He also thought that some crude blood from the right

FIG. 38. Diagram of the circulation of the blood

(From The Discovery of the Circulation of the Blood, by permission of Dr Singer.)

side travelled through the lungs to the left side. He was
proved to be right in this last supposition.

The valves that Fabricius was investigating in the veins
were rather like trap-doors which will only open one way.
In this case they opened towards the heart. This fact
interested Harvey very much, for it showed him that the

BIOLOGY 227

idea of the blood pulsing backwards and forwards in the
veins was an impossible one. The blood could only
move one way, towards the heart. Some other explana-
tion of the movement of the blood must, therefore, be
found. With this problem in his mind he left Padua
and returned to England, where he soon became a very
prosperous doctor and later on physician to King
Charles I. At the same time he set about experimenting
to see whether an idea which he had had was the right
one. This was the idea.

Since the blood could only go towards the heart in the
veins it had to come from somewhere. Might it not be
that there really was some connection between the veins
and the arteries, and that the blood went out from the
heart through the arteries and back through the veins?
The only alternate explanation would be that new blood
was being made all the time. Harvey soon showed that
this was not the case. By experimenting with animals
he was able to show that the quantity of blood leaving
the left side of the heart through the arteries in half an
hour was more than the total amount of the blood in the
body at any one time. The only possible explanation
of this was that the blood was going round the body and
coming back again. There is something very important
to notice here. Harvey had begun to use measurement.
We have already seen that whenever men begin to measure
quantities in science then we get a sure and certain
advance.

Harvey did not rest with this as the only proof of his
theory. He next carried out experiments with what are
known as ligatures. First he bound up the top of some-
body's arm very tightly, so that both arteries and veins
were closed up and no blood could pass through. The

228 THE ROAD TO MODERN SCIENCE

pulse in the wrist stopped, and the hand became blue
and cold because there was no blood flowing through it.
Then he loosened the bandage a little and found that the
veins on the arm and hand below the bandage began to
swell and become knotted. This, he explained, was
because the loosened bandage no longer compressed the
arteries and blood flowed to the hand. The veins on the
surface, however, were still compressed, and so, below
the bandage, they became very full and swollen, as the
blood was continually being pumped into them from the
arteries and could not escape.

In this way Harvey showed that his idea had been right.
The blood leaves the heart by the arteries and returns to
it by the veins. He also showed that the heart itself is
the pump which keeps the blood moving. The muscles
round the heart contract and squeeze out the blood, then
they relax and the heart dilates and fills up again. He
further showed that Galen had been right in thinking
that the blood goes from the right side of the heart to
the left by way of the lungs, but quite wrong in saying
that some oozes through the division down the middle.
The arrows in the diagram will show you quite clearly
the path of the blood round the body. Harvey never
actually saw the blood passing from the arteries to the
veins through the tiny vessels which we call capillaries.
When microscopes came into use this was quite clearly
seen, as we shall hear.

In spite of the fact that he was physician to the un-
fortunate Charles I, Harvey died quite a wealthy and
prosperous man. He was with the King during the first
part of the Civil War, but he had no taste for war and was
glad to be persuaded by his brothers, who were wealthy
London business men, to leave the fighting and settle

BIOLOGY 229

down. They had, meanwhile, looked after his money
for him, and so he was quite comfortably off. When he
died, in 1667, he left his money to the College of Physicians
in London. There is a portrait of him there and also
one in the National Portrait Gallery.

Harvey's discovery of the circulation of the blood is the
only one in physiology which we can describe in detail.
After Priestley's discovery of oxygen and Lavoisier's
experiments on the part played by oxygen in the air, the
process of respiration was fully investigated. It was
found that the red colour of the blood in the arteries was
due to the oxygen which was absorbed as the blood
passed from the right to the left side of the heart through
the lungs. As the blood reaches the different parts of the
body it gradually loses this oxygen and becomes dark in
colour once again.

Miiller (1774-1842). As men's knowledge of chemistry
and physics increased, so this knowledge was gradually
applied to the understanding of various life processes.
The man most famous for his investigations in physiology
was a German professor named Johannes Miiller, who
lived from 1774-1842. In his laboratory at Berlin he
and his students carried out many experiments and in-
vented all sorts of apparatus for investigating the workings
of the human body ; and modern knowledge is based very
largely on their results.

II

Discoveries with the Microscope

Now we must go back to the years immediately follow-
ing Harvey's death and follow another path along which
progress was made. The telescope, in the hands of

2 3 o THE ROAD TO MODERN SCIENCE

Galileo, brought the vast solar system within man's ken.
The microscope was to open up yet another field of vision.
To whom should go the credit for the invention of the
microscope is not certainly known, but at about the same
time as the invention of the telescope it was found that
lenses could be made which would make tiny things
appear much larger. When these new microscopes were
turned on living things, discoveries immediately began to
be made. Three men stand out as making really im-
portant contributions to knowledge in this way. They
are:

Marcello Malpighi an Italian . 1628-1694

Jan Swammerdam a Dutchman . 1637-1680
Anthony van Leeuwenhoek also a

Dutchman .... 1632-1723.

Marcello Malpighi was the son of a small landowner.
He studied to be a doctor at the University of Bologna.
After qualifying, he held successive posts at a number of
the universities of northern Italy, and finally became
physician to Pope Innocent XII. With the new micro-
scope he examined all sorts of structures which hitherto,
in the study of anatomy, could only be imperfectly seen.
In this way he was able to examine the air-passages in
the lungs and the tiny blood-vessels which Harvey had
not been able to see for himself. He also saw the cor-
puscles in the blood which give it its colour; and the
separate layers of the skin.

One of his most interesting bits of work was the study
of the silkworm and the tracing of its life-history. With
his microscope he was able to see the nerves, air-passages,
and food canal in the insect, and to compare these parts
with those in the better-known and larger animals. He

BIOLOGY 231

was also able to see the mechanism whereby the silk-
worm forms the silk which makes it so valuable to man.

Lastly, he used his microscope to look below the
surface in plants and described and made drawings of
the structures which we now call cells.

Jan Swammerdam was born in Ley den. He was a
wealthy man, who qualified also as a doctor, but devoted
his time entirely to work with the microscope. His
especial interest was the study of insects, and he became
very clever at dissecting them under the microscope. If
you think for a moment what this means you will realise
that it requires a great deal of deftness and skill. In
addition, Swammerdam made very beautiful drawings of
what he saw. In this way he examined a number of
insects, especially bees and mayflies. He also studied
other small animals, such as snails and squids. Hitherto
nothing was known about the anatomy of these small
creatures, and our present knowledge of them is based
largely on Swammerdam's work. All this meant looking
through the microscope in a very bright light, which is a
great strain and very trying. Swammerdam worked so
hard and so incessantly that he completely wore himself
out over it and died when he was still quite a young man.

Anthony van Leeuwenhoek was quite a different type
of man from the other two we have heard about. He was
not educated at a university, and lacked entirely any
scientific training. Looking through the microscope
was really a hobby for him, so that he did not devote
himself to any one particular subject and try to find out
all he could in a methodical manner. Instead, he worked
in a very haphazard fashion, looking at any and everything
which suggested itself to him.

Little is known about his early life, except that he was

232 THE ROAD TO MODERN SCIENCE

born and lived at Delft in Holland. It is probable that he
kept some sort of a shop, but it is quite certain that, for
the latter part of his life, the shop took up little of his time.

Anthony van Leeuwenhoek not only used microscopes
but made them for himself. There were two kinds of
microscopes in use then; one sort had two lenses, one at
each end of a short tube. This kind was like our modern
microscope. The other consisted of only one very thick
lens which had to be placed very near the object to be
viewed. We now call such a lens a magnifying glass.
Leeuwenhoek not only ground his own lenses but also
made metal holders to contain the lens and fix the object
in the right position. These holders differed according
to what he wanted to look at. One sort was made to
clamp a test-tube firmly just in front of the lens, so that
liquids could be examined (Plate XX); and there were
many other kinds. For a long time the Royal Society in
London had a set of these microscopes which Leeuwen-
hoek had given them. Unfortunately, some time during
the eighteenth century these were borrowed and never
returned, and so a very valuable possession was lost.

As already stated, Leeuwenhoek examined a great
variety of things under the microscope. He wrote about
his discoveries in a very rambling and discursive manner.
One of the most interesting things to remember about him
is that he actually saw the tiny capillary blood-vessels
linking the arteries with the veins. Harvey knew that
these, or something like them, must exist, but, lacking the
microscope, he never saw them. Leeuwenhoek first saw
them in the thin transparent part of a tadpole's tail which
he had in a test-tube.

One day he put some pond water in a tube and looked
at it through his microscope. To the naked eye it was

BIOLOGY 233

just muddy water. To his amazement, however, on
looking through the lens he found that it was full of tiny
creatures moving up and down and all over the place.
They were not all alike; some were red and some were
green; some had forked tails which they lashed about;
others had horns on their heads, or long streamers with
which they churned the water; while still others looked
like discs of floating jelly. Here was a whole new un-
suspected world. These little creatures that Leeuwen-
hoek discovered are the simplest forms of living things.
We now call them Protozoa. Leeuwenhoek found that,
if the water dried up so that only the mud was left, these
little creatures also dried up ; but when water was again
added, even after a year or two, they all ' came to life
again,' and were as lively as before.

These are just two of the discoveries that Van Leeuwen-
hoek made with his microscope. He lived to a great age,
and saw more new things, perhaps, than any man of his
time. But he was not really such a good scientist as
either Malpighi or Swammerdam.

The Cell Theory. In the eighteenth and early nine-
teenth centuries the miscroscope was used more and
more to study the structure of plants and animals. It
was realised that different parts were made up of different
tissues, and these tissues were classified and called by
different names. Over and over again, however, the box-
like structures which Malpighi had first described were
seen to make up these tissues. They could be seen most
clearly in plants, and seemed to consist of transparent walls
containing, as a rule, a jelly-like substance. Later it was
discovered that in the middle of the cell was a denser part
of the jelly which was called the nucleus. Then cells were
seen also in animal tissues and the nucleus also recognised.

234 T HE ROAD TO MODERN SCIENCE

In 1839 a German scientist named Schwann y a pupil
of Johannes Miiller the physiologist, published a theory
about the structure of all living things which became
known as the Cell Theory. He said that he had come

FIG. 39. Surface view and section of a piece of onion
skin showing nuclei (N)

(From An Introduction to the Structure and Reproduction of Plants, by permission of
F. E. Fntsch, F.K.S., and E. J. Salisbury, F.R.S.)

to the conclusion that all living things, both plants and
animals, were made up entirely of cells, just as a house
is built of bricks or a chemical substance is built of atoms.
Schwann thought that the most important thing about
the cell was its wall, but in this he was proved to be
wrong. It was found that the cells in some animal
tissues have no walls at all ; and in 1861 another German,
Max Schultze, showed that the really important part of
the cell was the jelly-like material it contained with the
denser nucleus in the middle. This material he called
protoplasm, and it is the living material of both plants

BIOLOGY 235

and animals. The chemists were able to show that this
protoplasm contained definite chemical elements, but no
one had yet been able to manufacture it from those
elements. In it are bound up all the mysteries of life.
The dense region called the nucleus proved to be the
most important and interesting part of all, since in it are
known to be carried those characteristics which are in-
herited by one generation from the last.

How did this protoplasm come to be formed ? At one
time we know that there was no life on earth. Then one
day there was. How did it happen? That is still an
unanswered question. We do not know how the first
life appeared on earth, but we do now know how the
many forms of life which still appear to spring from
nowhere originate. It is the story of this discovery
which must now be told. It was a most important dis-
covery, for it has had very far-reaching and beneficial
effects on humanity.

It has long been known that if living matter, such as
meat, is allowed to decay, before long it will become alive
with maggots. Cheese or bread left about soon grows
upon itself a mould. The old explanation of this was that
life springs spontaneously from dirt, dust, and decaying
matter. Frogs and toads were supposed to come from
the mud of ponds, rats from the River Nile, and so on.

Redi. It was an Italian, Redi, who in 1668 first
thought of devising experiments to see if this view was,
after all, the correct one. He placed some meat in wide-
mouthed flasks; some of these he left open, others he
covered with paper, and still others with a very fine net.
The meat in all the flasks decayed and flies were attracted
by the smell. In the open flasks the usual crop of maggots
appeared, but not so in those covered with paper. In

236 THE ROAD TO MODERN SCIENCE

the case of the flasks covered with netting it was found
that the flies had laid eggs on the netting and these hatched
out into maggots. So the maggots had come from the
flies : life from life, not life from dirt.

Redi made other similar experiments, and finally came
to the conclusion that in all cases where life apparently
springs from dead matter, what has happened is that
germs of life have been introduced in some way from
without. In most cases these germs are too small to be
seen with the naked eye, although the flies' eggs could
have been seen if looked for. Leeuwenhoek saw some
of these germs, even smaller than the protozoa, in his
pond water; so small that even under the microscope
they looked just like tiny black specks.

The next advance was when scientists found out that
it was these germs or bacteria which cause organic matter
that is, matter which has been produced by living
organisms to decay. They also found that, if all air is
excluded, the material will keep fresh, because the germs
come from the air. That is, of course, the principle on
which all modern * tinned' foods keep fresh. The food
is generally heated to a definite temperature, to kill all
germs which might be in contact with it, and then sealed
down so that the tin is absolutely air-tight.

It is not very easy to be quite sure that all the germs
are killed, and all air excluded, and so it sometimes
happened that experiments made with food, in this way,
failed. That is to say, although it was thought all the
germs must have been killed, and no air allowed to get
to the food, yet the latter, in some cases, still went bad.
When this happened, the man who did the experiment
generally said that after all Redi and the others had been
wrong, and that life could spring out of nothing.

BIOLOGY 237

Louts Pasteur (1822-1895). The man who finally
settled the question once and for all was the famous
Louis Pasteur. Just over twenty-five years ago, a
popular French magazine arranged for its readers to
vote for the man whom they considered should take
first rank as a prominent Frenchman of the nineteenth
century. Fifteen million people voted altogether, and
Pasteur won most votes. He received a hundred
thousand more than the second on the list, who was
Victor Hugo, the popular writer. Since he was con-
sidered such a great man, we must go rather fully into
the story of his life and work.

Louis Pasteur was born in 1822 away in the east of
France, near the Jura mountains. His father was a tanner,
but had been a soldier in Napoleon's army. Pasteur
trained first as a crystallographer and chemist, but was
soon attracted to the study of biology. He became
especially interested in bacteria, as those tiny germs in
the air came to be called. His interest was first aroused
when a man named Pouchet carried out one of those
experiments with food which failed.

Pouchet filled a flask with boiling water, sealed it very
carefully, and then, turning it upside down, pushed the
neck under mercury. He then took out the cork. Next
he made some oxygen from chemicals and passed it
straight into the bottle so that some of the boiled water
was pushed out. Finally, with a pair of tongs, which
he heated strongly to kill any germs it might have on it,
he pushed into the bottle a little hay which had also been
' sterilised' by heating strongly. He then corked the
bottle again and put it aside. It now contained (a) pure
oxygen from chemicals, (b) boiled water, and (c) sterilised
hay. It could not possibly contain any bacteria or germs,

238 THE ROAD TO MODERN SCIENCE

said Pouchet. Nevertheless, in a few days the water
had become cloudy, and when examined under the
microscope was found to be swarming with bacteria.
Thereupon Pouchet proclaimed that the prevailing idea
that life, even of bacteria, must come from life (in other
words, that germs must have parents !) was wrong. Here,
these germs had originated quite spontaneously.

Pasteur was quite sure that Pouchet was wrong, and
that, in spite of all his precaution, somehow or other some
germs had got into the bottle. He repeated the experi-
ment himself very carefully and found out what had
happened. Then, in front of a large audience at the
Sorbonne, the famous University at Paris, he did the
experiment once again. This time, however, he had
the room darkened, and had directed on to his apparatus
a very brilliant beam of light. Then it could be seen
that the surface of the mercury, although it had looked
clean, was really covered with a layer of dust. Pasteur
showed that when a body was plunged under the mercury,
some of these dust particles were carried with it. So that,
when the hay was introduced into the bottle, some dust
got in too, and with the dust some bacteria.

That was the start of Pasteur's work. He then went
on to show that bacteria are floating everywhere in the
dust of the air. Catching some dust in gun-cotton, he
dissolved the latter away in ether, and examined the
residue under the microscope, finding always bacteria.
He also showed that in some places air contains far more
bacteria than others. For example, in a stuffy bedroom
he found very many germs, while in pure mountain air
hardly any at all. The experiment by which he showed
this is too long to describe here. That is an important
feature of Pasteur's work. All his experiments took a

BIOLOGY 239

long time and needed a great deal of care and patience.
There was nothing quick and spectacular about them.

Pasteur became famous chiefly because he used his
knowledge and talent in ways which were of lasting benefit
to other people. Soon after he began studying bacteria,
he met a man who made alcohol from beetroots. This
business was being ruined because the alcohol would not
keep but went bad. Alcohol can be made from a number
of things, but it is always made from something which
contains sugar, such as fruit, barley, or beetroot. The
process is known as fermentation and the liquid becomes
frothy in the process. Until Pasteur got to work on the
matter no one understood how it happened. They were
quite content so long as it did happen.

The first thing that Pasteur showed was that, whenever
fermentation occurs, living bacteria are always present.
When beer is made, the yeast which has to be added is
the source of the bacteria. Yeast is composed of thousands
of little globes, all stuck together, each of which is a tiny
plant-germ. With his microscope Pasteur was able to
see these bacteria in every case of fermentation.

The second thing he found was that, in the case of the
bad alcohol, a rod-shaped yeast was growing instead of
the proper round one. As long as even one of these
rods was left in the vat the new lot would go bad, since
the one rod-shaped plant was capable of producing
thousands more in a very short time. The only thing to
do was to scrap the vats and start afresh.

Pasteur realised that the souring of milk and the grow-
ing of the mould on cheese were the same sort of change,
and so he set to work to look for the plant or creature (for
bacteria can be animals or plants) which caused the
change. In each case he found it.

240 THE ROAD TO MODERN SCIENCE

The next piece of work he did was with silkworms.
A large part of the south of France depends for its liveli-
hood on the rearing of silkworms and the manufacture
of silk articles. It was a dreadful thing, therefore, when,
in 1865, a disease broke out amongst the silkworms and
they all began to die. Still worse, the new eggs hatched
out the next year produced silkworms with the same
disease.

Pasteur spent a long time trying to find out what
caused the disease and how it could be stopped. He
found, as he expected, that it was due to a 'germ,' and
he showed the farmers how to recognise which worms
carried the germ and warned them against using eggs
from those worms. He also told them not to let healthy
worms touch any leaves which had had the sick ones on
them in case any germs should be left there.

Robert Koch. Before going on to the most famous of
all Pasteur's discoveries we must stop for a moment to
hear about another man who was living at the same time
and working along the same lines as Pasteur. This man
was a German named Robert Koch. He is famous for
his discovery that all infectious diseases are due to germs
or microbes which can be passed from one person to
another. Before he died he had identified the germs
producing quite a number of serious diseases, notably,
perhaps, those of tuberculosis and of cholera. At the
time about which we are talking, however, it was a disease
called anthrax, attacking sheep and cows, in which he was
interested. This disease seemed to be infectious, but
people were not quite sure, as sometimes it seemed to
come from nowhere.

Koch found that mice could be made to take this
^disease, and so with these in his laboratory he set to

PLATE XX

PLATE XXI

V-i

PH
c/o

I

BIOLOGY 241

work to study it. One of the first things he did was to
look at their blood under the microscope. He found
that the blood of those mice which had anthrax contained
lots of little dark rods which made the blood look almost
black. As the animal got worse the rods began to grow
and stretch, forming a tangled mass of threads. He then
injected some of this blood into an animal that had not
got the disease and found that it soon developed all the
symptoms. So he showed that these rods were the germs
which carried the disease.

Pasteur heard of this work of Koch and was very much
interested in it. He then wondered whether a germ
could not be found which would kill the anthrax germs
and so cure the disease. So he also began experimenting
with mice. Then a chance arose of experimenting with
some cows which had the disease.

There was another man who claimed to be able to cure
the disease by rubbing the cow violently, cutting greal
gashes in her, and then smearing on some horrible oint-
ment. It was a case of the cure being worse than the
disease! Pasteur thought that if the cows got better
after that treatment they probably would have done sc
anyhow. However, together they tried an experiment.

Anthrax germs from a sick cow were injected into four
healthy cows. Each one soon developed the disease,
Then this other man, Louvrier, was allowed to treat twc
of them in his own fashion, and the other two were left
alone. One of the cows which Louvrier treated died
and one got better. One of the cows left alone died
and the other got better. After that Pasteur was quite
sure that Louvrier's treatment was no good.

Pasteur next thought he would see if these two cows
which recovered could catch the disease again. He

16

242 THE ROAD TO MODERN SCIENCE

therefore injected into each of them a large dose of an-
thrax germs. Nothing whatever happened to them ; they
remained quite well. So, thought Pasteur, if only the
cows could be made slightly ill with anthrax they would
afterwards be safe from bad attacks which might kill them.
He then went back to his laboratory to try to find out how
he could manage to bring this about.

Eventually he found that if the anthrax germs are kept
for some time in a bottle they become much weaker and
do not have nearly such a bad effect when injected into
animals. He therefore proposed that these weak germs
should be injected into all healthy cattle so that in future
farmers would be safe from this terrible plague which
killed so many of their animals. But, of course, there
were lots of people who said that it was a very dangerous
thing to do and wanted to stop Pasteur. Finally, a great
public trial was arranged.

About fifty animals were bought for the purpose and
divided into lots. Into one lot Pasteur injected his weak
germs or 'vaccines.' Then a little later he injected into
all of them strong and virulent anthrax germs. After
three days all the animals were publicly inspected. Not
one of all the animals which had been injected with the
weak germs first was the least bit ill. Of the others almost
all were dead and the rest dying. There could be
absolutely no doubt that Pasteur was right, and his fame
was assured.

Jenner (1749-1823). Pasteur's idea was not quite new.
Nearly a hundred years before an English doctor named
Jenner had done something very similar when he first
vaccinated people to prevent them getting smallpox.
There is a rather similar disease called cow-pox which
cows get and often pass on to the people who milk them.

BIOLOGY 243

It is, however, very much milder than smallpox itself and
people do not die of it. Now Jenner, after years of care-
ful study, came to the conclusion that anyone who had
had cow-pox was immune from smallpox that is, would
not catch smallpox however much he came in contact
with the disease. Jenner then tried putting some of the
pus, or matter, produced in the sores of people suffering
from cow-pox into small cuts made on the arm of a boy.
Sometime after this he did the same thing with pus from
a smallpox sore. In the first case a cow-pox sore was
formed; but the pus from the smallpox sore had no
effect. So Jenner found a way of protecting people from
smallpox. When you are vaccinated you are really
given a mild form of cow-pox which will prevent you
from catching smallpox if ever you come near to it.
Jenner, of course, knew nothing about germs as Pasteur
did.

Four years after his famous experiment with cattle
Pasteur found out how to prevent the development of
hydrophobia, that terrible illness which develops in people
bitten by mad dogs. This also was by innoculating them
with germs which would overcome those producing the
illness.

By this time Pasteur had shown how important the
study of bacteria was from the point of view of human
welfare. Accordingly there was built in Paris, with
money subscribed by people from every part of France,
the Pasteur Institute. Here every kind of disease was
studied with the object of finding out some scientific way
of controlling it. The result is that to-day almost every
disease, if taken in time, can be cured. I am sure you
will agree that not only France, but the whole world, owes
a great debt of gratitude to Louis Pasteur.

244 THE ROAD TO MODERN SCIENCE

Lister (1827-1912). There is one other man whose
name must be classed with those of Pasteur and Koch in
this triumphant battle against these tiny but powerful
organisms. This man was a Scotsman, Sir Joseph Lister,
afterwards Lord Lister. He was a surgeon in Glasgow
Infirmary at the time (1860-1870) when Pasteur first began
to publish the result of his experiments showing that the
air was full of these bacteria, the harbingers of decay and
disease.

At that time the surgical wards of a hospital were de-
pressing places. In spite of the skill which surgeons were
gaining in performing operations, their patients very
rarely got better. This was because the wounds made,
instead of healing cleanly and quickly, developed a horrible
disease called gangrene, which is a kind of blood-poison-
ing. The patient became very ill indeed and often died.
The same thing happened if it was an accident which
had caused the wound; if, for instance, a broken bone
pierced through the flesh and skin.

Lister was a very clever surgeon, and it grieved him to
feel that all his care and skill were of no avail. After
many years of watching and observation he came to the
conclusion that there was one kind of wound which never
developed this terrible gangrene, and which, if proper care
were taken, generally healed quickly without making the
patient very ill. This was a wound made inside the body
by, say, a broken rib piercing the lung. If, however, in
addition, the outside skin were pierced, then such a wound
developed gangrene like the others.

When Lister read about Pasteur's work and realised
what a lot of seeds of disease were floating in the air, he
knew what was the cause of the trouble. The wounds
made inside did not come in contact with the air. These

BIOLOGY 245

healed, because no germs of disease got to them to make
them putrefy. Wherever the air could penetrate, however,
there the germs would be also, and disease would follow in
their track.

Lister made up his mind that he must cover all the
wounds with something which would kill the germs and
prevent their working harm. First he soaked dressings
in carbolic acid and put them on the wound before he
bandaged it. Then he transformed his operating theatre
and his wards by banishing everything which would
harbour dirt and germs. Above all, he kept them
scrupulously clean. Instead of the dirty old garment
which surgeons used to wear every time they operated he
put on a clean white coat.

In a very short time success crowned his efforts. His
patients got well without developing any of the usual bad
diseases; while, in the next ward, which was not under
his care, the old suffering and misery went on.

It took a long time, nevertheless, to win over the other
surgeons to his method. This is known as the antiseptic
or 'the against-germ ' method. Nowadays it is the
aseptic method (i.e. without germs) that is used. The
disinfectants that kill the germs are also bad for the
wounds; so that, instead of killing the germs on the
wound, care is taken that no germs reach it at all. Every-
thing used in the operation is thoroughly cleansed and
disinfected, including the air in the room. As you
probably know, all the doctors and nurses wear light
washing clothes and the hair is covered up completely.
It is essential that everyone should do their job properly.
One careless nurse can ruin all the surgeon's work.

246 THE ROAD TO MODERN SCIENCE

III

The Relationship between the Various Forms of Life

So much for the war against germs. Up till now the
microscope has shown the way. Now we must go back
a little in time and take up the story of another path along
which biological knowledge advanced. In this story we
shall see how men tried to view all forms of life as a whole ;
to compare them and link them together, and finally to
find out how there came to be such variety among living
things.

Linnceus (1707-1778). The first thing to do in studying
a great number of things altogether is to classify them
that is, to arrange together in groups all those which are
alike in some chosen respect. Aristotle had done this as
far as he was able, but he dealt chiefly with animals. In
the eighteenth century a Swedish naturalist, named Karl
Linnaeus, made a very important classification of all living
things. First of all he divided them into two kingdoms,
the animal and vegetable. Then he divided each king-
dom into a number of ' phyla ' according to the broad plan
of their anatomy; for example, animals with backbones
(vertebrates) and animals without backbones (inverte-
brates). These Phyla he again divided into classes;
classes into orders; orders into families; families into
genera; and genera into species. Species is the name he
gave to individual kinds of things such as the brown rat,
the lion, the tiger, etc.; or the bulbous buttercup, the
lesser celandine, the common daisy, etc., among the
plants.

Two examples will serve to illustrate this classification.
As we have seen, one of the phyla into which the Animal
Kingdom is divided is the Vertebrata, comprising all

BIOLOGY

animals with a backbone. In this Phylum is the Class
Mammalia, which includes all mammals, i.e. animals which
do not lay eggs but bring forth their young alive and
suckle them. The Order Carnivora contains all flesh-
eating mammals. The Cat-tribe (Felidae) is a Family of
this order ; and in it we find the Genus Felis which com-
prises the Species Felis domesticus (domestic cat), Felis leo
(lion), Felis tigris (tiger), and so on.

In the Vegetable Kingdom, the common buttercup
(Ranunculus arvensis) is a Species of the Genus Ranunculus
of the Family Ranunculaceae of the Order Dicotyledons, 1
of the Class Angiosperma, 2 of the Phylum Spermatophyta. 3

Animal Kingdom Vegetable Kingdom

Vertebrata (phylum) Spermatophyta

Mammalia (class) Angiosperma

I I

Carnivora (order) Dictoyledons

Felidae (family) Ranunculaceae

i i

Felis (genus) Ranunculus

i i

Felis domesticus (species) Ranunculus

arvensis

All this tidying up was very useful; but, as so often
happens, people got so interested in giving things their
proper label that they lost interest in the things themselves.
The Linnaean system of classification is used in much the
same form to-day.

Cuvier (1769-1832). The next man who figures in
this story was a Frenchman, Georges Cuvier. He was
born in 1769 and died in 1832, so that he lived through

1 Dicotyledons = Plants bearing two rudimentary leaves in embryo.

2 Angiosperma = Plants bearing seeds in closed ovaries,
8 Spermatophyta = Plants bearing seeds

248 THE ROAD TO MODERN SCIENCE

stirring times. During the Reign of Terror in the French
Revolution he was acting as tutor to the sons of a wealthy
man and lived for some years on the coast of Normandy,
away from all the excitement in Paris. While there he had
plenty of time and opportunity to follow his interest in
Natural History and became acquainted with several of
the leading naturalists of the time. Later he went to
Paris to be in charge of the Jardin des Plantes or
Botanical Gardens and finally became famous as a friend
of Napoleon, who gave him a high office of state.

Although, originally, Cuvier's interest lay with plants it
was with animals that he did his most valuable work.
He studied all the different kinds of animals he possibly
could and compared their different parts. For example,
he compared the organs with which such different animals
as man, a horse, a fish, a spider, an insect, etc., breathed
or digested their food. Again he compared the nervous
systems of all these animals and so on. He realised that
to be able to understand the simple types of animals
would be a great help in studying the more elaborate
processes in the higher types.

Cuvier divided animals into four classes only :

(1) The vertebrates, or the animals furnished with
backbones. These include mammals, birds, reptiles,
and fishes.

(2) Molluscs which include all the shell-fish.

(3) The articulated or jointed animals, such as crabs,
lobsters, spiders, and insects.

(4) The radiated type, such as starfish.

Near Paris a rock named Gypsum is to be found from
which the famous Plaster of Paris is made. At the
beginning of the nineteenth century workmen digging in

BIOLOGY 249

these rocks found a great number of bones and fossilised
remains of animals, some of them of gigantic size.

Fossils had been found and known for many centuries,
but various opinions had been held as to what they really
were. A fossil is a bit of rock or stone having the shape
or the impression of a part of a plant or an animal. (See
Plate XX.) Fossilised ferns can sometimes be quite clearly
seen on a piece of coal. The cliffs in many parts of Eng-
land often contain the fossils of shells; chalk-pits are
usually full of them.

All sorts of queer superstitions were at first held about
fossils. The first man to realise that they were the
remains of animals and plants which had formerly been
alive and had become hardened with time was Leonardo
da Vinci. By the time of Cuvier this was universally
recognised, but there was still a great deal of discussion
as to how they got there. The favourite explanation was
that they were the remains of animals that had perished in
the great flood at the time of Noah.

When all these new fossils were unearthed near Paris,
Cuvier at once set to work to examine them. Remember
that he had spent years studying the anatomy of every
kind of animal, so that he was especially fitted to under-
take this work. Many of the bones he identified easily,
but a number, he found, did not belong to any animal which
was then known, although they were very like those of
elephants in some respects. This was interesting,
because it showed that there used to be animals on the
earth which are no longer to be found there.

His interest once turned in this direction, Cuvier spent
the next twenty-five years examining fossils from all parts
of the world. Gradually he came to the conclusion that,
from time to time, certain types of animals died and new

250 THE ROAD TO MODERN SCIENCE

ones were formed. The older kinds were, of course,
always to be found buried deeper in the earth. Now
Cuvier was a firm believer in the theory that the animals
whose remains were found as fossils had been buried in
the earth at the time of a great flood. His new dis-
coveries, however, forced him to the conclusion that
there must have been a series of floods catastrophes he
called them. He stuck firmly to this opinion all his
life.

Lamarck (1744-1829). Side by side with Cuvier there
was working in Paris another scientist, considerably less
honoured and deferred to than Cuvier by his contem-
poraries, but who is now judged to be by far the greater
man of the two. This was Jean Baptiste Lamarck. It
was largely through his efforts that Cuvier gained his
appointment at the Jardin des Plantes. In later years,
however, Cuvier, the favoured of Napoleon, did not treat
Lamarck with the kindness and respect which he owed to
him.

Lamarck was also interested in the fossils, but, while
Cuvier devoted himself mainly to those of the vertebrate
or backboned animals, Lamarck studied the invertebrates
with great care. His investigations led him to con-
clusions which differed from those of Cuvier. He found
that, although many forms of animal life disappeared and
others took their place, there were no definite times at
which these disappearances took place. While some
forms disappeared, others lived on. There was, in fact,
to be found a gradual succession of forms of life.

William Smith. Meanwhile, an English surveyor was
making discoveries which confirmed Lamarck in the
conclusion to which he was gradually coming. William
Smith was engaged in the work of building canals up and

BIOLOGY

251

down the country. This meant, of course, a good deal
of digging and excavating. He was of a very observant
type of mind, and his attention was soon attracted by
certain regularities to be found. The earth through
which he cut was arranged in definite strata or layers of
rock which always appeared in a definite order. In these
strata fossils were often to be found embedded, but
and this was the interesting point the fossils found were

FIG. 40. Showing the strata beneath London

characteristic of the particular stratum. For example,
there was a certain fossil of an extinct snail-like shell
animal called the ammonite. There were also three
layers of clay in the strata through which he dug; one
on top, which is called London clay; one just underneath
the chalk, called the gault clay; and one much lower,
called the Oxford clay. In the London clay no fossil
ammonites have ever been found, but there are a great
many fossil fruits of palms and conifers. In the gault
clay there are no fossil plant fruits, but ammonites of an
irregular spiral shape are to be found. Finally, in the
Oxford clay, there are huge numbers of perfectly regular
ammonites.

252 THE ROAD TO MODERN SCIENCE

In some places William Smith found that the top layers
had been worn away, exposing lower layers, but once he
had studied the layers carefully where they came in the
right order he was always able to recognise any particular
layer by the fossils which it contained.

All this strengthened Lamarck in his belief that there
had not been a series of sudden changes in the forms
of life inhabiting the earth brought about by sudden
cataclysms such as floods. Instead, he felt sure that the
changes had been slow and gradual and that one species
had 'evolved' from another. This theory of simpler
animals gradually changing and giving rise to more
elaborate species in the course of long periods of time
is known as the Theory of Evolution. It was not quite
a new idea. Certain Greeks had thought of it. There
are not very many ideas which the Greeks did not think
of first, but here again the new thing was the evidence on
which the theory was based.

Lamarck probably did not think of all the various forms
of life as starting from one very simple form, such as the
protozoa, as we do now. He thought that the changes
just took place within certain groups. His explanation
of how the change took place was a very ingenious one.
For example, he said, suppose a certain antelope found
he could reach up and eat the leaves of trees. Liking
this food he would continue to stretch up, with the result
that his neck would grow gradually a little longer. The
young of this antelope would be born with necks rather
longer than usual, and would stretch them still more by
eating leaves off trees. Their young would have still
longer necks, and so on, until finally we come to the
giraffes of to-day. Do you see the idea? Lamarck
thought of a good many other examples of the way

BIOLOGY 253

animals might alter themselves by constant use of a
certain part. We shall come back to this explanation
of Lamarck's later. In the meantime we shall see
how the evidence for the fact of evolution gradually
accumulated. You must realise that knowing for certain
that a thing has happened is by no means the same as
knowing how it happened. There has been a good deal
of confusion over this in the case of evolution, and people
who do not know much about it are inclined to think
that because we are not yet certain as to how evolution
occurred we do not know for certain that it has occurred.
This is quite wrong. We cannot possibly go further
into it here, but there is no doubt at all that man and all
the higher animals have evolved from the very simplest
forms of life. The change has been very gradual, but
we now know just what forms of life were present on the
earth at any particular time, and also how long it took
for these changes to occur.

Charles Lyell (1797-1875). The man who was re-
sponsible for a great deal of our knowledge about the age
of the earth and the story of life upon it was Charles Lyell,
a very famous British geologist. Geology is a branch of
science which we have not, so far, mentioned. It con-
cerns the study of the earth itself. Lyell realised that
the changes which have taken place in the earth in the
past can only be understood by studying the changes
which are going on at the present time. These are the
changes to which he paid special attention :

(1) Rivers are continually cutting channels through
rocks. In so doing they bring down the material worn
away as sediment which is deposited at their mouths,
often forming deltas.

(2) Rocks are also worn down by frost, wind, and

254 THE ROAD TO MODERN SCIENCE

wave, and the fine sand so formed is distributed by

wind.

(3) Animals die
and are covered up
by the material dis-
tributed, as shown
above.

.
Bird's

tt ov/irinq
jjfants

'"kfammafs

Trees

Seecfjyfanfs

Insects

Lancfpfanfs

TisfL

OLIGOCEKE

JUTUfsSK?

TJUjffSlC

CARBONIFEROUS

In this way succes-
sive layers are built up
in which dead animals
become embedded. The
soft parts decay, and the
harder shell is filled up
by sediment. As the
thickness of the layer
above increases, the
pressure hardens the
underneath layers, so
that the fossils are
formed.

Lyell calculated the
rate at which the layers
were being formed at
the present time, and so
was able to determine,

r .... ,

from its thickness, the
period of time occupied
in formingsome definite

Stratum. In this Way
t 11 f fi

ne Was aDle tO . nx
definite periods of time

during which certain forms of life existed on earth.
The diagram will give you some idea of what has

$00 >

last 500 million years. More primitive

forms existed for very many millions of

years before this

BIOLOGY 255

happened in past ages. No doubt many questions will
occur to you, but you must go to a book on Geology
for your answer.

Charles Darwin (1809-1882). The name which is
always connected with the Theory of Evolution is that of
Charles Darwin. This is because he devoted many years
of study to the subject, and finally wrote a book in which
the evidence put forward was so conclusive that a very
large number of people were convinced. Darwin did
not claim the idea to be new. What was new was his
explanation as to how evolution occurred.

First let us see how Darwin came to study the subject
at all. As a boy he lived in a village near Shrewsbury,
where his father was a doctor. He and his brother were
true country boys, and took a lively interest in all the
country life about them. Charles went to Cambridge
as a young man, but could not decide what he wanted
to do after that. Then he heard of a ship called the
Beagle, which was to go off on a five-years* voyage to
southern seas to make new charts. The captain of the
ship thought that there ought to be a naturalist on board
who would be able to examine and write about all the
animal and plant life in the seas and lands which they
visited. The Government did not agree with him, and
would not pay for one, but said that, if he could find any
one who would go for nothing, it had no objection.

Darwin thought what a splendid thing it would be to
go with the Beagle as its naturalist. He had learnt a lot
of natural history at Cambridge, and knew about the new
ideas concerning the earth and the possibility of evolu-
tion. His father did not want him to go ; but his uncle,
Josiah Wedgewood, backed him up, and in the end he
went.

256 THE ROAD TO MODERN SCIENCE

It was a wonderful experience. They went down the
east coast of America, up the Amazon and back, round
Cape Horn and up the Pacific coast. Finally they
crossed the Pacific and came back home by Australia
and New Zealand. Altogether, they were away five
years.

During the whole time Darwin examined and, when-
ever possible, collected specimens of every conceivable
kind of plant and creature, and a great number of fossils.
When he got home it took him years and years to go
through all his specimens. He wrote an account of his
voyage in a very interesting book called A Naturalist's
Voyage in H.M.S. Beagle.

There is not space here to go into all the evidence that
Darwin collected. The chief point was that it was quite
impossible to fix on a definite number of distinct species.
One kind gradually merged into another by infinitesimal
steps. Darwin, at the end of twenty years, published
all the evidence in his famous book The Origin of Species.
In this he also gave his explanation of how evolution
had come about. It was not the same as that of Lamarck.

He first of all pointed out that of all the tremendous
number of young creatures born only a very small
proportion survive. This is most strikingly true among
the lower forms of life.

He then suggested, what is also undoubtedly true, that
the ones that do survive are the ones that are most fitted
to cope with the surrounding circumstances. In other
words, the weakest go to the wall. This theory he called
that of the 'Survival of the Fittest/

In any given species the individual members are not
all identical. For example, some animals can run away
from their enemies faster than others of the same kind.

PLATE XXII

, TA - Elliott &> Fry

Charles Darwin

BIOLOGY 257

Those that can run fastest will live; the others will be
killed.

Then, Darwin said, the young of fast-running sur-
vivors will tend, on the whole, to run a little faster than
the average of the preceding generation. In this way
the species gradually changes by natural selection of the
fittest, and becomes faster moving. Probably the ability
to run fast was due to some slight difference in the forma-
tion of the legs or feet, and the new species produced
would all tend to have this character. If they had not,
they probably would not be able to run so fast, and so
would be killed.

At the present time scientists find it rather hard to
make either Lamarck's or Darwin's explanation fit the
facts completely; and they have not yet agreed upon
the true explanation as to how evolution occurred. They
all agree, however, that it has occurred.

Lamarck's explanation as to how evolution occurs is
usually known as the 'Inheritance of Acquired Char-
acteristics.' An individual is supposed to alter some
part by use, and this 'acquired characteristic' is then
inherited by the offspring. Darwin's explanation is
known as 'Natural Selection by the Survival of the
Fittest.' Scientists to-day cannot agree as to whether
these 'acquired characteristics' can be inherited by the
offspring of parents who acquire them. The evidence
is chiefly against it. On the other hand, the small differ-
ences which Darwin suggested are inherited and bring
about evolution, are now generally considered to be too
small to bring about a change in the time actually taken.
Until more is learnt about inheritance, the question must
remain unsettled, for it is on this point that scientists do
not agree.

258 THE ROAD TO MODERN SCIENCE

IV
Heredity

It is only quite recently that anything has been known
certainly about how inheritance functions. You have only
to look at a family to see, quite definitely, that certain
characteristics of the parents are inherited by the children.
Yet the children often have other characteristics pos-
sessed by neither of the parents.

By the nineteenth century it was known that in the higher
animals and plants a new living organism was always
produced in a definite way. In all species there were
two kinds the male and the female. These produced
certain characteristic cells differing from all the other
cells of which the organism was composed. These were
called gametes. In a flowering plant the male gametes
are the pollen grains, and the female gametes are the
ovules. In both plants and animals the male gamete is
small and easily detached from the parent; but the
female gamete remains attached to it. To produce a
new organism, a male gamete has to reach a female
gamete and join with it. From the cell formed by the
fusion of these two gametes the new organism grows.

The difficult question for scientists to decide was as to
how all the characteristics of the parent could be passed
on to the offspring by means of the one small cell.
Darwin supposed that minute particles from all parts
of the body collected in the gamete so that all parts made
their contribution. This was only an idea. He had no
proof.

Gregor Mendel (1822-1889). During Darwin's lifetime
an Austrian monk, Gregor Mendel, was carrying out
some very important experiments with ordinary garden

BIOLOGY 259

peas, which he grew in the monastery garden. When he
published these results no one took any notice of them
and he was very much disappointed. In 1900, however,
somebody came across his papers, and realised how very
important they were, so that now the name of Mendel is
very famous.

The merit in Mendel's work lies in the fact that, in
examining inherited characteristics, he only bothered
about one definite character at a time. For example, he
worked with two kinds of garden peas, a tall kind about
6 feet high, and a short kind only about i foot.

First of all he made sure that if pollen from a tall plant
was made to * fertilise/ that is, join with an ovule of another
tall plant, all the seeds produced grew into tall plants
without exception. Similarly, a short plant fertilised by
another short plant always gave short plants.

Then he took pollen from a tall pea and fertilised the
ovules of a short pea, tying the flower of the latter up in
muslin so that no pollen except what he put there himself
could reach it. He also took pollen from a short pea and
fertilised a tall one.

He then planted out the seeds produced in these two
ways. They all grew into tall peas as tall as the tall
parents, not half as tall, as might be expected. The
shortness of the one parent had apparently disappeared
altogether.

Next he fertilised each of these second generation tall
plants with their own pollen. This is called self- fertilis-
ing. The resulting third generation of peas was most
interesting. A quarter of the resulting plants were short
and three-quarters were tall The character of shortness
had not been lost after all, only hidden.

In the fourth generation, produced again by self-

260 THE ROAD TO MODERN SCIENCE

fertilisation, he found that all offspring of the short third
generation peas were short and no tall peas were obtained
from these so long as they were self-fertilised. Of the
tall plants of the third generation, one-third of them
produced tall plants only. The remaining two-thirds
produced three tall and one short out of every four, just
like the second generation.

We will put these results into a diagram :

Tall Peas Short Peas

All Tall Peas

Tall Peas Tall Peas Tall Peas Short Peas

Ail Tall Peas 3 Tall i Short 3 Tall i Short All Short Peas

Now let us see how Mendel explained this. He said
nearly all inherited characters go in pairs, such as tall-
ness and shortness, whiteness or colour, smoothness or
wrinkles, and so on. Those are characters of peas, but
he thought pairs could be found for nearly everything.

Each gamete produced by the parent carried something
which gives rise to one of these characters. But each
gamete could only carry one of these alternative pairs,
never both. This means that, since the original tall peas
always produced in all succeeding generations tall peas
when self-fertilised, then every gamete carried the
character of tallness. Similarly, all the gametes of the
short peas carried the factor of shortness.

Now, when the gametes of these two kinds of peas
joined together, the new cell produced in each case (called
the Zygote) must contain both characters. Why then

BIOLOGY 261

were the plants produced only tall ones? Mendel
supposed that the character of tallness must be stronger
in effect than that of shortness. He said it was the
dominant character, while shortness was a recessive char-
acter. Mendel did not know what it was in the gamete
which gave rise to the characteristic, so he called the
something 'a factor.' The second generation plants
contained both the factor for tallness and that for short-
ness, but, because the factor for tallness was dominant,
they were all tall.

When this second generation of peas produced gametes,
each gamete could only carry one of the factors, so that, of
all the gametes produced by any one plant, half would
carry the factor for tallness and half for shortness. Now,
when these gametes join together by self-fertilisation to
produce new zygotes there are three possibilities :

1. Two 'tall' gametes may join together.

2. Two * short* gametes may join together.

3. A 'tall' and a 'short* may join.

In the first case the new plants must be tall; in the
second they must be short ; while in the third they will be
tall because, although the * short ' factor is present, the tall
dominates it.

A diagram will make this quite clear (Fig. 42, p. 262).

Out of every four plants in the third generation, there-
fore, there ought to be three tall and one short, which is
what Mendel found.

During this century a great deal more work has been
done on the inheritance of certain characteristics and
Mendel's ideas have had to be altered a little to meet new
facts. Nevertheless, the debt owed to him is very great,
for he laid the foundation of all the work of this kind.

262 THE ROAD TO MODERN SCIENCE

This work is not only important from a purely scientific
point of view, but from a much wider social one. What
are now known as ' Mendelian ' characters have been
worked out for the human race in many cases, and it has
been found that many bad characteristics, such as certain
physical defects, are ' recessive ' characters like the short-
ness in peas. This means that they can be hidden in one

eft *v7//t TafC'Tacfor

O Gamef* v/iffc S&orf'facfor

Ttmafa. Gantefts

3 4

w

^

' v

n ,

(^

... n

Taff

Taff

tiorh

FIG. 42

generation but crop up in the next if they happen to be
hidden in both parents.

It would obviously be a good thing if bad characteristics
which weaken the human race could be cut out, but the
whole matter is, of course, extremely complicated. The
biologists of the day are hard at work on these and other
problems concerning the health of the community.

CHAPTER XVI

The Modern Road

IN Part I of this book we followed the early road-makers
as they blazed out the first trails which gradually widened
and straightened till, by the work of Galileo and Newton,
the great highway of Science was built on firm founda-
tions. In Part II we have seen how the highway was
divided into separate tracks each carrying its own traffic.
What of the road which is still being made ?

Three regions are occupying the attention of our
greatest scientists to-day. These are :

(1) the realm of the extremely small, which is to be
found inside the atom;

(2) the realm of the immensely large, of the great
universe about us ;

(3) and finally, that mysterious complex world of
Life itself.

The work to be done on the road into each of these
regions is still pioneer work. The country has to be
prospected as the road is built, and the ingenuity of the
road-builder is often taxed to the utmost to overcome the
obstacles in the way.

Quite a fair stretch of each road, however, has already
been made, and the workers on the road are becoming
familiar with the country. For us, however, it is not quite
so easy to follow them, and we must be content here with
a very brief account of some of their most important

discoveries.

263

264 THE ROAD TO MODERN SCIENCE

First, let us explore, with them, the inside of the atom.

During the greater part of the nineteenth century,
Dalton's picture of hard unbreakable atoms, like billiard-
balls, had been kept by all chemists and had served their
purpose very well. Since the end of the century, however,
one discovery after another has shown that this picture
was by no means a true one. I am not going to try to tell
you how these discoveries were made, but shall just give
you a general idea of what sort of a picture we hold to-day
of the inside of an atom.

To begin with, an atom is very far from being solid, like
a billiard-ball. The greater part of an atom, like the
greater part of the universe, is empty space. Secondly,
apart from this empty space, the atom is made up chiefly
of electric charges.

In the very centre of the atom is the part of it which
gives it its weight, called the nucleus. This nucleus bears
a positive charge of electricity. Circling round the out-
side of the nucleus, in much the same way as the planets
circle round the sun, are a number of negative charges of
electricity. These negative charges are called electrons ;
while the weighty positive charges making up the nucleus
are called protons. Since an ordinary atom is neutral
that is, it is not * electrified' the charge carried by the
electrons outside must always equal the charge on the
nucleus.

In the solar system the general rule is that only one planet
follows the same path round the sun. In the atom, on the
other hand, we may find as many as thirty-two electrons in
a ring. The outside ring, however, has never more than
eight. The lightest atom known is the Hydrogen atom.
This has one positive charge on its nucleus and one
electron circling round it. Helium, the next lightest

THE MODERN ROAD 265

substance, has two electrons outside, both following the
same path. Next in order of weight comes a rather rare
metal called Lithium, which has three electrons outside the
nucleus of its atom, two revolving on an inner ring and
one on an outer. Taking the elements in the order of
their atomic weight, each of the next seven atoms adds an
electron to the outer ring until there are eight altogether.
Then another ring is started; and so on.

-0 ++

FIG. 43. Atoms of various elements

As you know, negative and positive charges attract each
other; while charges of the same kind repel each other.
The inside of an atom is, therefore, full of these forces,
but as a rule the charges are so arranged that the forces in
different directions just balance each other, and the atom
like the solar system is stable. As the charges pile
up, however, a point is at last reached where the strain
becomes too great and some of the atoms break down
under it. The atom of lead has eighty-two electrons
circling round, and a positive charge of eighty-two on
the nucleus ; and Bismuth, another metal, has eighty-three
electrons. These are the two heaviest atoms which are
stable. There are several elements known which have
heavier atoms, but in every case we find the strain on the
nucleus has reached its limit. If we take a lump of any
one of these elements we know that, in a fair proportion
of the atoms making up the lump, the nucleus is exploding
and throwing out bits of itself, only settling down quietly

266 THE ROAD TO MODERN SCIENCE

when it has reached the size of the nucleus of the atom of
lead.

The substances with disrupting nuclei are known as
radio-active substances. The best known of them all is
Radium, which was discovered by M. and Mme Curie in
1898. It was mixed with the first radio-active substance
to be discovered, Uranium. The story of the discovery
of Radium is a famous one, and the reason for its fame is
twofold. First, Mme Curie was almost the only woman
to win a place of first rank amongst the discoverers in pure
Science. Her husband was killed in a street accident ten
years after the discovery, but Mme Curie lived on until
1934, and devoted her life to scientific work. Secondly,
the result of their labours, the element Radium, has
proved to be of great service to man in the hands of
doctors for the alleviation of human suffering.

The investigation of radio-active substances showed
that the disrupting atoms were shooting out three different
kinds of rays, known as the Alpha, Beta, and Gamma rays.
The Alpha rays consist of very swiftly moving particles
carrying a positive charge. Actually these Alpha par-
ticles consist of four protons (positively charged particles)
in a lump. The Beta rays consist of a stream of electrons
which have been embodied in the nucleus. Finally, the
Gamma rays have been found not to consist of particles
at all, but to be very rapid vibrations of the ether, or
waves of very short wave-length. They are, in fact, very
short, or 'hard' X-rays, but are more usually known as
Becquerel rays, after the man who discovered them.

These are the rays which are used in our hospitals to
try to cure the dreaded disease of cancer by killing the
growth which causes it. The rays, however, are not
discriminating in the tissues which they destroy, and

THE MODERN ROAD 267

so have to be used with the greatest caution. The best
thing which will really shut them off, by absorbing them,
is a thickness of several inches of lead. They pass
through other materials just as light passes through glass.
Accordingly Radium is always kept shielded by lead.
The actual dose to be used is in a lead 'needle/ and a
bunch of these needles is kept surrounded by blocks of
lead several inches thick, locked up in a safe. Every one
working with Radium wears rubber gloves, and, through-
out, the greatest care is exercised. Nowadays bad burns
only come from carelessness in its use ; but the early
workers, not understanding the substance with which
they had to deal, suffered badly.

It was the discovery of what was happening to the
atoms of radio-active substances which first gave scientists
any knowledge of what the inside of the nucleus was
like. As we have said, Becquerel was the name of the
man who first investigated a radio-active element, and
the substance which he investigated was Uranium, the
heaviest element of all. Then M. and Mme Curie
discovered, mixed with Uranium, the far more active
element Radium. This, as a matter of fact, is formed
from Uranium after it has shot off some of its nucleus, as
alpha and beta rays. Radium itself is, of course, not
stable, and its atoms also begin to break up, although
any one atom may remain a Radium atom for as long as
a thousand years. In a lump of Radium, however, there
are always some atoms breaking up and shooting out
rays.

The investigation of the rays and the transformations
of Uranium and Radium as they break up was carried
out chiefly by Professor Soddy and his helpers at Oxford.
Electrons had previously been discovered in quite

268 THE ROAD TO MODERN SCIENCE

another way by Professor J. J. Thomson at Cambridge.
Here there is a very famous laboratory known as the
Cavendish Laboratory. The money for this laboratory
was given by one of the descendants of the family to
which the great scientist Cavendish belonged, and is
one of the greatest * research * laboratories in the world.
The chief purpose of the workers in the Cavendish
laboratory during the last thirty or forty years has been
to find out all they can about the inside of the atom.
The leader in the work has been Dr Ernest Rutherford,
who has now been made Lord Rutherford in recognition
of his achievements.

The picture I have given you of the inside of an atom
was made by Lord Rutherford. As a matter of fact,
although it fits chemical ideas and facts very well indeed,
workers in Physics are not quite so pleased with it and
are looking for a slightly different one. This picture,
however, is the easiest one for us to understand, and so
long as we do not think we know the last word on the
matter it will serve us very well until the scientists can
give us another one which they are surer about.

Let us now consider what is the modern explanation
of what happens when things become electrified. Such
a state is most easily produced, you will remember,
by rubbing two things, such as wool and sealing-wax,
together. The sealing-wax then acquires a negative
charge and the wool an equal positive charge. To begin
with, all the atoms composing both wool and sealing-
wax are quite whole ; that is to say, they have their full
number of electrons revolving round a positively charged
nucleus. In the rubbing, however, some of the outer
electrons of the atoms composing the wool get rubbed
off on to the surface of the sealing-wax which, therefore,

THE MODERN ROAD 269

quite obviously has then a negative charge. Since some
of the atoms in the wool have lost electrons, the nuclei
of these atoms will have a greater positive charge than
the negative electrons left. The wool, as a whole, will
therefore be positively charged.

The important thing to remember about these new
ideas is, that only the electrons or negative charges can
move about from one part of a body to another. The
positive charges are firmly locked up in the centres of the
atoms. If, however, electrons leave one part of a body,
that part of the body will become positively charged.
All we have learnt about positive and negative charges
still holds so long as we remember that when we say a
positive charge moves in a certain direction, what is
really happening is that a negative charge (or a stream
of electrons) is moving in the opposite direction.

Since the electrons are on the outside of the atom, it
proved a comparatively easy matter to knock them off
and find out how they are arranged. It was much harder
to get at the nucleus. Quite recently, however, Lord
Rutherford and his helpers have succeeded here. They
have done this by shooting at the nucleus ! In Ruther-
ford's first experiment the missiles were those very
swiftly moving alpha rays, which, by the way, are really
atoms of helium without their attendant electrons. A
stream of these rays was sent into the gas nitrogen and
a kind of photograph taken of what happened. Just
one or two of these particles happened to hit the nucleus
of one of the nitrogen atoms. Experiments of the same
sort using other gases and other bombarding particles
have been carried out, and quite literally bits have been
knocked off the nucleus in some cases. The nucleus
left would, of course, be different, and so really what

2 7 o THE ROAD TO MODERN SCIENCE

they have done is to change one kind of atom into another!
A short time ago Lord Rutherford gave a lecture which
he entitled 'The Transmutation of Matter/ After all,
modern scientists are doing what the old alchemists tried
to do, though with somewhat different aims !

In the section on Astronomy we travelled some way
along the modern road which explores the universe and
there is not a great deal to add. One thing follows
directly on what we have just learnt about the inside of
an atom. The interiors of the hot stars and of the sun
are very, very dense, although they are not solid. They
are not solid because the molecules are vibrating far too
quickly to exist in the solid state. Because they are so
dense, however, there is not room for all the electrons
in their proper circles with all the space between. These
have got squeezed out, and the nuclei of the atoms are
all very near together. This at any rate is what our
modern scientists think. Sir Arthur Eddington, one of
Britain's foremost astronomers, has written a fascinating
book called Stars and Atoms y which is very well worth
reading, and gives a splendid picture of the Universe as
it is known by astronomers to-day.

The name of Einstein is one which is very often on
the lips of the scientific leaders of to-day. Why is this ?
It is because Einstein has proved himself to be one of the
giants among scientific men. Formerly Newton has
been almost universally acclaimed as foremost among
these giants. Now, undoubtedly, Einstein takes a place
at his side.

To explain to you what Einstein has done is, I fear, a
hopeless task. Even among people who have had some
special scientific training there are comparatively few

THE MODERN ROAD 271

who can follow him easily. His is a mathematical
achievement, and except to mathematicians the way
after him is barred. We can, nevertheless, perhaps get
some small idea of what the results of his work
mean.

To begin with, he showed that Newton's laws of motion
and of gravitation (which we explained fairly fully in the
first part of this book) did not explain everything as
completely as was thought. In ordinary everyday life
3n this earth Newton's laws hold very well, and machines
and experiments planned with them as a basis all work
perfectly well. But in the much vaster world of the
universe, or in the tiny world inside the atom, these laws
break down. Einstein, however, has supplied us with
others; or rather, so corrected Newton's laws, that they
hold, so far at any rate, in all three worlds.

We hear curious statements about Einstein's discoveries
and a good deal about the fourth dimension,' which is
Time. He certainly has shown that we keep space and
time too separate in our minds and that really they are
only part or dimensions of the one ' Space-Time ' of which
the universe is composed. We have got so used to
thinking of volume as the limit following length and area,
that to go one further and multiply by time to get Space-
Time makes our brains reel ! Luckily modern mathe-
maticians have very agile brains, and are able to move,
quite at home, in this new country.

One interesting thing Einstein has told us about our
universe of Space-Time is that it is not infinite, stretching
on endlessly, but is quite definitely limited. The correct
expression is that it is 'finite.' If you could set out on a
journey through the universe apparently in a straight
line you would eventually come back to your starting-

272 THE ROAD TO MODERN SCIENCE

point. In fact the universe is, in four dimensions, what
the sphere is in three and the circle in two.

Strangest of all, Einstein now tells us that all matter
is just a crinkle or a lump in this Space-Time universe.
Stars, such as our sun, are big crinkles, planets smaller
ones, and so on; the bigger the mass the bigger the
crinkle. But it is all very difficult and seems rather far
away from the roads we travel every day.

In the third realm, the realm of Life, the road seems
rather nearer to us. In fact, it is all-important that it
shall eventually be the everyday road along which man-
kind travels. For undoubtedly this, of all the roads
which science has carved out, seems to be the one which
is going to lead to the goal towards which men, since
they first appeared on earth, have been struggling. They
have not known, and still do not know, quite what that
goal is.

One fact has recently emerged as the result of modern
research, which is that a knowledge of the biological laws
governing human life is all-important in the efforts which
are made to ameliorate social conditions. Otherwise it
may happen that an apparent improvement in the con-
ditions of life of one generation may only make matters
worse for the next.

In the section on Biology I have indicated the lines
along which modern biologists are working. Three are
especially important. The first is the study of heredity,
by which we hope to be able to understand and control
what we, in this generation, pass on to those who
follow.

Secondly comes the study of the working of the human
body, and the influence on it of the food we eat and the

THE MODERN ROAD 273

conditions in which we live. The importance of this
work is obvious.

Finally, there is the study of the working of the human
mind. This undoubtedly will prove a very important
bit of the road. But it requires very special training, and
the making of this road will be very slow.

18

SUMMARIES OF PART II

SUMMARY TO CHAPTER X
I

The Hon. Robert Boyle (1627-1692)

'The Founder of Modern Chemistry/ Author of The
Sceptical Chymist. He defined the term ' Element/ He
urged' that the first object of all chemists should be to
search for the elements.

The Phlogiston Theory

All inflammable substances contain Phlogiston. When
these substances burn, phlogiston escapes. No in-
flammable substance can, therefore, be an element, except
pure phlogiston.

Dr Joseph Black (1728-1799)

He carried out the quantitative investigation of chalk,
magnesia alba, and the mild alkalis. He discovered that
each of these contained a gas which he called 'Fixed
Air,' now known as Carbon Dioxide.

Chalk = Quick-lime + Fixed Air.

Mild Alkali = Caustic Alkali + Fixed Air.

The Hon. Henry Cavendish (1731-1810)

(a) He realised the importance of measurement in
Science. By weighing equal volumes of the gases, he
showed that * inflammable air' (hydrogen) and 'fixed air*
(carbon dioxide) were totally different from each other
and from common air.

(b) He showed that water was not an element but a com-
pound of inflammable air (hydrogen) and dephlogisticated
air (oxygen).

Dr Joseph Priestley (1733-1804)

(a) He invented the pneumatic trough for collecting gases
or ' airs' which he obtained by heating various substances.

274

SUMMARIES 275

(b) His most famous discovery was that of oxygen which
he called Dephlogisticated Air. He obtained this by
heating Red Mercury Calx.

(c) He also collected and described Ammonia, Hydrogen
Chloride, and the Oxides of Nitrogen.

II
Jean Antoine Lavoisier (1743-1794)

(a) He overthrew the Phlogiston Theory and 'gave in its
stead the modern theory of Combustion.

By experiment he showed that air consists of two parts ;

an active part, oxygen, and an inactive part, nitrogen (or

azote).

When any substance burns in air, it combines with the

oxygen. The calx produced is, therefore, never an

element, while the inflammable substance may be.

(b) He drew up a list of substances which he considered
to be elements.

(c) He introduced a systematic scheme of names for
chemical substances which is still in use.

Karl Wilhelm Scheele (1742-1786)

(a) He discovered oxygen independently of Priestley, and
two years earlier

(b) He discovered Chlorine.

(c) He isolated a number of 'vegetable* acids.

Sir Humphry Davy (1778-1829)

(a) He invented the safety lamp to prevent explosions in
mines from the naked candle-flame.

(b) He established the fact that Chlorine was an element.
Since the well-known acid, hydrochloric acid, contains
only hydrogen and chlorine, he thus showed Lavoisier to
be mistaken in his 'oxygen-theory' of acids.

(c) Although not actually the discoverer of Iodine, he
was one of the first to investigate it, and classified it as
an element. He pointed out its similarity to chlorine,

276 THE ROAD TO MODERN SCIENCE

and predicted the discovery of another similar element,

Fluorine.

(d) By means of the electric current he decomposed the

caustic alkalis, quick-lime, baryta, and magnesia. In

this way he discovered the new metals sodium, potassium,

calcium, and magnesium.

Ill

Chemical Theory

The Law of Conservation of] rp, . , r , j

jyj These were established

rp, V r r^ * * r> f before the Atomic
1 he Law of Constant Fro- rp, , ,

portions. ) Theory was advanced.

John Dalton (1766-1844)

(a) In 1808 Dalton published his famous Atomic Theory
explaining chemical behaviour. All the chemical laws
can be deduced from this theory and confirmed by
experiment.

(b) He defined atoms and compound atoms (molecules)
and atomic and molecular weights. During the next
sixty years the majority of chemists devoted their
energies to the determination of atomic and molecular
weights. This finally led to a complete scheme of
classification of the elements based on their atomic
weights.

Organic Chemistry

(1) It was found that the majority of organic substances
contain the elements carbon, hydrogen, and oxygen.

(2) 1828. Wohler * synthesised ' urea.

(3) The molecules of organic compounds were found to
be extremely complicated, but always contained a
* skeleton* of carbon atoms.

(4) Methods were devised for changing the atom or
groups of atoms attached to a carbon atom of the skeleton.
This made possible the synthesis of a very great number
of organic compounds.

SUMMARIES 277

SUMMARY TO CHAPTER XI

I
Thales

The earliest of the Greek Philosophers. He investigated
the properties of amber and of the magnetic stone.

The Mariners 9 Compass

This first began to be used in the eleventh century.

Peter Peregrinus

He first defined the Poles of a Lodestone.

Dr William Gilbert (1544-1603)

He was the true founder of the sciences of Magnetism
and Electricity.

(a) He thoroughly investigated the properties of a magnet.

(b) He showed that the Earth was itself a huge magnet.

(c) He produced electricity by friction and distinguished
between electrics and non-electrics.

II
Dufay (1699-1739)

He recognised that there were two kinds of electricity,
vitreous and resinous. He found that like kinds repel
each other, but unlike kinds attract each other.

The Ley den Jar

This was invented by a Dutch professor to store elec-
tricity. Electric sparks could be drawn easily from such
a jar, which also produced a severe shock when dis-
charged through a human body.

Electrical Machines

Various types were invented during the eighteenth
century.

278 THE ROAD TO MODERN SCIENCE

Eenjamn Franklin (1706-1790)

(a) He suggested the theory that there was only one
kind of electricity. Positively charged (vitreous) bodies
have an excess, and negatively charged (resinous) bodies
have a deficiency of electricity.

(b) He showed that lightning was an electrical discharge,
either between two thunder-clouds, or between a thunder-
cloud and the earth.

The Hon. Henry Cavendish (1731-1810)

(a) He began to measure electrical quantities.

(b) He defined * electrical capacity* and 'degree of
electrification ' (electrical potential).

(c) He made condensers.

(d) He determined the conducting power of various
substances.

Ill
Luigi Galvani (1737-1789)

He discovered what he called 'animal electricity.' This
was discharged when two different metals in contact
were joined by a frog.

Alessandro Volta (1745-1827)

(a) He maintained that so-called animal electricity was
generated by the two different metals in contact. He
substituted other non-living moist conductors for the
frog and obtained a discharge.

(b) He constructed the famous ' Voltaic Pile * which gave
the first continuous current.

(c) He made the first simple cell.

Hans Christian Oersted (1777-1851)

He discovered that a magnetic field is produced around a
wire carrying a current of electricity.

SUMMARIES 279

Andre Marie Amptre (1775-1836)

He showed mathematically how to calculate the strength
of an electric current from the magnetic field which it
produced, (i) Galvanometers, and (2) the Electric
Telegraph are the direct itsult of Ampere's work.

George Simon Ohm (1789-1854)

He defined Electromotive Force (E. M. F.) and Resistance,
p

Ohm's Law: ^*=R.

Vx

IV

Michael Faraday (1791-1867)

(a) He explained the attraction and repulsion of magnetic
poles and electric charges by supposing the existence of
lines of magnetic and electric force.

(b) He discovered Electro-magnetic Induction, i.e. a
change in the strength of the magnetic field round a
conductor produces a current in the latter while the
change is taking place.

Some practical applications of this are :

(1) The dynamo.

(2) The electric motor.

(3) The telephone.

(c) He investigated the chemical action of the electric
current. These experiments led eventually to:

(1) the realisation of the electrical nature of chemical
action; and

(2) to the industry of electro-plating.

James Clerk Maxwell (1831-1879)

(a) He produced mathematical evidence in support of
Faraday's discoveries.

(b) He showed that light was 'electromagnetic' in nature.

(c) He predicted the discovery of wireless waves.

28o THE ROAD TO MODERN SCIENCE

SUMMARY TO CHAPTER XII

I

The Ancient World

Human and animal power alone were used to lift and
transport all loads.

Archimedes (287-212 B.C.)

He first constructed machines, in the shape of pulleys
and levers, as an aid to human power.

Leonardo da Vinci (1452-1519)

His notebooks are full of drawings of mechanical
devices.

Evangelista Torricelli (1608-1647)

(a) He first explained satisfactorily the working of a
suction-pump.

(b) He constructed the first barometer by which he
demonstrated and measured the pressure of the atmo-
sphere.

Blaise Pascal (1623-1662)

He planned, and his brother-in-law, Perrier, carried out,
an experiment which confirmed Torricelli *s opinion as
to the tremendous pressure of the atmosphere. This
experiment showed the possibility of measuring heights
by use of the barometer.

Jtto von Guericke (1602-1686)

(a) After many efforts, he succeeded in obtaining a
vacuum.

(b) He invented the first air-pump.

(c) He demonstrated in a spectacular fashion the tre-
mendous pressure of the atmosphere.

SUMMARIES 281

II

The Steam-Engine

Dionysius Papin (1647-1712)

He designed the steam-engine, but was never able to
obtain a satisfactory working model. The engine
worked under the power of atmospheric pressure.

Thomas Newcomen

He was an English iron worker who carried out Papin's
plans, and in 1711 constructed the first working steam-
engine, which was used to pump water out of mines. It
was very expensive to work, on account of the amount of
fuel consumed.

James Watt (1736-1819)

By fitting Newcomen's engine with a condenser he
reduced the necessary amount of fuel and so made the
steam-engine a practical proposition. It could now be
used for a variety of purposes.

Watt's Mow-pressure' engine has now been superseded
by the * high-pressure ' engine.

Ill
The Internal Combustion Engine

1. The first of these engines used coal gas and air as fuel.

2. The first successful petrol-engine was constructed by
Gottlieb Daimler. His engines were fitted to boats and then
to carriages, thus ushering in the age of the motor-car.

3. Count Zeppelin in 1900 constructed the first airship to
which a petrol-engine was fitted.

4. Wilbur and Orville Wright were the pioneers in aeroplane
construction. In 1903 they made a machine, fitted with a
petrol-engine, which flew 260 yards,

282 THE ROAD TO MODERN SCIENCE
SUMMARY TO CHAPTER XIII

Heat
Nature of Heat

The old conception of heat was of a weightless, invisible
fluid of definite substance. Lavoisier called it Caloric
and placed it in his list of elements.

Effects of Heat

(1) Chemical.

(2) Expansion.

Galileo used (2) in making the first thermometer.

Latent Heat

(1) This was first recognised by Dr Joseph Black as
the heat which disappears when a solid melts or a liquid
boils.

(2) Black also devised a method for measuring latent
heat, which is still used.

Units of Heat

The modern units of heat are :

(1) The Calorie, which is the amount of heat required to
raise the temperature of i grm. of water through i C.

(2) The British Thermal Unit (B.T.U.), which is the
amount of heat required to raise the temperature of
i Ib. of water through i F.

(3) The Therm, which is equal to 100,000 B.T.U.

Heat Capacity

Different substances require different amounts of heat
to raise their temperature by the same amount. Water
has the greatest heat capacity of all.

SUMMARIES 283

Heat a Form of Motion

(1) Count Rumford succeeded in boiling water by the
heat produced by friction when boring a brass cannon
with blunt tools.

(2) Sir Humphry Davy melted wax by rubbing two bits
together, although the temperature of the surroundings
was kept below the melting-point of ice.

In both (i) and (2) the only thing supplied externally
was motion. Both Rumford and Davy, therefore, con-
cluded that heat was a form of motion.

(3) Julius Robert Mayer (1814-1878) realised that other
forms of energy could be transformed into heat. He
showed that the difference between the work put into
a machine and that taken out appeared as heat caused by
the friction of the parts of the machine.

(4) James Prescott Joule (1818-1889) first determined
the Mechanical Equivalent of Heat. He devised a great
number of ways to do this.

The Principle of Conservation of Energy

This states that no Energy is ever lost or created. If it
apparently disappears in one form it will simultaneously
reappear in another. This principle was established by
the work of Mayer and Joule.

II

Sound
The Greeks

They knew that sound was caused by vibration and that
air was necessary for its transmission. Pythagoras
founded the science of music.

Leonardo da Vinci (1452-1519)

(1) Sound travels in waves through the air.

(2) An echo is caused by the reflection of sound waves
from a hard, smooth surface.

284 THE ROAD TO MODERN SCIENCE

Sir Isaac Newton (1643-1727)

(1) He investigated and described wave motion fully.

(2) He showed how to calculate the velocity of sound in
air when the density, temperature, pressure, and humidity
of air were known.

Ill

Light

Properties of Light known in Newton's Time

(1) It travelled in straight lines.

(2) The Law of Reflection was known.

(3) The Law of Refraction was known (Snell).

(4) The velocity of light had been determined by Roemer.

(5) White light could be decomposed into seven colours
by passing through a prism (Newton).

Isaac Newton

He upheld the Emission or Corpuscular Theory of Light.

(1) Light consists of streams of tiny fast-moving particles.

(2) These travel in straight lines.

(3) They are reflected from surfaces according to the law
of reflection.

(4) They travel at different speeds in different media, and
the path is, therefore, bent (Refraction).

Christian Huyghens (1629-1695)

(1) He objected to the Emission Theory on the grounds
that the particles in two streams of light which met would
collide. In practice they were known not to interfere
with each other.

(2) As an alternative, he advanced the ' Wave Theory of
Light/ According to this, light travelled in waves in
the same way as sound. Since it was known to pass
across a vacuum, he supposed the existence of the
ether which could vibrate.

SUMMARIES 285

Newton objected to the Wave Theory, because, if true,
light should spread slightly round corners. Thus
shadows from a point source should have blurred edges.
They apparently did not.

N.B. Owing to the authority of Newton in the world
of scientists, the Emission Theory was held universally
until the beginning of the nineteenth century.

Thomas Young (1773-1829)

He studied carefully both theories of light and devised
an experiment to decide between them.
This experiment decided in favour of Huyghens' Wave
Theory. Owing to the opposition of Lord Brougham,
little notice was taken of his work.

Augustine Fresnel (1788-1827)

(1) He obtained the same result as Young twelve years
later, and quite independently. He added mathematical
proof to the experimental one. On the publication of
his work, the Wave Theory was universally accepted.

(2) He showed that light vibrations are transverse and
not longitudinal.

IV

The Spectrum
The Corpuscular Theory

explained the different colours of the spectrum by
supposing a difference in size in the particles. Red rays
contained the largest particles and violet the smallest.

The Wave Theory

supposed a difference in wave-length between the rays of
different colours. Violet light has the shortest wave-
length and red the largest.

Radiant Heat (1800)

Sir William Her schel (1738-1822) discovered the existence
of Radiant Heat Waves (or Infra Red Rays) beyond the
red end of the spectrum.

286 THE ROAD TO MODERN SCIENCE

Ultra-violet Rays (1801)

These were next discovered beyond the violet end of the
spectrum. These are absorbed by ordinary glass.

X-Rays (1895)

These were discovered by Professor Rontgen. They
consist of waves of very short wave-length indeed. The
shortest X-rays often known as Becquerel rays are
given off from all radio-active substances.

Wireless Waves (1887-1901)

The possibility of these was predicted by Clerk Maxwell.
They were first produced by Heinrich Hertz in 1887 and
put to practical use by Marconi in 1901. Wireless waves
are the longest waves known. The wave-length varies
from about i centimetre to 2000 metres.

SUMMARY TO CHAPTER XIV

Sir William Herschel (1738-1822)

(a) He became expert at constructing very large powerful
reflecting telescopes.

(b) During his lifetime he carried out four detailed and
systematic surveys of the heavens. In this way he
discovered variable and double stars and many nebulae,
(r) In 1781 he discovered a new planet which was named
Uranus.

(d) He further discovered that the stars were not fixed
but were moving, often at great speeds.

(e) Finally, he arrived at the conclusion that the sun
was by no means the centre of the universe nor the
largest heavenly body.

Pierre Simon Laplace (1749-1827)

(d) By applying the Law of Gravitation he was able to
determine the effect of the planets on each other. In this

SUMMARIES 287

way he was able to account for a discrepancy between
certain calculations of Newton's as to the positions of
planets in the past and the records of actual observations
of these positions.

(b) He showed that the solar system was in equilibrium.

(c) He put forward his ' Nebular Hypothesis * to account
for the formation of the Solar System. This is not the
explanation given to-day.

John Adams (1819-1892) and Jean Joseph Leverrier (181 1-1877)

From the deviations of Uranus from the path calculated
according to the Law of Gravity, these two men in-
dependently calculated the position of a seventh, as yet
unknown, planet which was causing these deviations.
The new planet was found in the calculated place and
was called Neptune.

II

The Velocity of Light :
Olaus Roemer (1644-1710)

From observations of the eclipses of one of Jupiter's
moons he calculated the velocity of Light and found it to
be approximately 186,000 miles per second.

Armand Hippolyte Louis Fizeau (1819-1896)

In the nineteenth century, with very sensitive apparatus,
he confirmed Roemer's figure for the velocity of light.
His source of light was artificial and his distances com-
paratively small.

The Distances of the Stars :

Hipparchus of Nicea (Second Century B.C.)

This Greek astronomer was the first to attempt to
measure the distance of the sun and moon from the
earth.

288 THE ROAD TO MODERN SCIENCE

The Arabians

Their astrologers greatly improved astronomical instru-
ments so that these distances were more easily and
accurately measured.

Sir William Herschel

He tried to apply the old methods in finding the distances
of the fixed stars, but failed.

Frederick Wilhelm Bessel (1784-1846)

In 1838, using a heliometer, he succeeded where Herschel
had failed. The distances of the stars from the earth
and from each other are very great indeed. The unit of
measurement for these distances is the light-year.

Ill

Spectrum Analysis

The Composition of the Sun and Stars:
Josef Fraunhofer (1787-1826)

(a) He was a very famous instrument-maker.

(b) He brought about a great improvement in the
manufacture of glass used for prisms, mirrors, and lenses
in these optical instruments.

(c) With one of his new prisms he obtained a spectrum
from the sun's light which was crossed with dark lines.
He found similar lines in the spectrum from Venus and
from certain fixed stars. He made careful drawings of
the positions of these lines.

Robert Wilhelm Bunsen (1811-1899)

(a) He showed that elements in the glowing gaseous
state give Mine spectra/

(b) He examined and mapped the spectra of a great
number of elements.

SUMMARIES 289

Gustav Kirchoff (1824-1887)

(a) He found that, if white light is passed through hot
gases or vapours, the particular kind of light emitted by
the gas alone is now absorbed. Thus, if a spectrum
of the white light is obtained after it has passed through
the vapour, it is crossed by dark lines. These correspond
in position to the line spectrum of the gas.

(b) He found that the dark lines in the sun corresponded
to elements whose line spectra had been mapped by
Bunsen. He was thus able to identify elements present
in the vapour of the sun.

Examination of the spectrum of light from a star also
gives information concerning:

(1) its temperature,

(2) its motion towards or away from the earth.

SUMMARY TO CHAPTER XV

I

Aristotle

(a) He studied for himself many kinds of living things.

(b) He wrote down in his book many of the writings of
earlier men concerning plants and animals.

Galen (A.D. 130-200)

(a) He was a Roman doctor who collected together in a
book all the knowledge of his time concerning human
anatomy. This knowledge was gained from the study of
apes and dogs rather than humans.

(b) His book became the great ' Authority ' for the doctors
of the Middle Ages,

290 THE ROAD TO MODERN SCIENCE

Anatomy :

Vesalius (1514-1564)

(a) He was an Italian Professor of Anatomy who, contrary
to custom, carried out the dissections of the human body
to illustrate his lectures.

(b) In this way he discovered that many of the teachings
of Galen were false, being founded on the study of apes
and dogs instead of humans.

(c) He published a book on the Anatomy of the Human
Body, which laid the foundation of modern anatomy.

Physiology :

William Harvey (1578-1667)

He carried out the first experiments in Physiology by
establishing the fact of the Circulation of the Blood
He showed :

(a) that the blood could only flow one way in the veins,
because of the valves ;

(b) by measuring the quantity of blood leaving the heart
in a given time, that it circulates round the body and
comes back again to the heart ;

(c) that the blood leaves the left side of the heart by the
arteries and returns to the right side by the veins.

(d) that the blood travels from the right side of the heart
to the left side by way of the lungs.

Johannes Muller (1774-1842)

(a) He had a famous laboratory at Berlin where, with
his students, he carried out extensive investigations in
Physiology.

(b) He invented many different kinds of apparatus with
which to carry out these investigations,

SUMMARIES 291

II

Discoveries with the Microscope
Marcello Malpighi (1628-1694)

(a) He examined the air passages in the lungs and saw
the tiny blood-vessels connecting the veins and the
arteries.

(b) He discovered the red corpuscles in the blood.

(c) He found several layers to the skin.

(d) He studied the anatomy and the life-history of the
silkworm, and discovered the mechanism by which it
produces silk.

(e) He studied and made the first drawings of plant cells.

Jan Swammerdam (1637-1680)

(a) He made an especial study of insects, and became
very skilled in dissecting them and examining them under
the microscope.

(b) He made very beautiful drawings of what he found.

Anthony van Leeuwenhoek (1632-1723)

(a) He examined a very great variety of things under his
microscopes, which he made himself.

(b) He also discovered the capillaries connecting arteries
and veins. He first saw them in the tail of a tadpole.

(c) He discovered the Protozoa in pond water and found
that they continued to live when the water dried up.

Schwann

(a) He maintained that the unit from which all living
things were built was the cell.

(b) He thought, wrongly, that the most important thing
about the cell was its wall.

Max Schultze

He showed that the essential part of the cell was the
protoplasm, since some animal cells have no wall.

292 THE ROAD TO MODERN SCIENCE

Red:

(a) He showed that the maggots which always appeared
in decaying meat did not spring spontaneously from the
decay, but were hatched from eggs which flies had laid
on the meat.

(b) He further showed that, in all cases where life
apparently sprang from dead matter, germs of life had
somehow been introduced.

Louis Pasteur (1822-1895)

(a) He showed that bacteria are floating everywhere in
the air, but that pure country or mountain air contains
far fewer than the air in cities and inside houses.

(b) He discovered that the fermentation of sugar to
produce alcohol, the souring of milk, and the growth of
a mould on cheese were each due to the action of a par-
ticular kind of bacteria. With his microscope he
identified these bacteria in each case.

(c) He found that the cause of silkworm disease was due
to a germ, and showed how the disease could be com-
bated.

(d) He introduced the use of vaccines as a preventative
against certain forms of infectious diseases.

(e) The Pasteur Institute in Paris was built to enable the
study of Bacteriology to be carried on.

Robert Koch

(a) He was a contemporary of Pasteur and discovered the
germs of Anthrax in the blood of sheep suffering from
the disease. This was the starting-point of Pasteur's
work on vaccines.

(b) He also discovered the germ producing tuberculosis
and cholera.

Jermer (1749-1823)

He was responsible for the introduction of vaccination
against smallpox.

SUMMARIES 293

Sir Joseph Lister (1827-1912)

He introduced the antiseptic method into surgery. This
he did as a result of Pasteur's work.

Ill

The Relationship between the Various Forms of Life
Aristotle

He made the first attempt at classification, but dealt
chiefly with animals.

Karl Linnaeus (1707-1778)

He introduced the system of classification which is used
in much the same form to-day.

Georges Cuvier (1769-1832)

(a) He studied as many different types of animals as
possible, and compared their structures and the function-
ing of their organs. This study is known as Comparative
Anatomy.

(b) He examined the fossils in the gypsum mines, near
Paris, and discovered that some of the bones belonged
to. animals no longer known on earth (extinct).

(c) After many years spent in studying fossils he came to
the conclusion that at certain times some types of animals
became extinct, and new ones were formed.

(d) He believed these changes to be due to catastrophes
such as widespread flood.

Jean Baptiste Lamarck (1749-1829)

(a) He also studied fossil remains, but confined his
attention chiefly to invertebrates.

(b) He disagreed with Cuvier in thinking that certain
forms died out and were replaced by others at certain well-
defined times. He was of the opinion that the changes
were very gradual and that there was a succession of
closely related types to be found.

294 THE ROAD TO MODERN SCIENCE

(c) He was confirmed in this opinion by the discoveries
of the English geologist William Smith. The latter
found that the surface layer of the earth is made up of
a number of strata which always appear in the same
order. These strata are characterised by the fossils
which they contain. Fossils in one layer often show
small but quite definite differences from similar fossils
in the nearest layer of the same kind.

(d) To explain this evidence of the existence of succession
of forms of life he advanced the theory of Evolution by
Inheritance of Acquired Characteristics.

N.B. The theory of evolution is now generally accepted,
but not Lamarck's particular explanation that it occurred
by the inheritance of acquired characteristics.

Charles Lyell (1797-1875)

(a) He was an English geologist.

(b) By studying the changes which are going on in the
earth's crust now, he tried to understand the changes
which have taken place in the past.

(c) In this way he explained the formation of layers and
the fossils found embedded in them.

(d) By studying the rate at which layers are now being
built up he was able to calculate the period of time in
which any given stratum was laid down. In this way
he fixed definite eras during which certain forms of life
existed.

Charles Darwin (1809-1882)

(a) He went round the world in H.M.S. Beagle as
Naturalist. In this way he collected an enormous
number of specimens on the study of which his future
work was based.

(b) The study of these specimens convinced him of the
fact of Evolution.

(c) The explanation he gave differed from that of
Lamarck. It is generally known as Natural Selection by
the Survival of the Fittest.

SUMMARIES 295

(d) He published his evidence for Evolution, together
with his explanation as to how it came about, in his
famous book The Origin of Species.

IV

Heredity

(1) New organisms are formed by the fusion of male and
female gametes.

(2) Male gametes are small and easily detached from the
parent (e.g. pollen grains).

(3) Female gametes are larger and remain attached to the
parent (e.g. ovules).

(4) The fusion of a male with a female gamete is known as
fertilisation and produces a Zygote.

Gregor Mendel (1822-1889)

(a) He studied the inheritance of certain characteristics
of garden peas of which he grew several generations.

(b) He came to the conclusion that characteristics usually
go in opposite pairs. He called these * factors.'

(c) He supposed that any one gamete can only carry one
of a pair of factors.

(d) He further came to the conclusion that, in any pair
of factors, one was 'dominant' and the other * recessive.'

(e) Any zygote carrying both factors of a pair will itself
show the characteristic of the dominant factor, although
it may pass on the recessive character to its offspring.
Only zygotes carrying a double dose of the recessive
factor exhibit the corresponding characteristic.

SUMMARY TO CHAPTER XVI

A. The Inside of the Atom :

(d) The atom consists of a heavy positive nucleus
surrounded by rings of electrons.

296 THE ROAD TO MODERN SCIENCE

(b) The greater part of the bulk of an atom is empty
space.

(c) Atoms of elements heavier than lead and bismuth
are unstable. These elements are known as radio-active
elements.

(d) Becquerel discovered Uranium, and M. and Mme
Curie discovered Radium.

(e) Professor Soddy investigated the disruption of the
nucleus of radio-active substances. Three kinds of
radiations are given off :

(1) Alpha Rays particles which carry a positive
charge.

(2) Beta Rays particles which are electrons and
therefore negatively charged.

(3) Gamma Rays which are really very short X-rays.
They are known as Becquerel Rays.

(/) Lord Rutherford, by bombarding certain gases with
alpha particles, succeeded in knocking bits off some of
the nuclei and so forming another kind of element.

B. Exploring the Universe:

(a) Professor Einstein has shown that Newton's Laws do
not hold accurately in the vastness of the universe ; nor
in the minute world of the atom.

(b) He has supplied others in their place.

C. Modern biologists are working along three main lines :

(1) The study of Heredity.

(2) The study of the Laws of Health.

(3) The study of the Human Mind.

SUBJECT INDEX

ABSOLUTE zero, 191.

Academic des Sciences, 68, 91,

97-

Academy at Athens, 21, 22, 28.
acids, 87, 88, 96, 100.

vegetable, 98, 107.
acquired characteristics, 252, 257.
aeroplane, 165.
air, 19, 24, 25, 37, 83, 87 ff., 178.

alkaline, 88.

fixed, 84, 88.

inflammable, 87.

thermometer, 169, 170.
alchemists, 47, 77, 82, in.
alchemy, 36, 37, 41, 42 ff.
alcohol, 107, 239.
Alexandria, 27 ff., 35, 37, 38.
algebra, 40.
alkaline air, 88.
alkalis, 82 ff.

caustic, 82, 97, 101, 102, 131.

mild, 82, 101.
Almagest, 32.
Alpha rays, 266, 269.
altitude of star, 49, 65 (plate),
ammeter, 132.
ammonia, 44, 88.
ammonite, 251, 240 (plate),
amps, 132.
anatomy, 221, 230, 249.

of insects, 231.
aneroid barometer, 154.
angiosperma, 247.
angle of dip, 115.
animals, 220, 230, 233, 239, 248,

254-
Animal Kingdom, 246, 247.

anthrax, 240 ff.
antiseptic method, 245.
apparatus, chemical, 39.

Priestley 's, 88, 87 (plate),
aqua fortis, 44.

regia, 44.

297

Arabian Science, 39 ff.
Arabs, 28, 38, 42.
arteries, 225, 227, 228.
articulated animals, 248.
aseptic method, 245.
astrology, n, 38, in.
Astronomer Royal, 201, 207, 208.
astronomy, n, 32, 49, 51, 53, 66,

67, 7i> 155, iQ7ff- 270-
atom, 105, 234, 263, 271.
structure of, 264 ff.
of hydrogen, 264; of helium,
265 ; of lithium, 265 ; of
lead, 265 ; of bismuth, 265.
Authority, 40, 41, 46, 221, 223,

224.
azote, 95, 96.

BABYLONIANS, 8 ff.
bacteria, 236 ff.
barium, 102.
barometer, 64, 154.

aneroid, 154.
battery, 102, 130, 143.
Beagle, 255-
Becquerel rays, 266.
bell -jar experiment, 94.
benzene molecule, 108, 109.
beta rays, 266.
Black Magic, 36.
blood, 19, 225 ff., 241.
botany, 220.
broadcasting, 193.
bromine, 101.
bronze, 10.
bunsen burner, 216.
burning, 23, 80, 95.

CALCIUM, 102.
calculus, 68.
calendar, 7.
caloric, 169, 170, 174.
calorie, 171, 177.

298 THE ROAD TO MODERN SCIENCE

calx, 81, 95.

red mercury, 89, 95.
capacity, electrical, 126.

for heat, 172.
capillaries, 228, 230, 232.
carbon, 96, 168.
carbon dioxide, 84.
Carnivora, 247.
caustic alkalis, 82, 97, 101, 102,

131-

Cell, the Simple, 130.
Cell Theory, 233, 234.
cells, plant, 231, 233, 234-

animal, 234.
chalk, 8 1 ff.
chemical action and heat, 169.

decomposition by electricity,

131-

energy, 176.

theory, 102 ff.
chemistry, 44, 66, 77 ff.

organic, 107.
chlorine, 98, 100.
circulation of the blood, 224 ff.,

226.

Classes, 246.
classification, 23.

Cuvier's, 248.

elements, 106.

Linnaean, 246, 247.
clepsydra, 12.
Combustion, theory of, 95,

97-

comet, 200.
compass, 112.
condenser, electrical, 126, 127.

Watt's, 161.

conductivity, electrical, 127.
conductor, electrical, 119, 127.
conservation of energy, 178.

of mass, 104.
constellations, 8, n.
copper, 9, 10, 44.
Copernican system, 51, 53, 56,

60, 61, 63.
corpuscular theory of light,

i84fT.

cosmic rays, 196.
cow-pox, 242.

DARK Ages, 35 ff.
dentists' gas, 99.
dephlogisticated air, 89, 90.
De Revolutionibus Orbium Cales-

tium, 50.

dicotyledons, 247.
dip needle, 116.
disease, 19, 240 ff.

of cancer, 266.

of silkworms, 240.
dissection, 25, 221, 222.

of insects, 231.
dominant character, 261.
dyes, 109.
dynamics, 71.
dynamo, 142, 176.

EARTH, 19, 24, 25, 37, 43.

the, 25, 32, 49, 53, 72~74> *97,

200, 213, 2l8, 271.

earths, 101, 102.
echo, 179.
eclipse, 32, 51.

of Jupiter's moons, 210 ff.

Egypt, 17, 27.

Egyptians, 5 ff., 28, 36.
electric charge, 264.

circuit, 133, 134.

current, 124, 128 ff.

motor, 143, 167.
electrical capacity, 126.

energy, 176.

machines, 120.

pressure and potential, 124 ff.

terms, 132.
electricity, 16, 87, no, 117.

connection with magnetism,

131-

negative, 122, 264.

positive, 122, 264, 268.

* resinous,' 118.

'vitreous,' 118.
electrics, 117, 119.
electromagnetic induction, 137 ff.
Electromotive Force, 133.
electron, 16.

electrons, 264, 265, 269, 270.
electro-plating, 131.
element, definition, 79.

SUBJECT INDEX

299

elements, 17, 79, 85, 87, 93, 101,

103, 106, 169, 172, 216.
classification, 106.
four, 19, 24, 37, 43, 45-
Lavoisier's list, 96, 98, 101,

102.

elixir of life, 45.
ellipse, 22, 55, 71, 200, 204.
emission theory of light,

184 ff., 190.
energy, 176 ff., 191.
conservation, 177.
engine, 157.

high-pressure steam, 162.
internal combustion, 163, 164.
Newcomen's, 158.
Watt's, 161.
epicycles, 33, 35-
ether, 144, 185, 191, 194, 214.
evolution, 252, 255 ff.
expansion, 169.
experiment, 26, 29, 46.

Faraday's, on electromagnetic

induction, 137 ff.
Franklin's kite (experiment),

122.

Guericke's, to show atmo-
spheric pressure, 156, 157.
Lavoisier's, to prove theory of

combustion, 94.
Mendel's, with peas, 258.
Newton's, with prism, 70.
Pasteur's, on inoculation, 242.

FACTOR, 261.

falling bodies, 24, 59, 72.

families, 246.

Faraday Exhibition, 134, 137.

Father of Experimental Science,

of Medicine, 20.

of Modern Chemistry, 78.
felidae, 247.
felis domesticus, 247.

leo, 247.

tigris, 247.
female gamete, 258.
Ferme Gnral, 91.
fermentation, 239.

fertilisation, 259, 260.
fire, 19, 24, 25, 37, 80.
fixed air, 84 ff., 88.
fluorine, 101.
flying machines, 47.
focus, of ellipse, 56.
force, 146, 175.

of gravity, 71 ff., 147, 203.

field of magnetic, 140.

lines of magnetic, 144.
fossils, 240 (plate), 249, 250, 256.
Four Elements, 19, 24, 37, 43,

45, 79-
humours, 19.
fourth dimension, 271.
Fraunhofer lines, 215, 218.
French Revolution, 86, 91, 248.
friction, 173, 176, 177.
fuel, 143, 163.

GALVANOMETER, 132.

Galileo's thermometer, 169, 170.

gametes, 258, 261.

gamma rays, 266.

gangrene, 224.

gases, 88, 89, 102, 191.

genera, 247.

genus, 246.

geology, 66, 253.

geometry, 6, 7, 16, 21, 29, 46,

213.

germs, 236 ff.
glass, 13, 39> ii7, 215-

vita-, 192.

gold, 10, 30, 31, 36, 39, 43, 44, 80.
Graf Zeppelin, 166.
Greek philosophers, 15 ff., 150.
Greeks, 3, 5, 15 ff., 28, 37, 40,

50, 63, 178, 252.
gypsum, 248.

HALOGEN family, 101.

heart, 225.

heat, 24, 96, 169 ff., 203.

and chemical action, 169.

capacity, 172.

latent, 170.

mechanical equivalent, 177.

radiant, 190, 191.

300 THE ROAD TO MODERN SCIENCE

heavenly bodies, 43, 51 , 52, 61,

u ,. I97 '
hehometer, 213, 214.

helium, 218, 264, 269.
Herald of the Dawn, 46.
heredity, 258 ff., 272.
humours, four, 19.
hydrochloric acid, 44, 100, 101.
hydrogen, 90, 96, 100, 106, 108,

264.

chloride, 88.
hydrophobia, 243.
hypothesis, 103.

ICE, 170, 171, 174.
induced currents, 140.
induction, 137.
Industrial Revolution, 162.
inertia, 179.

inheritance, 256, 257, 258 ff.
of acquired characteristics,

257.

inherited characters, 259 ff.
inorganic substances, 107.
insects, 231, 248.
instruments, 59.

astronomical, 40, 52, 212.
insulators, 126.
interference, 189.
internal combustion engine,

163 ff.

inverse square law, 72, 124.
invertebrates, 246, 250.
iodine, 101.
lonians, 15, 17.
iron, 10, 15, 44, 87, 140.

JUPITER, n, 53, 210 ff.
Jupiter's moons, 60, 61, 205,
210 ff.

KING HIERO'S crown, 30.

LATENT heat, 170, 171.
law of conservation of mass,
104.

of constant proportions, 104.

of electrical force, 118, 124.

law of gravitation, 72, 73, 202,
203, 206, 271.

Ohm's, 133.

lever, 7, 30.

magnetic force, 114.
laws of motion, 271.
lead, 44, 265.

lenses, 40, 60, 69, 230, 232.
lever, 7, 146, 147, 148.
lever law, 7, 30.
Leyden Jar, 119, 120, 121, 127,

130.
life, 220, 135, 272.

animal, 250, 263.

forms of, 246 ff., 254.
light, 40, 46, 67, 96, 144, 168,
183 ff., 209, 214.

interference of, 189.

properties of, 183.

velocity of, 183, 210.
light-year, 213.
lightning, 122.

conductor, 123.
lime, 96, 102.
lines of force, 139.
liquids, 191.
lithium, 265.
litmus, 88.
Little Bear, in.
lodestone, 16, 112.
logic, 22, 24.

longitudinal vibrations, 189.
Lyceum at Athens, 23, 25, 27, 28.

MACHINES, 7,29,47, 146 ff., 176,

271.

Magdeburg hemispheres, 156.
magnesia, 96, 102.

alba, 81.
magnesium, 102.
magnet, 16, in ff., 137.
magnetic declination, 116.

dip, 115.

field, 139 ff., 144.
magnetism, noff.

connection with electricity,

131, 137 ff.

magnifying glass, 89, 232.
male gamete, 258.

SUBJECT INDEX

301

mammalia, 247.
mammals, 247.
manuscripts, 28, 38, 41.
maps, 33.

magnetic, 117.
star, ii, 203, 206, 208.
marine acid gas, 88, 100.
mariners' compass, in.
Mars, 53.

mathematics, 18, 28, 31, 47, 48,
53,59,66,67, 132, 144, 198,
206.
measurement, importance of, 87,

93,227.
distances of heavenly bodies,

212, 213.
distances between stars, 202,

213.

force, 123.

land, 6, 16.

latent heat, 171.

velocity of light, 210 ff.
mechanical equivalent of heat,

177.

mechanics, 29.
medicine, 19, 40, 45, 66.
mercury (element), 43, 88, 89,

151, 237-

principle of, 45.
Mercury (planet), n, 53, 54.
meridian, 49.

metals, 9, 10, 36, 39, 43, 80,

88, 93, 95, 96, 102, 129.
metal working, 9, 10, 13, 36.
micro-ray, 196.
microscope, 228, 229 ff., 232.
mirrors, 199.
molecular weight, 106.
molecule, 105, 108, 175, 191, 270.

of benzene, 108, 109.

of naphthalene, 108, 109.
molluscs, 248.

moon, the, 7, n, 25, 72, 204.
Morse Code, 132, 133.
motion, 64, 147, 174, 176.
motions of the planets, 73, 197.

of the fixed stars, 203, 219.
motor-car, 165.
motor-cycle, 165.

mould, 235, 239.

muriatic acid, 100.

Museum of Alexandria, 27 ff ., 36.

music of the spheres, 19.

musical notes, 18.

NAMES, chemical, 96.
naphthalene, 108, 109.
Natural Selection, 257.
Naturalists' Voyage in H.M.S.

Beagle, A, 256.
Nature, 20.

abhors a vacuum, 151.
nebulae, 200, 201, 204, 205, 219.
Nebular Hypothesis, 205.
Neptune, 205 ff., 213.
Nile, 5, 6.
nitric acid, 44.
nitrogen, 96, 269.

oxides of, 88.
non-conductor, 119.
non-electrics, 117.
north, geographical, in.
nucleus (of cell), 233.

(of atom), 264 ff., 270.
number, 3, 9, 18.

OBSERVATORY, Uranienburg, 52.

Mount Wilson, 209.
Ohm's law, 133.
oil of vitriol, 87.
Op ticks, 74.
optics, 67, 69, 198.
Opus Mains, 46, 112.

Minus, 46.

Tertium, 46.
orbit, planets, 50, 203, 204.

Uranus, 200.

the earth, 211, 213.
orders, 246.
organic chemistry, 107.
organism, 258.
Origin of Species, The, 256.
oscillations, 179.
ovules, 258, 259.
oxides of nitrogen, 88.
oxygen, 90, 95, 96, 98, 100, 108,
229, 237-

302 THE ROAD TO MODERN SCIENCE

PAPER, 5, 40.
parabola, 74.
Pasteur Institute, 243.
pendulum, 59, 203.
"peripatetic philosophers, 23.
petrol engine, 165, 167.
philosopher's stone, 39, 43, 45.
philosophy, 15, 16, 17, 28.
phlogiston, 80, 90, 92.

theory, 80, 89.
Phoenicians, 12.
phosphorus, 93, 96.
phyla, 246, 247.
physics, 24, 66, 87, 204, 220.
physiology, 66, 220, 221, 224,

229.
Pisa, 58, 59.

leaning tower of, 24, 39.
planets, n, 14, 22, 49, 5, 53,
7i 73, 155, 197, 200, 201,
202, 203, 205, 213, 264.
plants, 220, 233, 239-
Pluto, 209.

Pneumatic Institute, 99.
pneumatic trough, 88.
pole star, in.
poles, geographic, 48, 113.

of a magnet, 112, 113, 140.
pollen, 258, 259.
Pope, the, 40, 41, 51, 57, 62.
potassium, 102.
potential, 124.
power, 146 ff.

mechanical, 146.

steam, 143.

water, 143.
pressure of atmosphere, 152 ff.

barometric, 182.
primary qualities, 24.
Principia, 74.
principle, acidifying, 100.

of conservation of energy, 178.
principles of Paracelsus, 45, 79.
prism, Newton's experiment, 70.
propeller, 166.
protons, 264.
protoplasm, 254.
protozoa, 233, 236, 252.
psychology, 220.

pulleys, 147, 148, 149-
pump, suction, 149, 150, 155.
pyramids, 7, 146.

QUADRANT, 49, 50, 65 (plate),
quick-lime, 82, 101.

RADIANT heat, 190, 191.
radio-active substances 266.
radium, 193, 266, 267.
Ranunculaceae, 247.
Ranunculus, 247.
recessive character, 261.
red mercury calx, 89, 94.
reflection, 183, 191.
refraction, 183, 191.
resistance, 133.
Romans, 28, 31, 35, 36, 41, 81,

149.

Rontgen rays, 192.
Royal Institution, 99, 102, 131,

135, 136, 172, 186.
Royal Society, 68, 78, 86, 91, 97,

100, 158, 232.
Rudolphine Tables, 53, 54, 55.

SAFETY lamp, 100.
salt, principle of, 45.

spirits of, 44.
satellites, 204.

of Jupiter, 61.
Saturn, 53, 60, 200, 204.
Sceptical Chymist, 78.
shadows, 183, 185.
Signs of the Zodiac, u, 12.
silkworms, 230, 240.
silver, 10, 30, 31, 43, 80.
Sirius, 202.
smallpox, 242.
sodium, 102, 216.
solar system, 197, 202 ff., 230,
264, 265.

origin of, 205.
solids, 191.
sound, 18, 168, 1781!.

velocity of, 179, 182.

waves, 181.
souring of milk, 239.

SUBJECT INDEX

303

space-time, 271.

species, 246.

spectra of elements, 216.

of stars, 215.
spectrometer, 216, 217.
spectrum, 69, 190 ff., 214 ff.

analysis, 214 ff.

continuous, 217.
spermatophyta, 247.
spirits of salt, 44.

of hartshorn, 44.
starfish, 248.

star-maps, n, 203, 206, 208.
stars, 8, n, 209, 219, 270.

double, 200, 201, 205.

fixed, 25,49, 197-

variable, 200.
Stars and Atoms, 270.
steam- car, 165.

-engines, 157 ff.

power, 143.
strata, 250, 251, 254.
suction-pump, 149, 150, 155.
sulphur, 43, 93, 96.

principle of, 45.

sun, 7, 10, n, 49, 54, 191, 197,
200, 202, 203, 204, 205, 209,

213, 217, 218, 264, 270.
survival of the fittest, 256.
Syrians, 38.

TELEGRAPH, no, 132.
telephone, no, 143, 194.
telescope, 60 ff., 69, 71, 199, 201,

214, 229.
temperature, 170, 182, 191.

of stars, 219.
terrella, 113, 115.
terrestrial magnetism, 114*!.
theorems, 16, 18.
thermometers, 169, 170.
Three Principles, 45, 79.
time, 271.

measurement of, 12, 59.
tin, 10, 44.

TraitS de Chemie, 92, 98.
transit, 49.

transmutation of matter, 37, 43,
271.

transverse vibrations, 189.
trigonometry, 40.

ULTRA-VIOLET rays, 192.
units, electrical, 132.

astronomical, 213.

of heat, 171, 172.
Universe, 25, 32, 50, 197, 202,

219, 263, 264, 270, 271.
Universe of Light, The, 213.
Uranienburg, 52.
uranium, 266.
Uranus, 201, 206, 209.

perturbations of, 207.
urea, synthesis of, 108.

VACCINATION, 243.
vaccine, 242.
vacuum, 150, 152, 155.
valves, 149, 150.

of veins, 225, 226.
Vegetable Kingdom, 246, 247. -
veins, 225, 227, 228.
velocity of light, 183, 194.

of sound, 179.

of wireless waves, 194.
Venus, n, 53.

vertebrates, 246, 247, 248, 250.
vita-glass, 192.
voltage, 124.
voltaic pile, 101, 130.
volume, 30, 31.

WATER, 17, 19, 24, 25, 31, 37, 43,
87, 97, 151, 174.

composition, 90.

decomposition by electricity,
101.

-clock, 12.

-power, 143.

-pump, 149.

-waves, 179 ff.

wave-length, 190, 194, 195, 214,
218, 219.

-motion, 179, 189.

theory of light, 184 ff., 190.
waves, 144, 169 ff., i79 214.

infra-red, 195.

304 THE ROAD TO MODERN SCIENCE

X-RAYS, IQZ, 193, 266.

.waves, sound, 181, 194.

wireless, 144, 193.
weight, atomic, 106.

importance of, 83, 85, 88,

93-

molecular, 106.
weights and measures, 18, 92.
wireless waves, 144, 193.
work, 175.

YEAST, 239.

Zeppelin , the Graf> 166.

zenith, 49.

Zodiac, Signs of, n, 12.

zoology, 220.

zygote, 260, 261.

INDEX OF NAMES

ADAMS, 206 ff.

Alexander the Great, 21, 22, 27.

Ampere, 132.

Aquinas, 41.

Archimedes, 29 ff., 149.

Aristarchus, 50.

Aristotle, 19, 21, 22 fT., 27, 28,

32, 37, 41, 42, 45, 48, 50, ss,

58, 79, 220, 221, 246.
Astronomer Royal, 201, 207, 208.
Avicenna, 45.

BACON, ROGER, 46, 64, in, 112.

Becquerel, 266, 267.

Berthollet, 100, 104.

Berzelius, 104, 106.

Bessel, 213, 214.

Black, 81 ff., 97, 170.

Boyle, 78 ff., 81, 98, 105, 107,

158, 169.
Bragg, 213.
BranS, 51 ff., 54, 56.
Brougham, Lord, 186.
Bruno, 51, 60.
Bunsen, 215, 216.

CAVENDISH, 81, 86 ff., 97, 121,

123 ff., 268.
Copernicus, 48 ff., 62.
Curie, M. and Mme, 266, 267.
Cuvier, 247.

DAIMLER, 165.
Dalton, 103 ff., 264.
Darwin, 225 ff., 258.
Davy, 98 ff., 131, 135, 174.
Dufay, 118, 122.

EDDINGTON, 270.
Einstein, 270 ff.
Euclid, 29.

FABRICIUS, 225, 226.
Faraday, 99, 131, I34 ff -
Fizeau, 212.
Franklin, 86, 121.
Fraunhofer, 214 ff.
Fresnel, 189.

/ * , *o * > * v y> **
Galvani, 128, 132
Gilbert, 113 ff.
Guericke, 154 ff.

HALLEY, 203.

Harvey, 224 ff.

Herschel, Sir William, 190, 192,

197 ff., 204, 205, 206, 213.
Herschel, Caroline, 198, 199,

201, 202.
Hertz, 144, 193.
Hipparchus of Nicea, 212.
Hippocrates of Cos, 19.
Hooke, 78, 158.
Huyghens, 184 ff., 188, 189.

JENNER, 242.
Joule, 177.

KEPLER, 22, 51, 53 ff., 155.
Kirchoff, 215, 217.
Koch, 240.

LAMARCK, 250.
Laplace, 202 ff.
Lagrange, 203.
Lavoisier, 91 ff., 97, 100, 107,

169, 172.

Leeuwenhoek, 230, 231.
Leonardo da Vinci, 46, 64, 112,
149, 179, 249.

305

306

THE ROAD TO MODERN SCIENCE

Leverrier, 207 ff.
Linnaeus, 246.
Lister, 244.
Louvrier, 241.
Lyell, 253.

MALPIGHI, 230.
Marconi, 193.
Maxwell, 144, 193,
Mayer, 175.
Mendel, 258.
Miiller, 229, 234.

NAPOLEON, 173, 202, 250.

Newcomen, 158.

Newton, 57, 64, 66 ff., 105, 124,

i55> 169, 179, 182, 197, iQ9,

202, 263, 270.

OHM, 133.
Oersted, 131, 141.

PAPIN, 157 ff.

Paracelsus, 44 ff., 77. 79, 224.

Pascal, 152 ff.

Pasteur, 237 ff.

Peregrinus, 112.

Perrier, 153.

Plato, 21, 23, 28, 32, 37, 4 1 , 55,

58.

Pope, the, 40, 41, 51, 57, 62.
Pouchet, 237.
Priestley, 81, 85 ff., 93, 96, 97,

121, 229.
Proust, 104.
Ptolemy, 27, 35-
Ptolemy the Egyptian, 31, 35, 48,

50,52, 55-

Pythagoras, 6, 17 ff., 21, 29, 50,
178.

I, 235, 236.
Roemer, 183, 210.
Rontgen, 192.
Rumford, 99, 172 ff.
Rutherford, 268, 269.

SCHEELE, 97 ff., 100, 1 06.
Schultze, 234.
Schwann, 234.
Smith, 250.
Snell, 183.
Socrates, 21.
Soddy, 267.
Swammerdam, 230, 231.

THALES, 15 ff., 19, 29, 35, no.

Thompson, 172.

Thomson, 268.

Torricelli, 64, 151 ff.

Tuscany, Grand Duke of, 62,

149.
Tyndall, 178.

VINCI, LEONARDO DA, 46, 64, 112,

149, 179, 249.
Vesalius, 222.
Volta, 101, 129 ff.

WATT, 160.

Wohler, 108.

Wright, Wilbur and Orville, 167.

YOUNG, 1 86 ff., 192.
ZEPPELIN, COUNT VON, 166.