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SUN SODIUM HYDROGEN STAR, NEBUUE

SPECTRUM ALDEBARAN

A SHORT HISTORY

OF

NATURAL SCIENCE

A.ND OF THE

PROGRESS OF DISCOVERY FROM THE TIME OF THE
. GREEKS TO THE PRESENT DAY

FOR THE USE OF SCHOOLS AND YOUNG PERSONS

By ARABELLA :^"bUCKLEY -

WITH ILLUSTRATIONS

BOSTON COVkJm^ UBI^AKY
CHESTKUT HII^ M^^^

^ NEW YORK:
D. APPLETON AND COMPANY,

549 AND 551 Broadway.
1876.

67073

f 0 i^t 9^mox^ of

MY BELOVED AND REVERED FRIENDS

SIR CHARLES and LADY LYELL

TO WHOM I OWE MORE THAN I CAN EVER EXPRESS

TRUSTING THAT IT MAY HELP

TO DEVELOPE IN THOSE WHO READ IT THAT

EARNEST AND TRUTH-SEEKING SPIRIT IN THE STUDY OF GOD'S

WORKS AND LAWS WHICH WAS THE GUIDING

PRINCIPLE OF THEIR LIVES

i

PREFACE

It is not without some anxiety that I offer this Httle
work to the public, for it is, I believe, the first at-
tempt which has been made to treat the difficult
subject of the History of Science in a short and
simple way.i

Its object is to place before young and unscien-
tific people those main discoveries of science which
ought to be known by every educated person, and at
the same time to impart a living interest to the whole,
by associating with each step in advance some history
of the men who made it.

During the many years that I enjoyed the privi-
lege of acting as secretary to the late Sir Charles
Lyell, and was thus brought in contact with many of
the leading scientific men of our day, I often felt very
forcibly how many important facts and generaliza-
tions of science, which are of great value both in the
formation of character and in giving a true estimate

* Mr. Baden Powell's excellent little ' History of Natural Philo-
sophy,' published in Lardner's 'Cyclopaedia' in 1834, is scarcely
intended for beginners, and does not extend farther than the seven-
teenth century. This is the only work of the kind I have been able to
find.

VL PREFACE,

of life and its conditions, are totally unknown to the
majority of otherwise well-educated persons.

Great efforts are now being made to meet this
difficulty, by teaching children a few elementary facts
of the various branches of science ; but, though such
instruction is of immense value, something more is
required in order that the mind may be prepared to
follow intelligently the great movement of modern
thought. The leading principles of science ought
in some measure to be understood ; and these will,
I believe, be most easily and effectually taught by
showing the steps by which each science has attained
its present importance.

It is this task which I have endeavoured to ac-
complish ; and if teachers will make their pupils master
the explanations given in these pages and, wherever
it is possible, try the experiments suggested, I venture
to hope that this little work may supply that modest
amount of scientific information which everyone
ought to possess, while, at the same time, it will form
a useful groundwork for those who wish afterwards to
study any special branch of science.

The plan adopted has been to speak of discoveries
in their historical order, and to endeavour to give such
a description of each as can be understood by any
person of ordinary intelligence. This has made it
necessary to select among subjects of equal impor-
tance those which could be dealt with in plain lan-
guage, and to avoid passing allusions to such as did
not admit of such explanation.

PREFACE. vii

The history of the nineteenth century has been a
very difficult and I fear scarcely a successful task ;
for, while those who know anything of the subjects
mentioned, will feel that the accQunt is very defective
owing to so much being left out, the beginner will
probably find it difficult owing to so much being put
in. The reproach on both sides would be just, yet it
seemed better to give even a few of the leading dis-
coveries and theories of our own time than to leave
the student with such crude ideas of many branches
of science as he must have had if the history had
ended with the eighteenth century.

When treating of such varied subjects, many of
them presenting great difficulties both as regards
historical and scientific accuracy, I cannot expect to
have succeeded equally in all, and must trust to the
hope of a future edition to correct such grave errors
as will doubtless be pointed out, in spite of the care
with which I have endeavoured to verify the state-
ments made.

As the size of the book makes it impossible to
give the numerous references which would occur on
every page, I have named at the end of each chapter
a few of the works consulted in its preparation, choos-
ing always in preference those which will be useful to
the reader if he cares to refer to them. I had also
prepared questions on the work ; but those competent
to give an opinion, tell me that teachers in these days
prefer to prepare their own lessons. I have there-
fore substituted, at p. 439, a chronological table of the

viii PREFACE.

various sciences, by means of which questions can be
framed, either upon the discoveries of any- given
period, or on the progressive advance, through several
centuries, of any of the five main divisions of science
which are dealt with in this volume.

In conclusion, I wish to acknowledge my obliga-
tions to many kind friends, and especially to Mr. A.
R. Wallace and Mr. J. C. Moore, F.R.S., who have
rendered me very material and valuable assistance.
I am also much indebted to the Rev. R. M. Luckock, of
the Godolphin Grammar School, who read the whole
work in manuscript, with a view to pointing out any
portions which might be unintelligible to schoolboys.

London : December 1875.

CONTENTS.

PAGE

Introduction , , . i

PART I.

SCIENCE OF THE GREEKS.

CHAPTER I.

639 TO 470 B.C.

Ignorance of the Greeks concerning Nature — Ionian School of
Learning — Thales discovers the Solstices and Equinoxes, and
knows that the Moon Reflects the Light of the Sun — Anaxi-
mander invents a Sun-dial — Discovers the Phases of the Moon —
Makes a Map of the Ancient World — Pythagoras teaches that

■ the Earth moves, and that the Morning and Evening Star are
the same — He studies Geology, and knows that Land has in
some places become Sea — True sayings of Pythagoras and his
Followers about Geology ....... 7

CHAPTER n.

499 TO 322 B.C.

Anaxagoras studies the Moon — Describes Eclipses of the Sun and
Moon — Is Tried and Condemned for Denying that the Sun is a
God — Hippocrates the Father of Medicine — Separates the
office of Priest and Doctor — Studies the Human Body —
Eudoxus has an Observatory — Makes a Map of the Stars —
Explains the Movements of the Planets — Democritus studies
the Milky Way — Aristotle an Astronomer and Zoologist —
Divides Animals into Classes — Teaches that there is a Gradual
Succession of Animal Life — Studies the Difference of the Life in
Plants and Animals — Theophrastus the first Botanist . -13

CONTENTS.

CHAPTER III.
320 TO 212 B.C.

PAGE

School of Science at Alexandria — The Ecliptic and the Zodiac —
Greeks believed that the Sun moved round the Earth — Aristar-
chus knew that it was the Earth which moved — He also knew
of the Obliquity of the Ecliptic, and that the Seasons are caused
by it — He knew that the Earth turns daily on its Axis — Euclid
discovers that Light travels in straight lines— Archimedes dis-
covers the Lever — Principle of the Lever — Hiero's Crown, and
how Archimedes discovered the principle of Specific Gravity —
Screw of Archimedes . . . . . . . .18

CHAPTER IV.

280 TO 120 B.C.

Erasistratus and Herophilus study the Human Body — Eratosthenes
the Geographer lays down the First Parallel of Latitude and the
First Meridian of Longitude — He measures the Circumference of-
the Earth — Hipparchus writes on Astronomy — Catalogues 1,080
Stars — Calculates when Eclipses will take place — Discovers the
Precession of the Equinoxes . . . . . . .25

CHAPTER V.

FROM A.D. 70 TO 200.

Ptolemy founds the Ptolemaic System — He writes on Geography
— Strabo, a great traveller, writes on Geography — Studies
Earthquakes and Volcanoes — Galen the greatest Physician of
Antiquity — Describes the Two Sets of Nerves — Proves that
Arteries contain Blood — Lays down a theory of Medicine —
Greece and her Colonies conquered by Rome — Decay of Science
in Greece — Concluding remarks on Greek Science . . 32

CONTENTS. xi

PART II.

SCIENCE OF THE MIDDLE AGES,

CHAPTER VL

SCIENCE OF THE ARABS.

PAGE

Dark Ages of Europe — Taking of Alexandria by the Arabs, and
burning of the Library — The Arabs, checked in their conquests
by Charles Martel, settle down to Science — The Nestorians
and Jews translate Greek Works on Science — Universities of the
Arabs — Chemistry first studied by the Arabs — Alchemy, or the
attempt to make Gold — Hermes the first Alchemist — Hermeti-
cally-sealed Tubes — Gases and Vapours called ' Spirits ' by the
Arabs — The use of this Word retained by us . . . .39

CHAPTER VII.
SCIENCE OF THE ARABS (CONTINUED).

Geber, or Djafer, the founder of Chemistry — His Explanation of
Distillation — Of Sublimation — Discovers that some Metals in-
crease in weight when heated — Discovers strong Acids — Nitric
Acid — Sulphuric Acid — Discovery of Sal-Ammoniac by the
Arabs — Arabs mix up Astronomy with Astrology — Albateg-
nuis calculates the Length of the Year — Mohammed Ben Muse,
first writer on Algebra — Uses the Indian Numerals — Gerbert
introduces them into Europe — Alhazen's discoveries in Optics —
His Explanation why only one image of each object reaches the
Brain — His discovery of Refraction, and of its effect on the light
of the Sun, Moon, and Stars — His discovery of the magnifying
power of rounded glas^ses ....... 43

CHAPTER VIII.

SCIENCE OF THE MIDDLE AGES IN EUROPE. '

Roger Bacon — His * Opus Majus ' — His Explanation of the Rain-
bow—He makes Gunpowder — Studies Gases — Proves a Candle
will not burn without Air — His Description of a Telescope —
Speaks of Ships going without Sails — Flavio Gioja invents the

xii CONTENTS.

Mariner's Compass — Greeks knew of the Power of the Load-
stone to attract Iron — Use of the Compass in discovering new
lands — Invention of Printing — Columbus discovers America —
Vasco de Gama sees the Stars of the Southern Hemisphere —
Magellan's ship sails round the World — Inventions of Leonardo
da Vinci. . . . . . . . . . • 5 ^

PART III.

RISE AND PROGRESS OF MODERN SCIENCE.

CHAPTER IX.

SCIENCE OF THE SIXTEENTH CENTURY.

Rise of Modem Science — Dogmatism of the Middle Ages —
Reasons for studying Discoveries in the order of their dates —
Copernican theory of the Universe — Copernicus goes back to
the System of Aristarchus — Is afraid to publish his Work till
quite the end of his Life — Work of Vesalius on Anatomy — He
shows that Galen made many mistakes in describing Man's
Structure — His Banishment and Death — The value of his Work
to Science— Fallopius and Eustachius Anatomists — Gesner's
Works on Animals and Plants — He forms a Zoological Cabinet
and makes a Botanical Garden — His Natural History of Animals
— His classification of Plants according to their Seeds — His
work on Mineralogy — Csesalpinus makes the First System of
Plants on Gesner's plan — Explains Dioecious Plants — Chemistry
of Paracelsus and Van Helmont ......

CHAPTER X.

SCIENCE OF THE SIXTEENTH CENTURY (CONTINUED).

Baptiste Porta discovers the Camera Obscura — Shows that our
Eye is like a Camera Obscura — Makes a kind of Magic Lantern
by Sunlight — Kircher afterwards makes a Magic Lantern by
Lamplight — Dr. Gilbert's discoveries in Electricity — Tycho
Brahe, the Danish Astronomer — Builds an Observatory on the
Island of Huen — Makes a great number of Observations, and

CONTENTS. xiii

PAGE

draws up the Rudolphine Tables —Galileo discovers the principle
of the Pendulum — Calculates the velocity of Falling Bodies, and
shows why it increases — Shows that Unequal Weights fall to the
Ground in the same time — Establishes the relations of Force and
Weight — Stevinus on Statics —Summary of the Science of the
sixteenth century 74

CHAPTER XI.
SCIENCE OF THE SEVENTEENTH CENTURY.

Astronomical discoveries of Galileo — The Telescope — Galileo ex-
amines the Moon, and discovers the Earth-light upon it — Dis-
covers Jupiter's four Moons — Distinguishes the Fixed Stars from
the Planets — The phases of 'Venus confirm the Copernican theory
— Galileo notices Saturn's Ring, but does not distinguish it
clearly — Observes the spots on the Sun — The Inquisition force
him to deny the movement of the Earth — Blindness and Death
of Galileo .......... 87

CHAPTER Xn.
SCIENCE OF THE SEVENTEENTH CENTURY (CONTINUED).

Kepler the German Astronomer — Succeeds Tycho as Mathema-
tician to the Emperor Rudolph — His description of the Eye —
He tries to explain the orbit of the planet Mars — And by com-
paring Tycho's tables with observation discovers his First and
Second Law of the movements of the Planets — His delight at
Galileo's discoveries — Kepler's Third Law — Comparison of the
labours of Tycho, Galileo, and Kepler . . . . -95

CHAPTER XIIL

SCIENCE OF THE SEVENTEENTH CENTURY (CONTINUED).

Francis Bacon, 1561-1626 — He teaches the true method of
■ studying Science in his 'Novum Organum' — Rene Descartes,
1 596-1 650 — He teaches that Doubt is more honest than Ignorant
Assertion — Willebrord Snellius discovers the Law of Refrac-
tion, 1621 — Explanation of this Law ..... 103

xiv CONTENTS.

CHAPTER XIV.
SCIENCE OF THE SEVENTEENTH CENTURY (CONTINUED).

PAGE

Fabricius Aquapendente discovers Valves in the Veins^Harvey's
discovery of the Circulation of the Blood — Discovery of the
Vessels which carry nourishment to the Blood — Gaspard Asellius
notices the Lacteals — Pecquet discovers the Passage of the fluid
to the Heart — Riidbeck discovers the Lymphatics . . .no

CHAPTER XV.
SCIENCE OF THE SEVENTEENTH CENTURY (CONTINUED).

Torricelli discovers the reason of Water rising in a Pump — Uses
Mercury to measure the Weight of the Atmosphere — Makes the
First Barometer — M. Perrier, at Pascal's suggestion, demon-
strates variations in the pressure of the atmosphere — Otto
Guericke invents the Air-pump — Working of the Air-pump —
Guericke proves the Pressure of the Atmosphere by the experi-
ment of the Magdeburg Spheres — He makes the first Electrical
Machine — Foundation of Royal Society of London and other
Academies of Science . . . . . . . .116

CHAPTER XVI.
SCIENCE OF THE SEVENTEENTH CENTURY (CONTINUED).

Boyle's Law of the Compressibility of Gases — ^This same Law dis-
covered independently by Marriotte — Hooke's theory of Air
being the cause of Fire — Boyle's experiments with Animals
under the Air-pump — ^John Mayow, the greatest Chemist of the
Seventeenth Century — His experiments upon the Air used in
Combustion — Proves that the same portion is used in Respira-
tion— Proves that Air which has lost its Fire-air is Lighter —
MayoVs ' Fire-air ' was Oxygen, and his Lighter Air Nitrogen
— He traces out the effect which Fire-air produces in Animals
when Breathing . . . . . . . . .128

CONTENTS.

CHAPTER XVII.
SCIENCE OF THE SEVENTEENTH CENTURY (CONTINUED).

PAGE

Malpighi first uses the Microscope to examine Living Stmctures
— He describes the Air-cells of the Lungs — Watches the Circula-
tion of the Blood —Observes the Malpighian Layer in the Human
Skin — Describes the structure of the Silkworm — Leeuwenhoeck
discovers Animalcules — Grew and Malpighi discover the Cellular
Structure of Plants — The Stomates in Leaves — They study the
Germination of Seeds — Ray and Willughby classify and describe
Animals and Plants — The Friendship of these two Men . • 137

CHAPTER XVIII.

SCIENCE OF THE SEVENTEENTH CENTURY (CONTINUED).

1642, Birth of Newton — His Education — 1666, His three great
Discoveries first occur to him — Method of Fluxions and Dif-
ferential Calculus — First Thought of the Theory of Gravitation
— Failure of his Results in consequence of the Faulty Measure-
ment of the size of the Earth — 1682, Hears of Picart's new
Measurement — Works out the result correctly, and proves the
Theory of Gravitation — Explanation of this Theory — Establishes
the Law that Attraction varies inversely as the squares of the
distance — 1687, Publishes the 'Principia' — Some of the Pro-
blems dealt with in this Work . . . . . . .147

CHAPTER XIX.

SCIENCE OF THE SEVENTEENTH CENTURY (CONTINUED)

Transits of Mercury and Venus — Kepler foretells their occurrence
— 163 1, Gassendi observes a Transit of Mercury — 1639, Hor-
rocks foretells and observes a Transit of Venus — 1676, Halley
sees a Transit of Mercury, and it suggests to him a method for
Measuring the Distance of the Sun — 1691-1716, Halley de-
scribes this method to the Royal Society — Explanation of
Halley's method 156

CONTENTS.

CHAPTER XX.
SCIENCE OF THE SEVENTEENTH CENTURY (CONTINUED).

PAGE

Newton's Discovery of the Dispersion of Light — Traces the
amount of Refraction of each of the Coloured Rays — Makes a
Rotating Disc turning the colours of the Spectrum into White
Light — Reason why all Light passing through glass is not
Coloured — Mr. Chester More Hall discovers the Difference of
Dispersive Power in Flint and Crown Glass — Newton's Papers
destroyed bvhis pet dog — Last years of Newton's life . .164

CHAPTER XXL

SCIENCE OF THE SEVENTEENTH CENTURY (CONTINUED).

Roemer measures the Velocity of Light — Newton's Corpuscular
Theory of Light — Undulatory or Wave Theory proposed by
Huyghens — Invention of Cycloidal Pendulums by Huyghens —
Discovery of Saturn's Ring — Sound caused by Vibration of Air —
Light by Vibration of Ether — Reasons why we see Light —
Reflection of Waves of Light — Cause of Colour — Refraction
explained by the Undulatory Theory — Mr. Tylor's Illustration
of Refraction — Double Refraction explained by Huyghens —
Polarisation of Light not understood till the nineteenth century . 1 72

CHAPTER XXIL

Summary of the Science of the Seventeenth Century . 182

CHAPTER XXin.

SCIENCE OF THE EIGHTEENTH CENTURY.

Great spread of Science in the Eighteenth Century — Advance of
the Sciences relating to Living Beings — Foundation of Leyden
University in 1574 — Boerhaave, Professor of Medicine at Ley-
den, 1 701 — Foundation of Organic Chemistry by Boerhaave —
Influence of Boerhaave upon the study of Medicine — Belief of
the Alchemists in ' Vital Fluids ' — Boerhaave's Experiments on
the Juices of Plants — Dr. Hales's Experiments on Plants — Boer-
haave's Analyses of Milk, Blood, &c. — Great popularity of his
Chemical Lectures , . . . . . . . .189

CONTENTS.

CHAPTER XXIV.

SCIENCE OF THE EIGHTEENTH CENTURY (CONTINUED).

PAGE

Childhood of Haller — Foundation of the University of Gottingen
in 1736 — Haller made Professor of Anatomy — Haller's Ana- ■
tomical Plates — He discovers the power of Contraction of the
Muscles — Rise of Comparative Anatomy — John Hunter's in-
dustry in Dissecting and Comparing the Structures of different
Animals — His Museum and the arrangement of his Collection —
Bonnet's Experiments on Plants — Experiments upon Animals by
Bonnet and Spallanzani — Regrowth of different parts when cut
off — Bonnet's theory of Gradual Development of Plants and
Animals — Anatomical Works of Haller — He discovers the
power of the Muscles to contract . . . . . -195

CHAPTER XXV.

SCIENCE OF THE EIGHTEENTH CENTURY (CONTINUED).

Birth and Early Life of Bufifon and Linnaeus compared — Bufifon's
Work on Natural History — Daubenton wrote the Anatomical
Part — Buffon's Books very interesting, but not always accurate —
He first worked out the Distribution of Animals — Struggles of
Linnaeus with Poverty — Mr. Clifford befriends him — He becomes
Professor at Upsala — He was the first to give Specific Names to
Animals and Plants — Explanation of his Descriptions of Plants
— Use of the Linnaean or Artificial System — Afterwards super-
seded by the Natural System — Linnaeus first used accurate terms
in describing Plants and Animals — Character of Linnaeus — Sale
of his Collection, and Chase by the Swedish Man-of-war . . 204

CHAPTER XXVL

SCIENCE OF THE EIGHTEENTH CENTURY (CONTINUED).

The Study of the Earth neglected during the Dark Ages — Preju-
dices concerning the Creation of the World — Attempts to Ac-
count for Buried Fossils — Palissy, the Potter, first asserted that
Fossil-shells were real Shells — Scilla's Work on the Shells of
Calabria, 1670 — Woodward's Description of Different Fonna-
tions, 1695 — Lazzaro Moro one of the first to give a true expla-

-^^iii CONTENTS.

PAGE

nation of the facts — Abraham Werner lectures on Mineralogy
and Geology, I775 — Disputes between the Neptunists and Vul-
canists — Dr. Hutton first teaches that it is by the Study of the
Present that we can understand the Past — Theory of Hutton —
Sir J. Hall's Experiments upon Melted Rocks — Hutton dis-
covers Granite Veins in Glen Tilt — William Smith, the * Father
of English Geologists ' — His Geological Map of England . . 214

CHAPTER XXVII.

SCIENCE OF THE EIGHTEENTH CENTURY (CONTINUED).

Birth of Modem Chemistry — Discovery of 'Fixed Air,' or Car-
bonic Acid, by Black and Bergmann — Working out of ' Che-
mical Affinity ' by Bergmann — He tests Mineral Waters, and
proves ' Fixed Air ' to be an Acid — Discovery of Hydrogen by
Cavendish — He investigates the Composition of Water — Oxygen
discovered by Priestley and Scheele — Priestley's Experiments —
He fails to see the true bearing of his Discovery — His Political
Troubles and Death — Nitrogen described by Dr. Rutherford —
Lavoisier lays the Foundation of Modern Chemistry — He
destroys the Theory of ' Phlogiston ' by proving that Combustion
and Respiration take up a Gas out of the Air — Discovers the
Composition of Carbonic Acid and the nature of the Diamond —
French School of Chemistry — Death of Lavoisier . . . 225

CHAPTER XXVIII.

SCIENCE OF THE EIGHTEENTH CENTURY (CONTINUED).

Doctrine of Latent Heat, taught by Dr. Black in 1760 — Water
containing Ice remains always at 0° C, and Boiling Water at
100° C, however much Heat is added — Black showed that the
lost Heat is absorbed in altering the condition of the Water —
Watt's Application of the Theory of Latent Heat to the Steam-
engine — Early History of Steam-engines — Newcomen's Engine
— Watt invents the Separate Condenser — Diagram of Watt's
Engine — Difficulties of Watt and Boulton in introducing Steam-
engines ........... 241

CONTENTS. xLc

CHAPTER XXIX..

SCIENCE OF THE EIGHTEENTH CENTURY (CONTINUED).

PAGE

Benjamin Franklin, born 1706 — His Early Life — Du Faye dis-
covers two kinds of Electricity — Franklin proves that Electricity
exists in all Bodies, and is only developed by Friction — Positive
and Negative Electricity — Franklin draws down Electricity from
the Sky — Invents Lightning-conductors — Discovery of Animal
Electricity by Galvani — Controversy between Galvani and Volta
— Volta proves that Electricity can be produced by the Contact
of two Metals — Electrical Batteries — The Crown of Cups — The
Voltaic Pile .......... 253

CHAPTER XXX.

SCIENCE OF THE EIGHTEENTH CENTURY (CONTINUED).

Bradley and Delisle, Astronomers — Aberration of the Fixed Stains
— Nutation of the Axis of the Earth, Delisle's Method of Mea-
suring the Transit of Venus — Lagrange and Laplace — Libration
of the Moon accounted for by Lagrange — Laplace works out the
Long Inequality of Jupiter and Saturn — Lagrange proves the
Stabihty of the Orbits of the Planets — Sir William Herschel
constructs his own Telescopes — Discovery of a New Planet — •
Discovery of Binary Stars — Herschel studies Star-clusters and
Nebulae — Theory of Nebulae being matter out of which Stars
are made — The Motion of our Solar System through Space —
Weight of the Earth determined by the Schehallien Experiment
— Summary of the Science of the Eighteenth Century . . 265

CHAPTER XXXI.

SCIENCE OF THE NINETEENTH CENTURY.

Difficulties of Contemporary History— ^.Discovery of Asteroids and
Minor Planets between Mars and Jupiter — Dr. Gibers suggests
they may be fragments of a larger Planet — Encke's Comet, and
the correction of the size of Jupiter and Mercury — Biela's
Comet, noticed in 1826 — It divides into two Comets in 1845 —

CONTENTS.

PAGE

Irregular movements of Uranus — Adams and Leverrier calculate
the position of an Unknown Planet — Neptune found by these
calculations in 1846 —A Survey of the whole Heavens made by
Sir John Herschel — His work in Astronomy — Comets and
Meteor-systems ......... 287

CHAPTER XXXII.

SCIENCE OF THE NINETEENTH CENTURY (CONTINUED).

Discoveries concerning Light made in the Nineteenth Century —
Birth and History of Dr. Young — He explains the Interference
of Light — Cause of Prismatic Colours in a Shadow — And in a
Soap-bubble — Malus discovers the Polarisation of Light caused
by Reflection — Birth and History of Fresnel — Polarisation of
Light explained by Young and Fresnel — Complex Vibrations of
a Ray of Light — How these Waves are reduced to two separate
Planes in passing through Iceland-spar — Sir Da,vid Brewster
and M. Biot explain. the colours produced by Polarisation . . 302

CHAPTER XXXIII.

SCIENCE OF THE NINETEENTH CENTURY (CONTINUED).

History of Spectrum Analysis — Discovery of Heat-rays by Sir W.
Herschel — And of Chemical Rays by Ritter of Jena — Photo-
graphy first suggested by Davy and Wedgwood — Carried out by
Daguerre and Talbot — Dark Lines in the Spectrum first ob-
served by WoUaston — Mapped by Fraunhofer — Life of Fraun-
hofer — He discovers that the Dark Lines are different in Sun-
light and Star-light — Experiments on the Spectra of different
Flames — Four new Metals discovered by Spectrum Analysis —
Artificial Dark Lines produced in the Spectrum by Sir David
Brewster — Bunsen and Kirchhofif explain the Dark Lines in the
Solar Spectrum — Metals in the Atmosphere of the Sun — Huggins
and Miller examine the Stars and Nebulae by Spectrum Analysis . 3 r5

CONTENTS.

CHAPTER XXXIV.

SCIENCE OF THE NINETEENTH CENTURY (CONTINUED).

PAGE

Early Theories about Heat — Count Rumford shows that Heat can
be produced by Friction — He makes Water boil by boring a
Cannon — Davy makes two pieces of Ice melt by Friction — His
conclusion about Heat— How 'Latent Heat' is explained on
the theory that Heat is a kind of Motion — Dr. Mayer suggests
the Determination of the Mechanical Equivalent of Heat — Dr.
Joule's Experiments on the conversion of Motion into Heat — Dr.
Him's Experiments on the conversion of Heat into Motion — Proof
of the Indestructibility of Force and Conservation of Energy . 329

CHAPTER XXXV.

SCIENCE OF THE NINETEENTH CENTURY ^CONTINUED).

Oersted discovers the Effect of Electricity upon a Magnet — Electro-
Magnetism — Experiments by Ampere on Magnetic and Electric
Currents — Ampere's Early Life — Direction of the North Pole of
the Magnet depends on the course of the Electric Currents —
Magnetic Currents set up between two Electric Wires — Electro-
Magnets made by means of an Electric Current — Arago magne-
tises a Steel Bar with an ordinary Electrical Machine — Faraday
discovers the Rotatory Movement of Magnets and Electrified
Wires — Produces an Electric Current by means of a Magnet —
Seebeck discovers Thermo-Electricity, or the production of Elec-
tricity by Heat — Schwabe discovers Periodicity of the Spots on
the Sun — Sabine suggests a connection between Sun-spots and
Magnetic Currents — This proved in 1859 by Observations of
Carrington and Hodgson — Electric Telegraph— Wheatstone —
Cooke — Steinheil — Morse — Bain ...... 34.1

CHAPTER XXXVI.

SCIENCE OF THE NINETEENTH CENTURY (CONTINUED/.

Davy discovers that Nitrous Oxide produces Insensibility — Laugh-
ing-gas— Safety-lamp, 18 15 — Nicholson and Carlisle discover
Decomposition of Water, 1800 — Davy discovers the effect of
Electricity upon Chemical Affinity — Faraday's Discoveries in

xxii CONTENTS.

FAGS

Electrolysis — Indestructibility of Force — Various Modes dis-
covered of Decomposing Substances — ^John Dalton, chemist —
Law of Definite Proportions — Law of Multiple Proportions —
Dalton's Atomic Theory — The Study of Organic Chemistry —
Liebig, the great teacher in Organic Chemistry . . . 362

CHAPTER XXXVn.

SCIENCE OF THE NINETEENTH CENTURY (CONTINUED).

The Organic Sciences are too difficult to follow out in detail — .
Jussieii's Natural System of Plants — Goethe proves the Meta-
morphosis of Plants — Humboldt studies the Lines of Average
Temperature on the Globe — Extends our knowledge of Physical
Geography — Writes the ' Cosmos ' — Death of Humboldt in
1858 380

CHAPTER XXXVin.

SCIENCE OF THE NINETEENTH CENTURY (CONTINUED).

The three Natui'alists, Lamarck, Cuvier, and Geoffroy St.-Hilaire
— Cuvier begins the Museum of Comparative Anatomy — La-
marck's History of Invertebrate Animals — G. St.-Hilaire brings
Natural History Collections from Egypt — Lamarck on the
Development of Animals — G. St.-Hilaire on 'Homology,' or
the similarity in the parts of different animals — Cuvier's ' Regne
Animal ' and his Classification of Animals — Cuvier on the Per-
fect Agreement between the Different Parts of an animal — He
Studies and Restores the Remains of Fossil Animals — His
' Ossemens Fossiles ' — Death of Cuvier — Von Baer on the Study
of Embryology — His History of the Development of Animals,
1828 388

CHAPTER XXXIX.

SCIENCE OF THE NINETEENTH CENTURY (CONTINUED).

Prejudices which retarded the study of Geology — Sir Charles
Lyell traces out the Changes going on now — Mud carried down
by the Ganges — Eating away of Sea-coasts — Eruption of Skap-
tar Jokul — Earthquake of Calabria — Rise and Fall of Land —

CONTENTS.

PAGE

•Principles of Geology' published in 1830 — Louis Agassiz: his
early life — De Saussure's Study of Glaciers — Agassiz on Europe
and North America being once covered with Ice — Boucher de
Perthes on Ancient Flint Implements — McEnery on Flint Im-
plements in Kent's Cavern, v^dth Bones of Extinct Animals —
Swiss Lake-dwellings — ' Antiquity of Man ' .... 404

CHAPTER XL.

SCIENCE OF THE NINETEENTH CENTURY (CONTINUED).

Facts which led Naturalists to believe that the different kinds of
Animals are descended from Common Ancestors — All Animals of
each class formed on one Plan — Embryological Structure —
Living and Fossil Animals of a country resemble each other —
Gradual Succession of Animals on the Globe — Links between
different species — Darwin's Theory of Natural Selection —
Wallace worked out the same Theory independently — Sketch of
the Theory of Natural Selection — Selection of Animals by Man —
Selection by Natural Causes — Difficulties in Natural History
which are explained by this Theory — Foolish Prejudices against
it — Concluding Remarks on the History of Science . . -4^9

A SHORT HISTORY

OF

NATURAL SCIENCE.

INTRODUCTION.

As THIS little work is to be a history of Natural Science,
it will be as well to begin by trying to understand what
Science is.

The word itself comes from scio^ I know, and means
simply knowledge. The science of botany is therefore the
knowledge of plants ; and the science of astronomy, the know-
ledge of the heavenly bodies.

But now comes the question, What kind of knowledge is
required ? You might be able to tell the names of all the
plants in the world, and of all the stars in the sky, and yet
have scarcely any real knowledge of botany or astronomy.
You will easily understand this if we compare it with some-
thing you meet with in daily life. Suppose I took you into
a large school and told you the names of all the children
there ; even if you learnt these names by heart, you could
not say you knew the children, or anything about them,
beyond their names. One might be ill-tempered, another
good-tempered ; one might have a home and a father and
2

HISTORY OF SCIENCE.

mother, another might be an orphan and homeless, and you
would find their mere names of no use to you if you wished
to choose one of them to do any work, or to be your friend
and companion. For this you would want to learn their
character, their habits, and other real facts about them.

Now this last is just the kind of knowledge which is
required in science. If, besides the name of a plant, you
know its different parts, the shape of its leaves, the number
of its seeds, and how they are arranged in the seed-vessel,
the number of stamens or thread-like bodies in the middle
of the flower, the number and colour of its petals or flower-
leaves, and many other points like these, then you know
something of structural botany. If you know, besides, how
a plant takes up food, how it breathes, and how the sunlight
acts upon the leaves and alters the juices of the plant, then
you know something of the life of the plant, ox physiological
botany. If you know where the plant grows best, in what
soil, in what climate, and in what countries, then you know
something oi geographical botany ; and if your knowledge is
accurate and carefully learnt it is real science.

By this you will see that science means not merely know-
ledge, but an accurate and clear knowledge about the things
which we see around us in the universe. In the present day,
people are beginning to teach children much more on these
subjects than they did forty years ago, and every intelligent
boy or girl probably knows that Astronomy is the science of
the sun, stars, and planets; Physics and Mechanics^ the
sciences which teach the properties of bodies and their laws
of motion ; Biology the science of life ; Geology the science
of the earth, teaching us how the different rocks have been
formed ; and Chemistry the science which treats of the
materials of which all substances are made, and shows the

IJ^TROD UCTION.

changes which take place when two substances act upon one
another so as to make a new substance.

There are many simple books written now to explain
these sciences, and those who wish can read these books and
study the examples and experiments given in them. They
tell us what science now is, and the explanations given by
the best men about the universe in which we live. But they
do not tell us how science has become what it is, and it is this
which I hope to tell you in the present book.

A man who wishes to understand a steam-engine can do
so by going to an engineer and having each part explained
to him j but if he wishes to know the history of the steam-
engine he must go back to the first one ever made, and
study each new improvement as it arose. And so if we go
back to the first attempts made by thoughtful men to under-
stand nature, and then trace up step by step the knowledge
gained from century to century, we shall have at least a mere
intelligent understanding of that which is taught us now.
But if we have any true love of knowledge we shall gain far
more than this ; for in studying the history of those grand
and patient men who often spent their lives and made great
sacrifices to understand the works of God, the merest child
must feel how noble it is to long and strive after truth.

When we go back to very early ages we do not find that
people understood much of what we now call science. So
long as men were chiefly occupied in protecting themselves
against other savage men and wild beasts, and had to
struggle very hard to get food and clothing, they had very
little time or wish to study nature. Still they learnt many
things which were necessary for their life. They learnt, for
instance, at what times the sun rose and set, for upon this

HISTORY OF SCIENCE.

their day's work depended. They learnt at what time in the
month the moon was full, so that they could see their way
by moonlight ; and they remarked very early the times when
spring, summer, autumn, and winter came round, because
the sowing of their seeds and the gathering of their fruits
depended upon these seasons.

In this way we find that as far back as history goes men
have always had some knowledge of the facts of nature ; and
those nations, hke the Egyptians and Chinese, which long
ago had become highly civilized, had learnt a very great
deal, and must probably have known some things of which
we are still ignorant.

There has been a great deal written about the science of
the Chinese, Indians, and Egyptians, but I shall not tell you
anything about them here, because their knowledge has had
very little to do with the science which has come down to
us, and it would besides be difficult to give you any real idea
of what they knew without writing a book on the subject.

We will start, therefore, with the Greeks, at the time when
they first began to try and explain some of the natural
events which they saw taking place every day. This was
about the year 700 B.C., when Thales, one of the seven wise
men, was living, and you will see in the next chapter that
even at this time, when Greece was famous for its learning,
the people had still some very strange ideas about the
working of the universe.

PART I.
SCIENCE OF THE GREEKS

FROM B.C. 639 TO A.D. 200

Chief Men of Science among the Greeks^

e

B.C.

Thales .

About 640.

Anaximander

. 610,

Pythagoras .

500.

Anaxagoras .

499-

Democritas .

• 459.

Hippocrates ,

. 420.

Eudoxus

, 406.

Aristotle

■ 384.

Theophrastus

37t-

Aristarchus .

350^

Euclid .

300.

Archimedes .

287.

Erasi stratus .

?

Herophilus .

?

Eratosthenes

276.

Hipparchus .

160.

Strabo .

50 to A.D. 18.

Ptolemy

. 70.

Galen .

. 131'

CH. I. SCIENCE OF THE GREEKS.

CHAPTER I.

639 TO 470 B.C.

Ignorance of the Greeks concerning Nature — Ionian School of Learning
— Thales discovers the Solstices and Equinoxes, and knows that the
Moon Reflects the Light of the Sun — Anaximander invents a Sun-
dial— Discovers the Phases of the Moon^-Makes a Map of the
Ancient World — Pythagoras teaches that the Earth moves, and- that
the Morning and Evening Star are the same — He studies Geology,
and knows that Land has in some places become Sea — True sayings
of Pythagoras and his Followers about Geology.

About 600 years before Christ was born, the Greeks were
the most learned people in Europe. They were naturally a
handsome and clever race, and their young men were
trained to be both good soldiers and good scholars. An
English boy, if he could be carried back to those days,
would find that the young Greeks could read, write, draw,
and argue as well as himself, and probably that they could
leap, wrestle, and run far better than himself or any of his
schoolfellows.

But on some points he would find that their ideas were
very strange. If he spoke to them of the woiid as a round
globe they would stare in astonishment, and tell him that
such an idea was absurd, for everyone knew that the world
was flat with the sea flowing all round it. If he asked them,
in his turn, about Mount Etna, they would surprise him by
replying that the god Vulcan had his smithy underneath the
mountain, where he was forging thunderbolts for Jove, and

SCIENCE OF THE GREEKS. pt. i.

that Etna was the chimney of his forge. But if he spoke of
the sun as a globe of Hght, they would turn away from him
in horror as a wicked unbeliever in the gods, for who among
the Greeks did not know that the sun was the god Apollo,
who drove his chariot every day across the sky from east to
west ? In fact, the Greeks, though learned and brave, were
quite ignorant of what we now call ' natural knowledge ; '
they did not know that the rising and setting of the sun,
and the eruption of a volcano, are things which happen from
natural causes ; but everything which was not done by man,
they thought was the work of invisible beings or gods.

It was not long, however, before some wise men began
to think more deeply about these things. You will have
read in Grecian history how the Greeks, after the taking of
Troy, crossed over the Hellespont and founded colonies on
the coast of Asia Minor ; one of the largest of these colonies
was called Ionia, and the lonians became famous for their
learning and wisdom.

Thales, 640. — Here Thales, one of the seven wise men
of Greece, was born at Miletus, about 640 B.C. Thales
travelled in Egypt, and learned many things from the
Egyptians, and then returned to his own land and founded
a school of learning. He was the first Greek who studied
astronomy, and although, like his countrjnnen, he believed
that the earth was flat and floated on the water, yet he made
several great discoveries.

The Greeks had always divided their year into two parts
only, summer and winter, but Thales discovered that there
are four distinct divisions marked out by the sun. He
noticed that in the middle of winter the sun, instead of
passing overhead, reached at mid-day only a certain low
point in the heavens, and then began to set again, so that

CH. I. THALES—ANAXIMANDER, 9

the day was short and the night long. This went on for a
few days, and because the sun stood at the same height
every day, the name of winter solstice^ or sun-standing, was
given to these days in the middle of winter. Afterwards the
sun began to rise a very little higher every day, till in three
months, when winter had passed away and the plants and
trees began to bud, the sun took exactly twelve hoiurs to pass
across the sky from sunrise to sunset, so then the day was
twelve hours long, and the night also twelve hours ; this was
called the spring equi-nox^ or equal night, meaning that the
day and night were of equal length. After this the sun still
rose higher every day, and in three months more stood for
some days nearly overhead at mid-day, thus making a long
journey from sunrise to sunset, and causing the day to be
long and the night short. This was- the summer solstice.
Then the sun began to rise less high every day, and in
another three months there was again equal day and equal
night — the autumn equinox had arrived. Finally, in another
three months, the shortest day arrived again, and the whole
round began afresh. This was how Thales marked out the
solstices and the equinoxes ; we still call them by the same
name as he did, and you may watch these changes of the
sun in the sky for yourself.

Thales knew that the sun and stars were not gods, and
thought they were made of some fiery substance ; he knew
also that the moon receives its light from the sun and reflects
it like a looking-glass. He was very learned in mathematics,
and invented several problems now found in the ' Elements
of Euclid.' He is also said to have foretold an eclipse, but
this is probably not true, as it requires more knowledge than
he is likely to have had.

Anaximander of Miletus, 610 b.c, the friend of Thales,

lo SCIENCE OF THE GREEKS. ft. I.

was the next Greek who made some important discoveries in
science. He invented a sun-dial, by making a flat metal
plate with the hours of the day marked upon it in a certain
order, so that a large pin, or style as it is called, standing in
the middle of the plate, cast a shadow on the right hour
whenever the sun shone upon it. You can understand that
as the sun is low down in the morning and gradually passes
overhead during the day, it will cause the pin to throw its
shadow in a different direction at different hours.

In this way Anaximander taught the Greeks to measure
the time of day. He is also said to have been the first as-
tronomer who understood why we see the bright face of the
moon growing from a crescent to a full moon and then di-
minishing again. To know this he must also have known
that the moon moves round the earth every month. You can
imitate the changes of the moon if you take a round stone
and hold it just above your head between you and the suH;
you will then have its shady side towards you; pass it slowly
round your head, you will find that you see first a bright edge
appearing, then more and more of the bright side, till when
the stone is on one side of your head and the sun the other,
you will see the whole of one side of the stone reflecting the
sun's light — this is a full moon. Pass it on slowly round, and
you will see this bright side disappear gradually till you
bring it back to its old position between you and the sun,
when it will be again dark. This is what the moon does
every month, producing what are called the phases of the
moo7i. Anaximander also made a map of the world, or at
least of as much of it as was known in his time.

Pythagoras, one of the most celebrated of the learned
men of Greece, is the next who tells us anything about science.
The time and place of his birth is uncertain, but he lived

CH. I. • PYTHAGORAS ON GEOLOGY. ii

somewhere between 566 and 470 B.C. He travelled in
Egypt, and learnt much there, and afterwards settled at Ta-
rentum, in Italy, where he founded a famous sect called the
Pythagoreans. You will read of the opinions of Pythagoras
in books of philosophy, but we are only concerned with what
he taught about nature.

He was the first to assert that the earth was not fixed,
but moved in the heavens, but he did not know that it
m'oves round the sun. He also discovered that the evening
and morning star are the same planet; he called this planet
Eosphorus, for it did not receive the name of Venus till some
time afterwards.

Some of the most remarkable truths taught by Pytha-*
goras were about geology, or the study of the earth. He
noticed that seashells were sometimes to be found far inland
imbedded in solid ground in a way that showed they were
not brought there by man. Therefore, he argued that to
bury j<?<z-shells in the rocks, the sea must once have been
there. He had also probably watched the sea eating away
the cliffs on the shores of Italy, as you may see it doing
now on the shores of Norfolk and Suffolk ; and when he
was in Egypt he must have seen the Nile carrying mud and
laying it down at its mouth, or delta, to form new land. From
all these and other observations he, and his pupils who fol-
lowed him, drew some very true conclusions w^hich are given
in Ovid's '■ Metamorphoses' : —

1. Solid land has been converted into sea.

2. Sea has been changed into land. Marine shells lie
far distant from the deep.

3. Valleys have been excavated by running water, and
floods have washed down hills into the sea.

4. Islands have been joined to the mainland by the

12 SCIENCE OF THE GREEKS, pt. i.

growth of deltas and new deposits, as in the case of Antissa
joined to Lesbos, Pharos to Egypt, &c.

5. Peninsulas have been divided from the mainland and
have become islands, as Leucadia ; and according to tradi -
tion Sicily, the sea having carried away the isthmus.

6. Land has been submerged by earthquakes ; the Gre-
cian cities of Helice and Buris, for example, are to be seen
under the sea, with their walls inclined.

7. There are streams which have a petrifying power, and
convert the substances which they touch into marble.

8. Volcanic vents shift their position ; there was a time
when Etna was not a burning mountain, and the time will
come when it will cease to burn.

These, and other sentences of the same kind, show how
carefully Pythagoras and his followers must have observed
nature, for the changes that are going on upon the earth take
place so very slowly that it is only by very careful comparison
that we can prove they are happening at all. Pythagoras
was the first man who was called z. philosopher, or lover of
wisdom. He made many discoveries about musical notes,
and succeeded in stretching strings so that when struck they
gave the right notes of the octave in succession.

CH. II. ANAXAGORAS STUDIES THE MOOJST. 13

CHAPTER II.

499 TO 322 B.C.

Anaxagoras studies the Moon — Describes Eclipses of the Sun and
Moon — Is Tried and Condemned for Denying that the Sun is a
God — Hippocrates the Father of Medicine — Separates the Office of
Priest and Doctor — Studies the Human Body — Eudoxus has an
Observatory — Makes a Map of the Stars — Explains the Movements
of the Planets — Democritus Studies the Milky Way — Aristotle an
Astronomer and Zoologist — Divides Animals into Classes — Teaches ■
that there is a Gradual Succession of Animal Life — Studies the
Difference of the Life in Plants and Animals.

Anaxagoras, who was the next great teacher after Pythagoras,
was bom in Ionia about 499 B.C., but he went when quite
young to Athens. He loved to study nature for its own
sake, and was once heard to say that he was bom to con-
template the sun, moon, and heavens. Although there were
no telescopes in those days, he managed to observe that
there were mountains, plains, and valleys in the moon. He
believed it to be a second earth, perhaps with living beings
in it. He did not know, as we do now, that the moon has
no atmosphere round it, such as living beings like ourselves
require in order to breathe. He discovered that an eclipse
of the sun is caused by the moon coming directly between
the earth and the sun, and an eclipse of the moon by the
earth coming between the moon and the sun. "When the
moon comes exactly between our earth and the sun, we
see the moon's dark body pass over the sun, so as to

14 SCIENCE OF THE GREEKS. PT. T.

eclipse or shut it out; and when our earth comes exactly
between the moon and the sun we cut off the sun's hght
from the moon, and see our own shadow passing over the
moon's face, and thus we ecUpse the moon.

Anaxagoras knew that the planets Jupiter, Saturn, Venus,
Mars, and Mercury move in the heavens, and that the stars
do not move. He believed that all the heavenly bodies
were fiery stones ; the sun he thought was a huge fiery stone
as big as the Peloponnesus. He was the first scientific man
who was persecuted for declaring boldly what he believed
to be the truth. The Greeks were very angry with him for
teaching that the sun was not a god; so he was tried at
Athens, when quite an old man, and condemned to death.
His friend Pericles pleaded for him, and the sentence was
changed to a fine and banishment, and he retired to Lamp-
sacus, where he went on teaching science and philosophy
till his death.

Anaxagoras was the first Greek philosopher who taught
that there must be one Great Intelligence ruling over the
universe. So that the Greeks punished as an atheist the
man who first taught them of a Supreme God. This ex-
ample should teach us to be very careful how we condemn
the opinions of others, for fear that we, like the Greeks,
should think another wicked only because his thoughts are
nobler than we can understand.

Hippocrates, 420. — While Anaxagoras was studying the
heavens, another man, born about 420 B.C. in the little
island of Cos, was studying men, and how to make their
lives healthier and happier. Hippocrates, the Father of
Medicine, belonged to a family of doctors and priests.
The Greeks did not understand that illness comes to us
because we do not know how to take care of our bodies.

CH. II. HIPPOCRATES— ARISTOTLE. 15

They thought that every illness was a punishment sent be-
cause one of their gods was angry, so when they were ill
they sent a present to the temple of ^sculapius, the god of
medicine, and then went to the priests of ^sculapius to
cure them. The ancestors of Hippocrates were all priests of
^sculapius, but he separated himself from the priesthood
and devoted his time to studying the human body, and find-
ing out the causes of disease. He studied the effect that
heat and cold have upon us, and taught physicians to pay
attention to the kind of food given to sick people, and espe-
cially to watch carefully in sickness for the critical point
when the fever is at its height. He wrote many learned
works on the human body, and you should remember his
name as the Founder of the science of Medicine.

Eudoxus, 406 — Democritus, 459. — The next great astro-
nomer after Anaxagoras was called Eudoxus. He was born
about 406 B.C., at Cnidos, in Asia Minor, where he had an
observatory, from which he could watch the heavens, and
by this means he made a map of all the stars then known.
He was the first Greek astronomer who explained how the
planets Jupiter, &c., moved round in the heavens, and the
time at which they would appear again exactly in the same
place as before. The great philosopher Democritus, of
Abdera (459 B.C.), who lived about the same time as
Eudoxus, made the remarkable guess that the beautiful
bright band called the 'Milky Way,' which stretches every
evening right across the sky, is composed of millions of
stars scattered like dust over the heavens.

Aristotle, io8^ one of the most famous philosophers of
Greece, was also a great student of nature. He was bom at
Stagira, in Thrace, 384 B.C., but studied at Athens under
Plato, and afterwards became the tutor of Alexander the

i6 SCIENCE OF THE GREEKS. PT. I.

Great. Aristotle did much for astronomy, by collecting and
comparing the discoveries of the astronomers who came
before him. He is the first of the Greek writers who states
very decidedly that the earth must be a round globe, and
he discovered an eclipse, or occultation as it is termed by
astronomers, of the planet Mars by the moon.

But the best scientific work of Aristotle was his study of
animals. He persuaded Alexander the Great, who governed
Greece at that time, to employ several thousand people to
collect specimens of animals in all parts of Europe and Asia
and to send them to Athens. Here Aristotle examined
them and arranged them under difierent classes according
to their organs, or difi"erent parts of their body, and the man-
ner in which they used them. Many of Aristotle's divisions
of the animal kingdom are still in use, and he may fairly be
called the Founder of Zoology. He pointed out that we can
trace an unbroken chain from the lowest plant up to the
highest animal, each group being only divided from the
next by very slight difierences ; nor can we tell, he said,
where plants end and animals begin, for there are some
forms which are so Hke both plants and animals that we
cannot decide in which division to place them.

He also pointed out that the life in plants is much lower
than in animals, for if you cut a plant into pieces, each piece
will grow, showing that the parts of a plant are simple and
do not depend very closely upon each other. But an ani-
mal, and especially one of the higher animals, is a most
complicated piece of machinery. If you hurt or destroy any
of the most important parts the whole body dies, and if you
cut off any part whatever, that part dies as soon as it is se-
parated from the rest. These and many other very interest-
ing facts about animals are to be found in Aristotle's great

CH. II. THEOPHRASTUS THE FIRST BOTANIST. 17

work on Natural History, which, however, you must remem-
ber, was only one out of many great works written by him on
subjects which do not concern us here.

Theophrastus, 371. — Among the pupils of Aristotle was
a man named Theophrastus, who was born at Eresus, 371
B.C. Theophrastus devoted himself chiefly to the study of
plants, and is the first botanist whose name has been handed
down to us. The Greel?:s understood very little about
plants except those which they used for medicine ; but Theo-
phrastus described about 500 different kinds of plants, and
divided them into trees, herbs, and shrubs. We know, how-
ever, very little about his writings.

1 8 SCIENCE OF THE GREEKS, FT. I.

CHAPTER IIL

320 to 212 B.C.

School of Science at Alexandria — The Ecliptic and the Zodiac — Greeks
believed that the Sun moved round the Earth — Aristarchus knew
that it was the Earth which moved — He also knew of the Obliquity
of the Ecliptic, and that the Seasons are caused by it — He knew
that the Earth turns daily on its Axis — Euclid discovers that Light
travels in straight lines — Archimedes discovers the Lever —
Principle of the Lever — Hiero's Crown, and how Archimedes dis-
covered the principle of Specific Gravity.

While Aristotle was studying science at Athens, the Greeks
under Alexander the Great were making great conquests in
Egypt, where Alexander founded a city bearing his own
name on the shores of the Mediterranean. After Alexan-
der's death this city, called Alexandria, fell to the portion of
Ptolemy Lagus, one of Alexander's generals, who was suc-
ceeded by a number of princes of the same name. The
Ptolemies were all patrons of learning and science, and the
school of Alexandria became one of the most famous the
world has ever known. By this time the Greeks had learnt
many astronomical facts, some of them probably from the
Egyptians. They had traced the ecliptic, or the sun's appa-
rent yearly path through the heavens, and, dividing this path
into twelve parts, they called each division by the name of a
constellation or cluster of stars. These constellations re-
ceived most of them the names of animals, and therefore
the circle of the twelve constellations was called the Zodiac^

CH. III. SIGNS OF THE ZODIAC. 19

or circle of animals. The names of the twelve signs are ;
I. Aries J the Ram; 2. Taio'us, the Bull; 3. Gemini, the
Twins j 4. Cancer, the Crab ; 5. Leo, the Lion ; 6. Virgo,
the Virgin ; 7. Libra, the Balance ; 8. Scorpio, the Scorpion;
9. Sagittarius, the Archer; 10. Capricornus, \he. Goat; 11.
Aquarius, the Water-bearer ; 12. Pisces, the Fishes.

It was by no means an easy thing to trace the sun's path
among the stars, because the sun and the stars are never in
sight at the same time, so they were obliged to notice the
constellations as they appeared close to the sun after he sank
at night or before he rose in the morning. These, they found,
varied a little each night, till when a whole year had passed
away, all the twelve signs had been in turn close to the sun, and
the round began again. Thus they learnt that the sun passed
over each of the twelve signs in the course of the year ; and
they thought from this that the sun travelled round the sky
while the earth stood still in the middle. We know now
that it is the sun which stands still in the middle while the
earth moves round, and it is worth while to make an experi-
ment to see how the Greeks were deceived.

Put twelve chairs round in a circle to represent the
signs of the Zodiac, and put yourself in the middle for a
person standing on the earth. Then swing a ball round you
just on a level with the chairs. You will see that the ball
passes between you and each chair as it makes a circle round
you. The Greeks believed . that the sun moved round in
this way between us and the stars. But now to represent
what really takes place, change places with the ball. Hang
the ball (the sun) up in the middle just on a level with the
chairs, and walk round it. Keep your eye fixed on the ball,
and you will see it will pass between you and each chair,
just as it did before. The effect is the same, though it is

20 SCIENCE OF THE GREEKS, pt. i.

you who are moving this time and not the ball. Thus the
Greeks made the same mistake which a child does in a rail-
way train when he thinks the houses and trees are flying
past, while it is he himself who is moving.

Aristarchus. — There was, however, one Greek astrono-
mer named Aristarchus, who discovered the real movement
as we know it now. Aristarchus was bom in Samos, some
time in the third century before Christ, but he came to
Alexandria, and was tutor to the sons of one of the Ptolemies.
He taught that the sun was immovable like the fixed stars,
and that it was the earth which travelled round the ecliptic.
He knew also that our earth does not stand quite upright in
its journey round the sun, but that a line drawn through the
earth from the north to the south pole would be sloping or
oblique to the ecliptic, and that this obliquity is the. cause of
our four seasons.

If you do not understand this you can work it out with
your ball, using a lamp to represent the sun. First draw an
ink-line round the middle of your ball for the equator, then
put your finger and thumb at the two ends of the ball to re-
present the two poles. Do not hold the ball upright, but
bring your thumb nearer to you than your finger. A line
drawn through the ball from your finger to your thumb will
now be inclined, and will represent the inclined axis of the
earth. Now look at the light and shade on the ball : the
north pole, which is turned towards the lamp, will be in full
light, and will have the long days of summer j the south pole
turned towards you will be in the dark, enduring its long
winter night Pass the ball on to your right, and when you
have gone round a quarter of a circle the poles will both
have equal light, and the southern spring and northern
autumn have arrived. Pass on again, and at the next quarter

CH. III. ARISTARCHUS AND EUCLID. 21

the south pole will be in summer and the north pole in
winter, while at the fourth and last point you have the
northern spring and the southern autumn. This was what
Aristarchus discovered, namely, that the changing seasons
are entirely caused by the earth having its axis (or the line
from pole to pole) oblique to its path round the sun, called
the ecliptic. This is called the obliquity of the ecliptic.

Aristarchus appears also to have been the first Greek
who understood that day and night were caused by the
earth turning round on its axis every day. If the Greeks
had understood his teaching, especially about the earth
moving round the sun, they would have made much more
progress in astronomy. But no one believed him, and more
than 1700 years passed away before Copernicus, of whom
you will read in chapter ix., discovered this great truth over
again. This Greek theory of the earth moving round the
sun is often called the Pythagorean system^ for it was thought
that Pythagoras taught it; but we have seen that, though
Pythagoras knew that the earth moves, he did not believe
that it went round the sun.

Euclid, 300. We must not pass through the third
century before Christ without mentioning Euclid, the great
mathematician and geometer, who collected together the
problems in the ' Elements of Euclid,' known to every
schoolboy. He was born at Alexandria about 300 B.C.
His works are too difficult for us to examine, and the only
discovery of his we can mention is, that light travels in
straight lines called ^ rays.' Thus, if you look at a sunbeam
shining across a dusty room, you can see the light reflected
in a straight line along the particles of dust, and if you let
sunHght through a hole in the shutter into a dark room, it
will light up a spot on the wall or floor exactly opposite to

22 SCIENCE OF THE GREEKS. PT. I.

the sun — the middle of the sun, the middle of the hole in the
shutter, and the middle of the spot of light, will all be in a
straight line.

Archimedes, 287. — Another famous geometer, Archi-
medes of Syracuse, bom 287 B.C., lived about the same
time as Euclid. He studied for many years at Alexan-
dria, but afterwards returned to his native country. One
of the greatest discoveries made by Archimedes was that
of a lever. If you place a book upright on the table
and lay a ruler or any flat piece of wood or metal across
it, you will find there is one point at which the ruler will
balance. .When you have balanced it, put an ounce weight
on each end and it will still balance at the same point,
which is called the fulcrum. But now change the ounce
at one end for a weight of two ounces ; that end will sink
at once, and to make it balance you will have to shift the
ruler and make the light end twice as long, because the
heavy end has twice the weight upon it. Put a three ounce,
and you must again lengthen the light end to three times the
length of the heavy one. You may go on doing this till the
heavy end is quite close to \k\& fulcrum or resting-point of the
ruler, and still the light weight will balance the heavy one.

This is the principle of the lever, and it is of great use in
lif tmg weights. A heavy block of stone which no set of men
could lift by taking hold of it may be easily raised by
fastening it to the short end of a lever, and then the weight
of the men at the end of the long arm will balance it, as the
one-ounce weight balances the four-ounce. Archimedes was
so delighted when he made this discovery that he is said to
have exclaimed : ' Give me a place on which to stand, and I
will raise the world.'

Another remarkable discovery made by Archimedes con'

CH. III. HIERO'S CROWN. 23

cerns the weight of bodies immersed in water. Hiero, king
of Syracuse, had given a lump of gold to be made into a
crown, and when it came back he suspected that the workmen
had kept back some of the gold and had made up the weight
by adding more than the right quantity of silver; but he had
no means of proving this, because they had made it weigh
as much as if it had been pure gold. Archimedes, puzzling
over this problem, went to his bath, which was filled to the
brim with water. As he stepped in he saw the water, which
his body displaced, pouring over the edge of the bath, and
to the astonishment of his servants he sprang out of the water
and ran home through the streets of Syracuse almost naked,
crying Eureka ! Eureka ! {' I have found it, I have found it.')
What had he found? He had discovered that any
solid body put into a vessel of water displaces its own bulk
of water, and therefore, if the sides of the vessel are high
enough to prevent it running over, the water will rise to a
certain height. He now got one ball of gold and another of
silver, each weighing exactly the same as the crown. Of
course the balls were not the same size, because silver is
lighter than gold, and so it takes more of it to make the
same weight. He first put the gold ball into a basin of
water, and marked on the side of the vessel the height to
which the water rose. Next, taking out the gold, he put in
the silver ball, which, though it weighed the same, yet, being
larger, made the water rise higher ; and this height he also
marked. Lastly, he took out the silver ball and put in the
crown. Now, if the crown had been pure gold, the water
would have risen only up to the mark of the gold ball, but
it rose higher and stood between the gold and silver mark,
showing that silver had been mixed with it, making it more
bulky. This was the first attempt to measure the specific

24

SCIENCE OF THE GREEKS.

PT. I.

gravity of different substances, that is, the weight of any-
particular substance compared to an equal bulk of water.

It wiU be quite sufficient if you remember the experiment
as I have explained it j but as you may perhaps be puzzled
to see how it can have anything to do with weight, you can,
if you wish, try to master the following explanation of Fig. i,

Fig. I.

0|~J 0

a 1 '^'^

,t 5

.: 5-F

10 -p 10

10 -t

c

; :

Brr- 15

.. 15--

Diagram showing the difference of specific gravity between equal weights of gold,

silver, and mixed metal.
ABC, Spring balances, d. Gold ball weighing 19 oz. e. Silver ball weighing 19 oz.

f. Crown of mixed metal weighing 19 oz.

which shows how specific gravity is measured. You must
begin by remembering that the crown, the gold ball, and the
silver ball, when weighed in the air, will all pull the marker of
the spring balances a, b, c, down to 1 9 ; that is, they will all
weigh 19 ounces. But when they are immersed in water they

CH. III. ARCHIMEDES— SPECIFIC GRAVITY. 25

will no longer weigh the same, because the water round
them buoys them up just as much as it would buoy up the
quantity of water which they displace.

Now, the gold ball takes the place of as much water as
would weigh one ounce if you could take it out and weigh it
in the air. So the gold ball is buoyed up one ounce by the
water round it, and accordingly you see it only pulls the
marker down 18 ounces instead of 19. But the silver ball,
although it weighs the same, is larger, and takes the place of
nearly two ounces of water, therefore it is buoyed up nearly
two ounces, and only pulls the marker down to 1 7. Now, as
the crown weighs the same as the two balls, its shape is of
no consequence ; if it was made all of gold it would take as
much room, and be buoyed up as much as the gold bail. If
it was all silver it would be buoyed up as much as the silver
ball, and therefore, as it pulls the marker down half-way
between 17 and 18 ounces, it must be half gold and half
silver.

In this way Archimedes showed how we can learn the
weight of any substance compared to an equal bulk of water,
and this is called the * specific gravity ' of the substance.

He also invented a screw for pumping up water, which is
still called the 'screw of Archimedes.'

Archimedes was unfortunately killed in the city of
Syracuse when it was besieged by the Romans during the
second Punic war. The General Maecenas had given special
orders that his life should be spared ; but he was so deeply
engaged in solving a problem that he heard nothing of the
din of war around him, and a common soldier not being
able to get any answer from him, killed him without knowing
who he was.

26 SCIENCE OF THE GREEKS. PT. i.

CHAPTER IV.

280 TO 120 B.C.

Erasistratus and Herophilus study the Human Body — Eratosthenes the
Geographer lays down the First Parallel of Latitude, and the First
Meridian of Longitude — He measures the Circumference of the
Earth — Hipparchus writes on Astronomy — Catalogues 1,080 Stars
— ^Calculates when Eclipses will take place — Discovers the Pre-
cession of the Equinoxes.

Erasistratas and HeropMlus. — At the time when Archi-
medes was studying in Alexandria, two physicians were
teaching there, who are famous in the history of anatomy^ or
the structure of the body. The one was Erasistratus and
the other Herophilus. The birthplaces and dates of these
two physicians are doubtful, but we know that they were the
first men who dissected the human body, and gave a clear
account of its parts. Erasistratus, in particular, described
the brain and its curious windings or convolutions, and the
division between the cerebrum or front part and the cere-
bellum or hinder and lower part. He seems also to have
known that it is in our brain that we feel everything, and
that it is the nerves which carry messages from different
parts of our body to our brain. Herophilus traced out the
tendons or strong cords which fasten the muscles to the
bones, the ligaments or fibrous cords which unite one bone
to another ; and the nerves. He is the first physician who
pointed out that in feeling a pulse you must notice three

CH. IV. ERATOSTHENES— PARALLEL OF LATITUDE. 27

things : ist, how strongly it throbs j 2nd, how quickly; 3rd,
whether the beats are regular or irregular. Many of the
names which Erasistratus and Herophilus gave to parts of the
body are still used by anatomists, and the school of medi-
cine founded by them in Alexandria was renowned for more
than six hundred years.

Eratosthenes, 276. — We must now turn to the science of
geography, which at this time began first really to be studied
by a Greek named Eratosthenes, born at Cyrene 276 b.c.
Like all men of science of that day, he too came to Alex-
andria, where the king, Ptolemy Evergetes, made him keeper
of the Royal Library. He made a map of all the world that
was then known, and described the countries of Europe,
Asia, and Libya. But his two great works were, laying
down the first parallel of latitude, and trying to measure the
circumference of the earth. He laid down the parallel of
latitude in the following manner. He knew that at all
places on the equator the day was exactly the same length
all the year round, and that the length of the days and
nights varied more and more as you went northwards;
therefore he reasoned that, if he could draw a line east and
west through a number of places whose longest day was
exactly the same length, those places would all be at the
same distance from the equator. He began at the Straits of
Gibraltar, where the longest day was exactly 14 J hours, and
then observing all those places whose longest day was also
14J hours, he drew a line through the south coast of Sicily,
across the south of the Peloponnesus, the island of Rhodes,
the bay of Issus, and across the Euphrates and Tigris, out
to the mountains of India. If you follow this line on a
map you will find it is the 36th parallel of north latitude,
and that Eratosthenes' observation was perfectly correct.

28 SCIENCE OF THE GREEKS. PT. I.

This discovery led him on to try and measure the cir-
cumference of the earth. Having found a line straight
round the earth from east to west, he knew that if he drew
a line at right angles to it, that is exactly north and south,
he should have a line which would describe a circle round
the earth from pole to pole, as the equator marks a circle
round the earth midway between the two poles. This
second line he drew from Alexandria, and it passed right
through Syene, now called Assouan, one of the southern
cities of Egypt, and thus he knew that Alexandria and
Syene were on the same meridian of longitude.

Now he found that at Syene the sun was exactly over-
head at midday, at the time of the summer solstice. He
knew this by means of a gnomon, or upright pillar (b, Fig. 2),
which was used by the Greeks to measure the height of the
sun in the sky. At Syene this pillar cast no shadow at noon
of the summer solstice, proving that the sun shone straight
down upon the top of it ; and this was further proved by the
sun shining down to the bottom of a deep well, which it
would not do unless it were directly overhead. But at
Alexandria the gnomon did cast a shadow, because, as
Alexandria was further north and the earth is round, the
sun there was not directly overhead. Now, as light
travels in straight lines (see p. 21), a line Urawn from
the extreme point of the shadow cast by the pillar or
gnomon up to the top of the pillar itself would, if carried
on, run straight into the sun, and thus the angle between
this line and the pillar showed at what angle the sun's rays
were falling at Alexandria. By measuring this angle, Eratos-
thenes found that Alexandria was g'-g-th of the whole circum-
ference of the earth north of Syene, where the rays were
perpendicular. You can form an idea of this from the
accompanying diagram, Fig. 2.

CH. IV. CIRCUMFERENCE OF THE EARTH.

29

Let the large circle represent the earth ; b the gnomon
at Syene, and a the gnomon at Alexandria. The length of
the shadow c d of the gnomon a, will bear the same pro-
portion to the circumference of the small circle (drawn from
the top of the gnomon as
a centre), that the distance
from Alexandria to Syene
(d to e) does to the whole
circumference of the globe.
This is true only if the rays
from the sun to Alexandria
and to Syene are parallel
(or run at equal distances).
They are not really quite
parallel because they meet
in the sun, but Eratosthenes
knew that the sun was at
such an enormous distance
that their approach to each
other was quite unimpor-
tant. He now measured the distance between Alexandria
and Syene and found it to be 5,000 stadia, or about 625
miles, and multiplying this by 50 he got 625 x 50 = 31,250
miles as the whole circumference of the earth, measured
round from pole to pole. This result is not quite correct,
but as nearly as could be expected from a first rough
attempt. Eratosthenes also studied the direction of moun-
tain-chains, the way in which clouds carry rain, the shape of
the continents, and many other geographical problems.

HipparelLUS, 160.— Nearly one hundred years after
Eratosthenes, the great astronomer Hipparchus was bom,
160 B.C. Hipparchus was the most famous of all the astro-

Diagram showing how Eratosthenes mea-
sured the circumfelfence of the earth.

A, Gnomon at Alexandria, b, Gnomon at
Syene. c d. Length ofshadow of gnomon.
D E, Distance from Alexandria to Syene.

30 SCIENCE OF THE GREEKS. pt. r.

nomers who lived before the Christian era. He collected
and examined all the discoveries made by the earlier obser-
vers, and made many new observations j but astronomy had
now become so complicated that the problems are too diffi-
cult to be explained here. Hipparchus made a catalogue of
1, 08.0 stars, and showed how they are grouped with regard to
the ecliptic. He also calculated accurately when eclipses of
the sun or the moon would take place. But his great disco-
very was that called the ' Precession of the Equinoxes.' This
is a veiy complicated movement which you can only under-
stand by reading works on Astronomy \ but I will try to give
a rough idea of it, in order that you may always connect it
with the name of Hipparchus.

We have seen that the earth has two movements — one,
turning on its own axis causing day and night ; the other,
travelling round the sun, causing the seasons of the year.
But besides these it has a third curious movement, just like
a spinning-top when it is going to fall. Look at a top a
little while before it falls, and you will see that, because it is
leaning sideways, the top of it makes a small circle in the
air. Now our earth, because it is pulled at the equator by
the sun, moon, and planets, makes just such a small circle
in space ; so that, instead of the north pole pointing quite
straight to the polar star, it makes a little circuit in the
sky, with the polar star in the centre. The pole moves
very slowly, taking twenty- one thousand years to go all
round this circle. To understand the effect of this move-
ment we must examine more closely what the equinoxes
are. Take your ball again and make it go round the lamp
with its axis incHned (see p. 20). When you have it in such
a position that the north pole is in the dark, or the northern
winter solstice, you will find that a straight line drawn from

en. IV. PRECESSION OF THE EQUINOXES. 31

the sun to the centre of the earth will not meet the equator
but a point to the south of it. But now pass the ball on to
the next point when neither pole is in shade, and when it is
equal day and equal night over the globe (our spring equi-
nox), a line now drawn from the sun will fall directly upon
the equator, so that the sun's path meets the equator at
this point, which is called the equinoctial point. Pass on
till the south pole of your ball is in the dark, the sun will
now fall directly on a point noiih of the equator (making our
summer solstice). Pass on again to the point of equal day
and equal night, and the sun again falls direct on the equa-
tor, causing our autumn equinox.^ _NoWj_if_theearth did not
make that small circlein_space_l i k e ^the top, the sun ^ould_
always touch the equator^at exactly those same points of
the eartTi's <?r7// or path round the sun; but the effect of
That movement is to pull the equator slightly back, so
that the points where the ecliptic and the equator cut
each other are 5 of seconds more to the west every year,
and in this way the equinoxes travel all round the orbit
from east to west in 21,000 years. Hipparchus discovered
this pre-cession (or going forward) of the equinoxes ; though
he did not know, what Newton afterwards discovered, that
it is caused by the sun and moon pulling at the mass of
extra matter which is gathered round the equator.

32 . SCIENCE OF THE GREEKS. ft. I.

CHAPTER V.

FROM A.D. 70 TO 200.

Ptolemy founds the Ptolemaic System — He writes on Geography —
Strabo, a great traveller, -writes on Geography — Studies Earth-
quakes and Volcanoes — Galen the greatest Physician of Antiquity —
Describes the Two Sets of Nerves — Proves that Arteries contain
Blood — Lays down a theory of Medicine — Greece and her
Colonies conquered by Rome — Decay of Science in Greece — Con-
cluding remarks on Greek Science.

Ptolemy, a.d. 70.— After Hipparchus there were many good
astronomers at Alexandria, but none whom we need notice
until the year 70 after Christ, when Ptolemy Claudius, a
native of Egypt, was born. He was not one of the Ptole-
mies who governed Alexandria, and the place of his birth is
unknown, but he is famous for having made a regular system
of astronomy founded upon all that the Greeks had learnt
about the heavens. His discoveries, like those of Hippar-
chus, are too complicated for us to discuss here ; they re-
lated chiefly to the movements of the moon and the planets;
but the one great thing to be remembered of him is,_that he
jbunded wJiaLis .xall£Ld-,t;ha JPtolemak System oi. astronomjj^
^vhich tries to explain all the movements of the sun, stars,
and planets, by supposing the earth to stand still in the
centre of them all. This^stemJs^jiiitained-iiL-Ptolemy's
great work caJlled_JJhe_Syntaxis/ may seem strange that,
as it is not true that^the_earth is_.tli£-.centre,_ Ptolemy should
have been able to explain so much by his system, but you

CH. V. PTOLEMY AND STRABO. ' 33

must ' remember that it had the same effect whether you
moved roim3riKe^r]7"or" tlie^bal^tTound "yoii iiTQur experi-
ment jm^gage.X9,X andPtole^ explanations were apparently
^o near the truth that astronomers were satisfied with them for
1,400 years, till Copernicus discovered the real movements.

Ptolemy was a geographer as well as an astronomer ;
he wrote a book on geography which was used in all the
schools of learning for nearly fourteen hundred years. He
drew maps of all the known parts of the world, and laid
down on them lines of latitude and longitude, which he cal-
culated by the rules Eratosthenes had discovered. In his
geography he describes the countries from the Canary Islands
on the west to India and China on the east, and from Norway
to the south of Egypt. He describes our island under the
name of Albion, or Britain, and traces out many of the coast-
lines and rivers. He also gives the names of the various
towns, with their latitude and longitude.

Strabo.— A little before the time of Ptolemy there lived
a famous traveller named Strabo, who wrote a great deal on
geography. He was born at Amasia, in Cappadocia, and
was probably living when Christ was born. Strabo in his
book describes the countries which he visited and read about.
He also studied earthquakes and volcanoes, and pointed out
that, when the hot vapour and lava hidden in the crust of
our earth cannot escape, they cause earthquakes, but that
when they find their way out through a volcano, like Etna,-,
the country is not so often disturbed and shaken.

Galen, 131. — There is still one more great man of science
whom we must mention as belonging to the Greek school at
Alexandria. This was Galen, one of the most celebrated
physicians of antiquity. He was born a.d. 131, at Perga-
mos, in Asia Minor, and during his life he is said to have

34 SCIENCE OF THE GREEKS. PT. i.

written more than 500 valuable essays on medicine and the
human body. You will remember that Erasistratus and
Herophilus dissected the human body j but in the time of
Galen this seems to have been forbidden, and he was obliged
to work upon monkeys and other animals. Even from these,
however, he learnt some very important facts. For instance,
he discovered the difference between the two sets of nerves
which we have in our body, called the nerves of sensation
and the nerves of motion.

Our bodies are provided with two sets of fine cords or
threads called nerves ; one set running from different parts of
the body to the spine and the brain, and the other set run-
ning back from the spine and brain to the body. If you
touch a hot iron with your finger, the nerves of sensation,
that is, of feeling, carry the message to your brain that
the iron is hot, and then instantly the nerves of motion
carry the message back from your brain to your finger, and
you snatch it away. If you were to cut the nerves of your
finger you would not feel pain nor draw your finger away.
You will remember that Erasistratus had an idea that it is in
our brain that we feel ; Galen proved this by many experi-
ments, though he did not understand clearly the whole
action of the nerves. He also proved that the veins of our
body contain blood, and he described the two muscles which
by their contraction pull down the lower jaw as we open
^nd pull it up as we shut our mouths. Besides these and
many other discoveries, Galen worked out a whole theory of
medicine, and how doctors were to treat their patients, and
his rules were the guide of physicians for many hundred
years.

Concluding Remarks on Greek Science. — V/e have now
come to an end of the science of the Greeks. You will

CH. V. CONCLUDING REMARKS. 35

read in Grecian history how Greece and the Greek colonies
were conquered by- the Romans more than a hundred years
before Christ was born; and when the Greeks ceased to be a
free people they gradually lost their love of discovery and
of science. The school at Alexandria continued to be
famous for many centuries after Christ, but the professors
who taught there only repeated the sayings of Ptolemy,
Aristotle, Galen, and the other great discoverers, and did
not find out new facts for themselves; and at last, in the year
640 after Christ, the Arabs took possession of the city, and
it soon ceased altogether to be Greek.

You must remember that in these five chapters we have
only been able to speak of some of the greatest men, and
then only of a few of the discoveries they made. You will
hear of many celebrated Greek philosophers, as, for example,
Socrates and Plato, whose names are not mentioned here be-
cause they wrote on subjects such as the mind and the soul,
which belong to higher philosophy, and not to Natural
Science. You will also hear of many strange and absurd
notions about the causes of things which in those early
days were held, even by such men as Pythagoras or Galen ;
but in this book we have only to try to understand the real
facts which have been discovered ;^and there is no doubt
that the Greeks, by a patient study of nature, and by making
real and careful observations and experiments, laid the
foundation of much of the knowledge which we have carried
so much further in modem times. The moment they began
merely to repeat the teachings of others, instead of trying
and proving the truth of them, they made no more disco-
veries, but lost a great deal they had gained. For a mere
reading of books will not teach science ; and if you admire
these men for making great discoveries, and would like to

36 SCIENCE OF THE GREEKS. pt. i.

be a discoverer yourself, you must not be content with
knowing what has been done, but must set to work as they
did, and observe and make experiments for yourself. \

Chief Works consulted. — Draper's 'Intellectual Development in
Europe ; ' Lewis's * Astronomy of the Ancients ; ' ' Encyclopaedia Bri-
tannica,' art. 'Astronomy ;' Herschel's 'Astronomy;' Baden Powell's
'History of Natural Philosophy;' Lardner's 'Cyclopaedia,' 1834;
Sprengel's ' Histoire de la Medecine,' 1815 ; Grant's ' History of
Physical Astronomy ; ' Lange's ' Geschichte des Materialismus ; ' Rees's
'Encyclopaedia;' Whewell's 'History of Inductive Sciences.'

PART IT.

SCIENCE OF THE
MIDDLE OR DARK AGES

FROM A.D. 700 TO A.D. 15QO

Chief Men of Science in the Middle Ages.

Marcus Grsecus

Geber or Djafer

Albategnuis

Ben Musa .

Avicenna .

Gerbert

Ebn Junis .

Alhazen

Roger Bacon

Vitellio

Flavio Gioja

Columbus .

Vasco de Gama

Ferdinand Magellan

Leonardo da Vinci

A.D.

800.
830.

879.

900.

980.
1000.
1008.
1000.
1214.
1220.
1300.

1435.
1450.

1470.

1452.

CH. VI. SCIENCE OF THE ARABS. 39

CHAPTER VL

SCIENCE OF THE ARABS-

Dark Ages of Europe — Taking of Alexandria by the Araos and burning
of the Library — The Arabs, checked in their conquests by Charles
Martel, settle down to Science — The Nestorians and Jews trans-
late Greek Works on Science — Universities of the Arabs — Chemistry
first studied by the Arabs — Alchemy, or the attempt to make
Gold — Hermes the first Alchemist — Hermetically-sealed Tubes —
Gases and Vapours called ' Spirits ' by the Arabs — The use of this
Word retained by us.

Arabian Science. — We have now arrived at what have been
called the ' Dark Ages/ because for several hundred years
Europe was too much engaged in wars and disputes to pay-
any attention to learning or science. You have, no doubt,
read in history how the Goths and Vandals, a barbarous
people from north-eastern Asia, spread themselves over
Europe, conquering the Romans, and taking possession of
all their colonies. They even crossed over into Africa, but
were driven out again by the famous General Belisarius, in
the reign of Justinian, Emperor of Constantinople. This
was in the year a.d. 534, and the Romans held Alexandria
again for about one hundred years, and then came the Arabs
or Saracens, pouring out of Arabia, and they took posses-
sion of Alexandria in the year a.d. 639, only seven years
after the death of their great leader Mahomet.

The first thing they did on taking the city was to burn
the famous library of Alexandria, and it seemed as if they

40 SCIEKCE OF THE MIDDLE AGES. pt. il.

were going to destroy the last remnant of the science of the
Greeks. But it proved otherwise : they went on conquering
and destroying till they had overrun all the north of Africa
up to the Straits of Gibraltar, had taken a great part of Spain
and even of the south of France as far as the river Aude, in
Languedoc, and then when Charles Martel, mayor of the
Franks, conquered them at Tours in 732, and stopped them
from going any farther, they settled down and began to give
their attention to science and learning.

They found in Arabia and in Egypt two classes of people
who were able to teach them the science of the Greeks.
These were the Nestorians and the Jews. The Nestorians,
or followers of Nestorius, Bishop of Constantinople, were a
peculiar sect of Christians, who had fled into Arabia about
the year 450, that they might found a Church of their own.
They became very powerful and learned, and translated
many of the Greek works of science into the Arabian
language. The Jews, after the fall of Jerusalem, had also
taken refuge in Syria and Mesopotamia, and they were very
skilful in medicine, and founded many medical colleges.
The Arabian schools of Bagdad, Cairo, Salerno in the south
of Italy, and Cordova in Spain, soon became famous all
over the world. The Arabs were not able to practise
anatomy in their medical schools, because the Koran, that
is the Mahommedan Bible, taught that it was not right to
dissect the human body, so they turned their attention
chiefly to medicine, trying to discover what substances they
could extract from plants and minerals, at first to serve as
medicines but soon for very different uses.

Arabian Alchemists. — They found something in the old
Greek writings about the way to melt stones or minerals, so
as to get out of them iron, mercury, and other m.etals ; and

CH. VI, ARABIAN ALCHEMISTS. 41

also how to extract many beautiful colours out of rocks and
earths. But the chief thing which interested them in the
books of the Egyptians, Chaldeans, and Greeks, was the
attempts these nations had made to turn other metals into
gold, a discovery which tradition said had been made by Her-
■ mes Trismegistus about 2,000 years before Christ. We know
very little of this Hermes, and indeed we are not sure
whether he is not altogether an imaginary person ; but the
alchemists, as the people were called who tried to make gold,
considered themselves followers of Hermes, and often called
themselves Hermetic philosophers. To melt the mouth of a
glass tube so as to close it was called securing it with ' Her-
mes, his seal,' and even to this day a bottle or jar which is
closed so that it is air-tight is said to be hermetically sealed.

The Arabs were a very superstitious people, and believed
in all kinds of charms ; and this idea of making gold in a
mysterious way took a great hold of them. Many thousands
of clever men occupied themselves in the supposed magic
art of alchemy. We need not study it here, but only observe
how very useful it was in teaching the first facts of chemistry.
These men, who were many of them learned, clever, and
patient, spent their lives in melting up different substances
and watching what changes took place in them. In this
way they learnt a great deal about the materials of which
rocks, minerals, and other substances are made.

One of the first things they discovered was that by
heating some substances, such as nitre or saltpetre, they
drove something out of them which was invisible, and yet
that they could collect this invisible something in bottles;
and in some cases, if they put a light to it, it exploded
violently, breaking the bottle to atoms. Now, because this
was invisible and yet so powerful, they thought it must be

42 SCIENCE OF THE MIDDLE AGES. pt. ii.

like the spirit of man, which can do so much and yet cannot
be seen, and for this reason they called it ' spirit/ We know
now that when we heat substances we separate part of the
matter of which they are made into very small portions,
which float off as steam or gas into the air; so that this
spirit noticed by the Arabs was vapour or gas.

It seems almost certain that the Arabs knew a great deal
about gunpowder and some other mixtures which explode
when they are set on fire. An Arab named Marcus Grsecus,
who lived about the beginning of the ninth century, says that
if you mix together one pound of sulphur, two of charcoal,
and six of saltpetre, it will explode when you light it -and
drive things into the air. This is one of the ways in which
gimpowder is still made.

CH. VII. CHEMISTRY OF GEBER. 43

CHAPTER VII.

SCIENCE OF THE ARABS (CONTINUED).

Geber, or Djafer, the founder of Chemistry — His Explanation of Dis-
tillation— Of Sublimation — Discovers that some Metals increase in
weight when heated — Discovers strong Acids — Nitric Acid —
Sulphuric Acid — Discovery of Sal-Ammoniac by the Arabs — Arabs
mix up Astronomy with Astrology — Albategnuis calculates the
Length of the Year — Mohammed Ben Musa, first writer on Algebra
— Uses the Indian Numerals — Gerbert introduces them into Europe
— Alhazen's discoveries in Optics — His Explanation why only one
image of each object reaches the Brain — His discovery of Refrac-
tion, and of its effect on the light of the Sun, Moon, and Stars — His
discovery of the magnifying power of rounded glasses.

Geber' s discoveries in Chemistry, 800-900.— The greatest
of the Arabian alchemists was a man named Geber, or
Djafer, who was born in Mesopotamia about a.d. 830.
He has been called the * Founder of Chemistry,' for though,
like his countrymen, he spent much of his time in trying to
make gold, yet he is the first who, as far as we know, made
really useful chemical experiments.

He explains in his works many of the methods we now
use in chemistry. For example, he states that if you boil
water, the vapour (or spirit as he calls it) will rise up, and
you can collect it and cool it down again in another vessel j
and it will then be pure, because any solid matter such as
sand or salt, which does not turn readily into vapour, will
remain behind in the first vessel. Again, if you heat wine or

44 SCIENCE OF THE MIDDLE AGES. pt. ii.

brandj gently, a vapour called alcohol or spirits of wine will
rise up, because the alcohol turns into vapour more easily
than the other materials of the wine. If you collect and cool
down this vapour in another bottle, you will have the liquid
spirits- of- wine. This process is called distillatioti, and is
used by chemists to separate substances which turn readily
into vapour from others which do not boil so easily. You
can distil vapours from solid things as well as from liquids :
if you heat sugar over a fire, it will soon boil, and a vapour
will rise up from it.

But if you put a piece of camphor in a flask with a
stopper to it, and heat it very gently either by placing it in
the sun or at some distance above a lighted candle, the cam-
phor will gradually disappear from the bottom of the flask,
and collect in little crystals on the inside of the neck. This
is because camphor at an ordinary heat changes straight into
a dry invisible gas, without first, becoming liquid as ice does.
The process by which substances are turned directly from
a solid state into a dry gas is called sublimation, and Gefer
describes it in his book as ' the elevation of dry things by
fire.' He knew that if you take a kind of stone called
cinnabar, and heat it, a dry gas rises from it, which you can
collect, and which cools do\\Ti into drops of mercury or
quicksilver.

Geber made another remarkable experiment, though he
did not thoroughly understand it. He states in his book
that if you take a certain weight, say a pound, of iron, lead,
or copper, and heat it in an open vessel, the metal will weigh
more after it has been heated than it did before, which
seems very strange, as we cannot see that anything has been
added to it. We shall learn the reason of this when we
come to the discoveries of Priestley (chap, xxvii.) ; but Geber

CH. VII. GEBER DISCOVERS ACIDS, 45

carefully noticed the fact, though he could not explain it.
But the discovery which most of all gives Geber the right to
be called the ' founder of chemistry ' was that of strong
acids. Most of the chemical experiments we make now
v/ould be impossible without acids, but before Geber's time
vinegar seems to have been the strongest acid known. He
found, however, that by heating copperas (or sulphate of
iron) with saltpetre and alum, he could distil off a vapour
which cooled down into a very strong acid, now called
nitric acid. He used this to dissolve silver, and by mixing
it with sal-ammoniac he found it would even dissolve gold.
Sal-amm9niac was a kind of salt which was known to the
Arabs before Geber's time. They made it by heating the
dung of camels, and the name ammoniac was given to it
because they made it first in the desert near the temple of
Jupiter Ammon. Geber also made stdphuric acid by dis-
tilling alum. When we remember that all these experiments
were made more than a thousand years ago, we must
acknowledge that Geber deserves great honour for the dis-
coveries which he made.

Albategnuis, 879. — We have seen that in chemistry the
Arabs learned very little from the Greeks, but in mathe-
matics and astronomy they found a great deal written, and
the Arabian astronqmers spent much of their time in trans-
lating Greek works. Unfortunately they mixed up astronomy,
or the study of the heavenly bodies, with astrology, a kind of
magic art, by which they imagined they could foretell what
was going to happen by studying the stars. In spite of this,
however, there were several very celebrated Arabian astro-
nomers, one of whom, called Albategnuis, born a.d. 879,
made a great many good observations. He calculated the
length of the year more exactly than Ptolemy had done,

46 SCIENCE OF THE MIDDLE AGES. PT. II.

making it 365 days, 5 hours, 46 minutes, 24 seconds, which
was only two minutes shorter than it really is, and he cor-
rected many more of Ptolemy's observations. After him
the next famous Arabian astronomer was Ebn Junis,
A.D. 1008, who drew up several valuable astronomical
tables.

Ben Musa, 900. — Of mathematicians, one of the most
celebrated was Mohammed Ben Musa, who lived about
A.D. 900. He is the earliest Arabian writer on algebra,
or the working of sums by means of letters. This name
* Algebra ' is an Arabian word, and the Arabs were very
clever at this way of making calculations. Ben ^ Musa is
the first writer we know of who used the Indian numerals
I, 2, 3, 4, 5, 6, 7, 8, 9, o, instead of the clumsy Roman nu-
merals I, II, III, IV, &c. If you try to do a sum with the
Roman numerals you will see what a troublesome business
it is and what a great gain the Indian numerals are. The
Arabs learned these numbers from the Hindoos, and always
used them after the time of Ben Musa, so that they are now
generally called the Arabic numerals. About the year 1000.
a Frenchman named Gerbert, Archbishop of Rheims, and
afterwards Pope Sylvester the Second, who had been edu-
cated at the famous Arabian University of Cordova in
Spain, introduced them into Europe. The word cipher.
which we use for o, comes from an Arabic word, ctphra.
meaning empty or void.

Alhazen's discoveries in Optics, 1000. — Another Arabian
whom we must specially mention was an astronomer and
mathematician named Alhazen, who was born at Bassora, in
Asiatic Turkey, about the year a.d. iooo, but who spent
most of his life in Spain. He made discoveries chiefly in
optics, or the science of sight. He was the first to teach that

CH. VII. ALHAZEN ON REFRACTION. 47

we see things because rays of light from the objects around
us strike upon the retina or thin membrane of our eye, and
the impression is carried to our brain by a nerve. When
the object is itseh' a light, like the flame of a candle, it gives
out the rays which reach our eye ; but when, like a book or a
chair, it is not luminous, then the rays of the sun or any
other light-giving body are reflected from it to our eye and
make a picture there. Alhazen also explained why we do
not see two pictures of one object although we look at it
with two eyes ; he pointed out that, as the reflection of any
given point of the object is formed on the same part of the
one eye as of the other, only one united picture reaches the
brain. This is the best explanation which has ever been
given of why we only see one image, but even to this day we
are not quite certain that it is satisfactory.

Alhazen discovered another wonderful thing about light.
If you take a straight stick and hold
it in a slanting direction in a basin
of water so that half of it is under '^'\X
water, the stick will appear to bend N.

at the point a, where it touches ^^^

the surface of the water, and in- \i^^^^^0^

stead of going along the dotted ^^^^^^^

line to B, will look as if it went

to the point c. This is because rays of light are bent in a
slanting or oblique direction when they pass through sub-
stances of different density. Water is more dense than air,
and therefore the rays of light reflected from the stick are
bent as they pass out of the water into the air on their way
to your eye. This is called refraction^ or the breaking-back
of a ray, and the discovery of it led Alhazen to find the
explanation of a very curious natural fact.

48

SCIENCE OF THE MIDDLE AGES.

PT. II.

He knew that the air round our globe grows denser as it
gets nearer the earth, so he argued that the slanting rays
from the sun, moon, and stars must become bent as they
approach the earth and pass through the denser air. This,
he said, causes us to see the sun after it has really sunk
below our horizon at night, and before it rises in the
morning ; for the rays are gradually curved by passing
through the denser air round our earth. Fig. 4 explains this.

Fig. 4.

Eartn

Bending of the Sun's rays by the atmosphere.

s. Sun. s c and s v>, Rays as they would travel if there were no atmosphere.
' s B A, Ray bent so that the sun becomes visible at A.

Supposing the sun to be at s, and a person at a, it is clear
that any straight ray from the sun, such as s d, could not
reach A, because part of the earth is in the way; neither
could a ray, s c, reach the earth, because it would pass
above it. But when the rays from s to C strike the at-
mosphere at B, they are bent out of their course, and are
gradually curved more and more by the denser air till they
are brought down to the earth at a, and so the sun becomes
visible.

Alhazen was also the first to remark that a convex lens,
that is, a glass with rounded surfaces, such as our common
magnifying glasses and burning glasses, will make things
appear larger if held at a proper distance between the eve

CH. VII.

ALHAZEN— MAGNIFYING GLASSES.

49

and any object, because the two surfaces of the glass, be-
coming more and more oblique to each other as they
approach the sides, bend the rays inwards, so that they come

Fig. 5.

A

B

Arrow magnified by a convex lens.

to a focus in the eye. To understand this, draw a line of
any kind, say a little arrow, on a sheet of paper, and bring
your eye near to it. Your arrow being so close would
look very large if you could see it distinctly, but just be-
cause it is so near, your eye cannot focus or collect together
the rays coming from it so as to make a picture on the
retina at the back of the eye ; therefore you see nothing
but an indistinct blur. But now take a magnifying glass,
c D, fig. 5, and hold it between your eye and the arrow. If
you hold it at the right distance you will now see the arrow
distinctly, because the greater part of the rays have been
bent or refi-acted by the rounded glass so as to come into
focus on your retina. But now comes another curious fact.
It is a law of sight, that when rays of light enter our eye we
follow them out in straight lines, however much they may
have been bent in coming to the eye. So your arrow will
not appear to you as if it were at a b, but, following out the
dotted lines, you will see a magnified arrow, A b, at the

I

50 SCIENCE OF THE MIDDLE AGES. pt. ii.

distance at which you usually see small objects distinctly.
This observation of Alhazen's about the bending inwards or
converging of rays through rounded glasses was the first step
towards spectacles.

Besides the Arabians whom I have mentioned here,
there were many who were very celebrated, but we know
very little of their works. Among them was Avicenna
A.D. 980, whom you will often hear mentioned as a writer on
minerals. But the chief thing to be remembered, besides
the discoveries of Geber and Altiazen, and the introduction
of the Indian numerals, is that in the Dark Ages, when all
Europe seemed to care only for wars and idle disputes, it
was the Arabs who kept the lamp of knowledge alight and
patiently led the way to modern discoveries.

CH. VIII. ROGER BACON. 51

CHAPTER VIII.

SCIENCE OF THE MIDDLE AGES (CONTINUED).

Roger Bacon — His ' Opus Majus ' — His Explanation of the Rainbow —
He makes Gunpowder — Studies Gases — Proves a Candle will not
burn without Air — His Description of a Telescope — Speaks of
Ships going without Sails— Flavio Gioja invents the Mariner's
Compass — Greeks knew of the Power of the Loadstone to attract
Iron — Use of the Compass in discovering new lands — Invention
of Printing — Columbus discovers America — Vasco de Gama sees
the Stars of the Southern Hemisphere — Magellan's ship sails
round the World — Inventions of Leonai'do da Vinci,

We must now return to Europe, where the nations were
struggling out of the Dark Ages; and though there were
many learned men in the monasteries, very few of them paid
any attention to science : while those who did, often lost their
time in alchemy, trying to make gold j or in astrology, pre-
tending to foretell events by the stars.

Roger Bacon, 1214. — In the year 12 14, however, a man
was born in England whom every Englishman ought to
admire and revere, because in those benighted times he gave
up his whole life to the study of the works of nature, and
suffered imprisonment in the cause of science. This was
Roger Bacon, a great alchemist, who was born at Ilchester
in Somersetshire, educated at Oxford and Paris, and then
became a friar of the order of St. Francis. For this reason
he is often called Friar Bacon. Bacon's great work, called
the ' Opus Majus,' is written in such strange language that it

52 SCIENCE OF THE MIDDLE AGES. pt. ir.

is oftQji difficult to find out how much he really knew and
how much he only guessed at. We know, however, that he
made many good astronomical observations, and that he
explained the rainbow by saying that the sun's rays are
refiracted or bent back by the falling drops of rain, as
was also noticed about the same time by Vitellio, a Polish
philosopher.

Bacon is famous as the first man in Europe who made
gimpowder ; we do not know whether he learnt the method
from the Arabs, but it is most likely, for he gives the same
receipt for making it as Marcus Gr^ecus did — namely, salt-
petre, charcoal, and sulphur. He also knew that there are
different kinds of gas, or air as he calls it, and he tells us
that one of these puts out a flame. He invented the
favourite schoolboy's experiment of burning a candle under
a bell-glass to prove that when the air is exhausted the
candle goes out.

Bacon seems also to have known the theory of a tele-
scope. We do not know whether he ever made one, but he
certainly understood how valuable it would be. This is
what he says about it in his ' Opus Majus,' or ' Great Work ' :
* We can place transparent bodies (that is, glasses) in such a
form and position between our eyes and other objects that
the rays shall be refracted and bent towards any place we
please, so that we shall see the object near at hand, or at a
distance, under any angle we please ; and thus from an in-
credible distance we may read the smallest letter, and may
number the smallest particles of sand, by reason of the great-
ness of the angle under which they appear.' This is at least
a very fair description of a telescope. In the same book he
says that one day ships will go on the water without sails,
and carriages run on the roads without horses, and that

CH. VIII. I^LAVIO GIOJA—MARINER'S COMPASS. ^^

people will make machines to fly in the air. This shows
that he must have imagined many things which were not
really discovered till more than 300 years afterwards ; but
they were all dreams which he could not carry out himself.
Before we leave Roger Bacon I must warn you not to con-
fuse him with Francis Bacon, Chancellor of England, who
was quite a different man, and lived more than 200 years
later.

Flavio Gioja discovers the Mariner's Compass, 1300. —
About ten years after the death of Bacon, a man was born in
a little village called Amalfi, near Naples, who made a dis-
covery of great value. The man's name was Flavio Gioja,
and the discovery was that of the viai'iner's compass. Long
before Flavio's time people knew that there was a kind of
stone to be found in the earth which attracted iron. There
is an old story that this stone was first discovered by a
shepherd, who, while resting, laid down his iron shepherd's
crook by his side on a hill, and when he tried to lift it again
it stuck to the rock. Although this story is probably only a
legend, yet it is certain that the Greeks and most of the
ancient nations knew that the loadstone attracted iron ; and
a piece of loadstone is called a magnet^ from the Greek word
magnes, because it was supposed to have been first found at
Magnesia,.m Ionia.

A piece of iron rubbed on a loadstone becomes itself a
magnet, and will attract other pieces of iron. But Flavio
Gioja discovered a new peculiarity in a piece of magnetised
iron, which led to his making the mariner's compass. He
found that if a needle or piece of iron which has been
magnetised is hung by its middle from a piece of light
string, it will always turn so that one end points to the
north and the other to the south. He therefore took a

54 SCIENCE OF THE MIDDLE AGES. pt. ir.

piece of round card, and marking it with north, south, east,

and west, he fastened a magnetised needle upon it pointing

Fig. 6. from N. to s. j he then fastened

^^^^^^^^^^r~~--t the card on a piece of cork

;:^^^^B%— E— ^^^g\ ^^^ floated it in a basin of

^^^^^^T^iiL^^]] water. Whichever w^ay he

^^^^^^^^^^ turned the card round till the

^^^^^ N. of the needle pointed to

Flavio's Compass floating on water. ^^^ ^^^^^^ ^^^ ^^^ ^^ ^^ ^^^

south, and from the other marks on the card he could then
tell the direction of the west, north-west, &c.

You will see at once how important this discovery was ;
for when a ship is at sea, far from land, there is nothing to
guide the captain except the stars, and they cannot always
be seen, so that before he had a compass he was obliged to
•keep in sight of land in order to find his way. But as soon
as he had an instrument which pointed out to him which
way his ship was going, he could steer boldly and safely
right across the sea.

There has been much dispute as to who first discovered
the compass, and some people think that the Chinese used it
in very early times ; but learned men now agree that Gioja
discovered it independently, and it is certain that he was the
first to use it in a ship. Of course it would have been very
inconvenient to have it always floating in a basin of water ;
so the card was fitted, by means of a little cap, on to the top
of a pin, round which it could turn easily, and this is the way
it is still made. As the king of Naples belonged at that
time to the royal family of France, Gioja marked the north
point of the needle with a fleur-de-lys in his honour, and the
mariner's compass of all nations still bears this mark. The

CH. VIII. INVENTION OF PRINTING. 55

territory of Principiato, where Gioja was born, has also a
compass for its arms, in memory of his discovery.

Invention of Printing, 1438. — Before we go on to speak
of the wonderful voyages which followed the invention of the
compass, we must pause a moment to notice another great
change which took place about a hundred years after the
time of Bacon and Gioja. This was the invention of
printing, in the year 1438. In the early part of the fifteenth
century some people began to engrave, that is, to cut on
wood, pictures and texts of Scripture, and then to rub them
over with ink, and take an impression of them on paper.
One day it occurred to a man named John Gutenberg, of
Strasburg, that if the letters of a text could be made each
one separate, they might be used over and over again. He
began to try to make such letters, and with the help of John .
Faust of Mayence, and Peter Schoeffer of Gernsheim, both
of them working mechanics like himself, he succeeded in
making metal letters, or types as they are called. These
men finished printing the first Bible in the year 1455. In
1465 the first printing-press was started in Italy, and another
in Paris in 1469, while Caxton introduced printing into
England in 1474.

It is easy to see what a great step this invention was
towards new knowledge. So long as people were obliged to
write out copies of every work, new books could only spread
very slowly, and old books were very dear and rare \ but as
soon as hundreds of copies could be printed off and sold in
one year, the works of the Greeks on science were collected
and published by clever men, and were much more read
than before ; and what was still more important, books
about new discoveries passed quickly from one country to
another, and those who were studying new truths were able

56 SCIENCE OF THE MIDDLE AGES. pt. ii.

to learn what other scientific men were also doing. Thus
printing was one of the first steps out of the ignorance of the
Dark Ages.

Voyages round the World. — The next step, as I said
just now, was made by the use of the mariner's compass.
The Greeks, as you will remember, knew that the earth was
a globe, but all this had been forgotten in Europe since the
Goths and Vandals came in, and people actually went back
to the old idea that the world was flat like a dinner-plate,
with the heavens in an arch overhead. Nevertheless, the
sailors, who saw ships dip down and disappear gradually
as they sailed over the sea, could not help suspecting that it
must be a round globe after all ; and Christopher Columbus,
a native of Genoa, was convinced he could find a way round
to the East Indies by sailing to the west across the Atlantic.
Full of this idea, he started on August 3, 1492, with three
small ships and ninety men, from Palos, near Cadiz, in
Spain, and sailed first to the Canary Islands. From there he
sailed on for three weeks, guided by his compass, but with-
out seeing any land; the food in the ship began to run
short, and his men became frightened and threatened to
throw him overboard if he would not turn back; but he
begged them to continue for three days longer, and a little
before midnight on October 1 1 there was a cry of ' land !
land ! ' and next morning at sunrise they disembarked on one
of the Bahama Islands in the New World.

Columbus thought that he had sailed right round and
reached the other side of Asia, but if you look at your map
you will see he only went a quarter of that distance. He died
in 1506, without finding out his mistake, though he made
several other voyages. During these he made a very remark-
able discovery about the magnetic needle of the compass. It

CH. VIII. VOYAGES ROUND THE WORLD. 57

had long been known that the needle did not point due
north, but a little to the east of the north. Columbus, how-
ever, found that, as he went westward, the needle gradually
lost its eastward direction, and pointed due north, and then
gradually went a little way to the west. It remained like
this till, on his return, he came back to the same place where
it had changed, and then it passed gradually back to its first
position. From this he learnt that, although the magnetic
needle always points towards the north, it varies a little in
different parts of the world. The reason of this is not even
now clearly understood, and we must content ourselves here
with knowing that it is so. %

The next grand voyage of discovery was made by Vasco
de Gama, a Portuguese, who set sail July 9, 1497, to try
whether it was possible to sail round the south of Africa.
He succeeded, and during the voyage he could not help
remarking the new constellations or groups of stars, never
seen in Portugal, which appeared in the heavens. This
proved to him that the earth must certainly be a globe, for if
you were to sail for ever round a flat surface, you would
always have the same stars above your head.

At last there came a third discoverer, Ferdinand Magellan
(or Magalhaens), of Spain, who set off August 10, 15 19, deter-
mined to sail right round the world. He steered westward
to South America, and discovered the Straits which separate
Terra del Fuego from the mainland, and which were called
after him the Straits of Magellan. Then he sailed north-
wards, across the equator again, till he came to the Ladrone
Islands, where he was killed fighting a battle to help the
native king. Sebastian del Cano, his lieutenant, then took
the command of the ship, which arrived safely back in the
port of St. Lucar, near Seville in Spain, on September 7,

58 SCIENCE OF THE MIDDLE AGES. pt. il

1522. This ship, guided by Magellan, was the first which
ever sailed quite round the world j and all these voyages,
proving that the earth is a round globe, and bringing back
accounts of new stars in the heavens, set men thinking that
there was much still to be learnt about the universe.

Leonardo da Vinci, 1452. — We must not pass on into
the sixteenth century without mentioning Leonardo da
Vinci, the great painter, who was also very remarkable for
the number of interesting inventions which he made in
mechanics. Leonardo was bom in 1452 at Vinci, in
Tuscany ; he is so generally spoken of as a painter that
many^ people do not know that he left behind him fourteen
valuable works on Natural Philosophy. He invented water-
mills and water-engines, as well as locks to shut off the
water, such as are now used on our canals and rivers. He
studied the flight of birds, and tried to make a machine for
flying, and, besides being one of the best engineers of his
day, he made many curious machines, such as a spinning-
machine, a water-pump, and a planing-machine. Some of
these things were only models which he made for his own
pleasure, but they show that he, like Roger Bacon, was very
much in advance of his age ; and he did good service to
science by the careful experiments which he made, and by
insisting that it was only by going to Nature herself that men
can really advance in knowledge.

Chief Works consulted. — Draper's 'Hist, of Intellectual Develop-
ment;' Baden Powell's ' Hist, of Natural Philosophy,' 1834; Sprengel
* Histoire de la Medecine,' 1850 ; ' Penny Cyclopaedia,' art. 'Arabians ;'
'Encyclopaedias Metropolitana and Britannica;' Rodwell's 'Birth of
Chemistry,' 1874; 'The Works of Geber,' Englished by R. Russell,

CH. yiii. SCIENCE OF THE MIDDLE AGES. 59

1678; Whewell's 'History of the Inductive Sciences;' Priestley's
'History of Vision,' 1772 ; Smith's 'Optics,' 1778; ' Edinburgh En-
cyclopaedia,' art. Chemistry J Bacon's 'Opus Majus,' by Dr. Jebb,
1733; Bacon, * Sa Vie, ses Ouvrages, et ses Doctrines,' by M.
Charles, 1861 ; Ventura, ' Ouvrages Physico-mathematiques de Leon-
ardo da Vinci,' 1797; Draper's 'Conflict between Religion and
Science,' 1875.

PART III.

RISE AND PROGRESS OF
MODERN SCIENCE

FROM A.D. 1500 TO THE PRESENT DAY

Chief Scientific Men of the Sixteenth Century

A.D.

Copernicus .... 1473- 1543.

Paracelsus .

• 1493-1541.

Vesalius .

. 1514-1564.

Fallopius .

. 1520-1563.

Eustacliius .

1570.

Gesner

. 1516-1565.

Caesalpinus

15 19-1603.

Baptiste Porta

. 1545-1615.

Gilbert

. 1540-1603.

Tycho Brahe

. 1546-1601.

Galileo

. 1 5 64- 1 642.

Stevinus .

1633.

Van Helmont

1 5 77-1 644.

Giordano Bruno

<

1600.

CH. IX. SIXTEENTH CENTURY. 63

CHAPTER IX.

SCIENCE OF THE SIXTEENTH CENTURY.

Rise of Modem Science — Dogmatism of the Middle Ages — Reasons
for studying Discoveries in the order of their dates — Copernican
theory of the Universe — Copernicus goes back to the System of
Aristarchus — Is afraid to publish his Work till quite the end of his
life — Work of Vesalius on Anatomy — He shows that Galen made
many mistakes in describing Man's Structure — His Banishment
and Death — The value of his Work to Scipnce— Fallopius and
Eustachius Anatomists — Gesner's Works on Animals and Plants —
He forms a Zoological Cabinet and makes a Botanical Garden —
His Natural History of Animals — His classification of Plants ac-
cording to their Seeds — His work on Mineralogy — Csesalpinus makes
the First System of Plants on Gesner's plan — Explains Dioecious
Plants — Chemistry of Paracelsus and Van Helmont,

We have now arrived at the beginning of Modem Science,
when the foundations were laid of that knowledge which we
possess to-day. With the exception of some original disco-
veries made by the Arabs, learned men during the Dark
Ages had spent their time almost entirely in translating and
repeating what the Greeks had taught ; till at last they had
come to believe that Ptolemy, Galen, and Aristotle had
settled most of the scientific questions, and that no one had
any right to doubt their decisions. But as Europe became
more civilised, and people had time to devote their lives to
quiet occupations, first one observer and then another began
to see that many grand truths were still undiscovered, and

64 SIXTEENTH CENTURY. pt. hi.

that, though the Greeks had learned much about nature, yet
their greatest men had only made the best theories they
could from the facts they knew, and had never intended that
their teaching should be considered as complete or final.

And so little by little real observations and experiments
began to take the place of mere book-learning, and as soon
as this happened science began to advance rapidly — so
rapidly that from this time forward we can only pick out the
most remarkable among hundreds of men who have added
to the general stock of knowledge. A detailed account of all
the steps by which the different sciences progressed would
fill many large volumes, and would only confuse you, unless
you aheady knew a great deal about the subject. In this
book we can only throw a rapid glance over the last four cen-
turies of modem science, and try to understand • such new
discoveries as ought to be familiar to every educated person.
But you cannot bear in mind too often that when we come
to a great man who discovers or lays down new laws, there
have always been a number of less-known observers who
have collected the facts and ideas from which he has formed
his conclusions, although to mention all these men would
only fill your mind with a string of useless names.

I must also explain here why I have adopted the plan
of giving new discoveries in the order in which they oc-
curred. You would no doubt have understood each separate
science better if the account of it had been carried on
without any break — if, for example, Astronomy had been
spoken of first, then Optics, then Mechanics, and so on.
But by this arrangement you would not see the gradual way
in which our knowledge has grown from century to century,
nor how the work done in one science has often helped to
bring out new truths in another. Therefore, although by

CH. IX. COPERNICAN THEORY OF THE UNIVERSE. 65

following the order of dates we shall be forced sometimes to
pass abruptly from one subject to another, it will, I think, be
the best way to teach you the ' History ' of Modern Science.
Copernican Theory of the Universe, 1474-1543. — It was
stated (p. 32) that about the year a.d. 100 Ptolemy formed a
' System of the Universe ' which supposed our little earth to
be the centre of all the heavenly bodies ; and the sun, toge-
ther with all the stars and planets, to move round us for our
use and enjoyment. This system had been held and taught
in all the schools for nearly fourteen hundred years, when,
in the beginning of the sixteenth century, a man arose who
set it aside, and proposed a better explanation of the move-
ments which we see in the heavens.

In 1473, ^ f^w years before Columbus sailed for America,
•Nicolas Copernicus, the son of a small country surgeon, was
born at Thorn, in Poland. From his earliest boyhood he
had always a great love for science, and after taking a doc-
tor's degree at Cracow, he went as Professor of Mathematics
to Rome. About the year 1500 he returned to his owm
country and was made a canon of Frauenberg, in Prussia.
Here he set himself to study the heavens from the window
of his garret, and often all night long from the steeple of
the cathedral. At the same time he read carefully the ex-
planations which Ptolemy and other astronomers had given
of the movements of the sun and planets. But none of
their theories satisfied him, for he could not make them
agree with what he himself observed j until at last, after
twenty years of labour, he came to the conclusion that
the real explanation was the one which Aristarchus had
given (p. 20), and which was called the Pythagorean System,
namely, that the sun stands still in the centre of our sys-
tem, and that the earth and other planets revolve round it.

66 SIXTEENTH CENTURY. pt. iii.

He now made a large quadrant, that is, an instrument
for measuring the angular height of the sun and stars,
and with this he made an immense number of obser-
vations on the different positions of the sun during the
year, all proving how naturally the movements of the dif-
ferent planets are explained by supposing the sun to stand
still in the middle. This he wrote down in his great
work called 'The Revolutions of the Heavenly Bodies,'
in which he taught that the earth must be round, and
must make a journey every year round the sun. He gave
his reasons why Ptolemy was mistaken in believing the
earth to be the centre of the universe, and added a dia-
gram of the orbits of our earth and of the planets round
the sun. He then went on to found upon this a whole
system of Astronomy, too complicated for us to follow
here ; but he did not publish it, because he was afraid of
public opinion j for people did not like to believe that our
world is not the centre of the whole universe. At last his
friends persuaded him to let his book be printed, and a
perfect copy reached him only a few days before his death,
which occurred in 1543, when he was seventy years of age.

This work was the foundation of modern astronomy, and
the theory that the earth and the planets move round the
sun has ever since been called the Copef^m'can TJuory ; but
at the time it was published very few persons believed in it,
and it was not till more than sixty years after the death
of Copernicus that Galileo's discoveries brought it into
general notice.

Work of Vesalius on Anatomy, 1542. — While Coper-
nicus was proving to himself that Ptolemy's theory of the
heavens was not a true one, a Belgian, named Vesalius, was
beginning to suspect that Galen, though a good physician,

CH, IX. VES ALIUS AND GALEN. 67

had described the structure of man's body very imperfectly,
because he had only been allowed to dissect animals.

Andreas Vesalius was born at Brussels in 15 14. When
he was quite a boy he had a passionate love for anatomy,
and, as he had some little fortune, he gave up all his time to
this study, and often ran great risks in order to get bodies to
dissect ; for in those days it was still considered wicked to
cut up dead bodies. In the year 1540 he became Professor
of Anatomy at the University of Padua, in Northern Italy,
and two years afterwards, when he was only twenty- eight
years of age, he published his ' Great Anatomy,' in which
Human Anatomy., or the structure of man's body, was care-
fully studied and described ; the different parts being illus-
trated by the most beautiful and accurate wood engravings,
drawn by the best Italian artists.

In this book Vesalius pointed out that Galen, having
learnt his anatomy from the bodies of animals, had described
incorrectly almost all the bones which are peculiar to man.
For example, in animals the middle part of the upper jaw,
which holds the front and eye-teeth, is a separate bone from
the sides of the jaw, and even in monkeys it remains sepa-
rate while they are young ; but man is bom with the upper
jaw all joined into one solid piece. Now Galen had de-
scribed man's upper jaw as composed of separate bones, and
therefore it was clear that he had made his description from
the skull of an animal. In all instances like this, and there
are many, in which man differs from animals, Vesalius
showed that it was necessary to examine the human skele-
ton, and not to trust merely to Galen's teaching.

This was a great step in science, and yet people had
become so accustomed to follow authority blindly that
Vesalius made many enemies by venturing to think that

6S SIXTEENTH CENTURY. pt. hi.

Galen could be wrong. It happened, unfortunately, 'that
one day when he was dissecting the body of a Spanish
gentleman who had just died, the bystanders thought that
they saw the heart throb. His enemies seized upon this
circumstance and accused him of dissecting a living man,
and the judges of the Inquisition would have condemned
him to death, if Charles V. of Spain, whose physician he
had become, had not persuaded them instead to send him
on a pilgrimage to Jerusalem. On his return from this pil-
grimage he was shipwrecked on the island of Zante, in the
Grecian Archipelago, and died of hunger when he was only
fifty years of age. There are of course many faulty descrip-
tions in Vesalius's work, for the study of anatomy was at
that time only beginning ; but he made the first attempt to
appeal io facts instead of merely repeating what others had
taught, and by this he earned the right to be called the
Founder of Modern Anatomy.

There lived at the same time as Vesalius two other very
celebrated anatomists, Gabriel Fallopius, of Modena, and
Barthelemy Eustachius, of San Severino, near Naples, who
both did a great deal to advance anatomy. Eustachius
described the tube running between the mouth and the ear
which is still called the Eitstachimi tube, and made many
very useful experiments ; but, on the other hand, he at-
tacked Vesalius very bitterly for his criticisms of Galen's
anatomy.

Gesner's Works on Animals and Plants, 1551-1565.
— We now come to one of the most interesting lives
of the sixteenth century. Many of us know very little of
astronomy or anatomy, but any child who has gathered
flowers in the country or looked at wild animals in the
Zoolorical Gardens must feel interested in Gesner, the first

CH. IX. THE FIRST ZOOLOGICAL CABINET. 69

man since the time of Aristotle who wrote anything ori-
ginal about animals and plants.

Conrad Gesner was born at Zurich in 15 16. He was
the son of very poor parents, and, being left an orphan,
was educated chiefly by the charity of an uncle and other
friends ; but his love of knowledge was so great that he
conquered all difficulties, and after taking his degree as a
medical man in 1540, earned enough by his profession,
and as Professor of Natural History at Zurich, to carry
on his favourite studies. He learnt Greek, Latin, French,
Italian, English, and even some of the Eastern languages,
and read works of science in all these tongues ; and, although
he was very delicate, he travelled all over the Alps, Swit-
zerland, Northern Italy, and France, in search of plants,
and made journeys to the Adriatic and the Rhine in order
to study marine and fresh-water fish. He employed a man
exclusively to draw figures of animals and plants, and he
made a zoological cabinet, which contained the dried parts
of animals arranged in their proper order. This was pro-
bably the first zoological cabinet which ever existed. He
also founded a botanical garden at Zurich, and paid the
expenses of it himself. He took great interest in study-
ing the medical uses of plants, and often hurt his health
by trying the effects of different herbs. His friends once
thought that he had killed himself by taking a dose of a
poisonous plant called ' Doronicum,' or ' Leopard's Bane,'
but he recovered and gave them a most interesting account
of his own symptoms.

Between the years 155 1 and 1565, Gesner published his
famous ' History of Animals,' in five parts ; two on quadru-
peds, one on birds, one on fish, and one on serpents. In this
book he describes every animal then known, and gives the

70 SIXTEENTH CENTURY. pt. hi.

countries it inhabits and the names it has been called, both
in ancient and modem languages. He calculates the ave-
rage length of its life j its growth, the number of young ones
it will bring up, and the illnesses to which it is subject; its
instincts, its habits, and its use ; and to all this he adds care-
ful drawings of the animal and its structure. Part of his in-
formation he gathered from books and friends, but a great
part he collected himself with great care, and to him we
owe the first beginning of the Natural History of Animals
in modern times.

In Botany he made the first attempt at a true classifica-
tion of plants, and pointed out that the right way to disco-
ver which plants most resemble each other is to study their
fiowers and seeds. Before his time plants had been arranged
merely according to their general appearance ; but he showed
that this system is very false, and that, however different
plants may look, yet, if their seeds or flowers are formed
alike, they should be classed in the same group. He did
not live to publish his great work on plants, but left draw-
ings of 1,500 species, which were brought out after his death.

Gesner also wrote a book on Mineralogy, in which he
traced out the forms of the crystals of different minerals and
drew many figures of fossil shells found in the crust of the
earth. The same year that this book was pubHshed he died
of the plague. When he knew that his death was certain, he
begged to be carried into his museum, which he had loved
so well, and died there in the arms of his wife.

There is something very grand and loveable in the life
of Gesner. Bom a poor boy, he struggled manfully upwards
to knowledge, and became rich only to work for science.
Everyone loved him, and he was well known as a peace-
maker among his literary and scientific friends, and for the

CH. IX. THE FIRST CLASSIFICATION OF PLANTS. 71

readiness with which he would lay aside his own work to
help others. Yet, though he had to earn his own living and
died before he was forty-nine, he became the first botanist
and zoologist of his time, and left remarkably large and
valuable works behind him. He was one of the bright
examples of what may be done by a true desire for know-
ledge, and a humble, honest, loving nature j for while he
helped others, he could never have done what he did in
zoology and botany if he had not made friends all over the
world, who were ready to send him information whenever
and wherever they were able.

First Classification of Plants by Csesalpinus, 1583. —
Nearly thirty years after Gesner's death, Dr. Andrew Csesal-
pinus, a physician and Professor of Botany at Padua, first
tried to carry out his system of grouping plants according to
their seeds. He began by dividing plants into trees and
herbs, as Theophrastus had done (see p. 17). Then he di-
vided the trees into two classes — ist, those which have the
germ at the end of the seed farthest from the stalk, as in the
walnut, where you will, find a little thing shaped like a tiny
heart lying just at the pointed end ; 2nd, those which have
the germ at the end of the seed which is nearest the stalk, as
in the apple. The herbs he divided into thirteen classes, ac-
cording to the number of their seeds and the way in which
they are arranged in the seed-vessels. Some plants, for
example, have a single pod or seed-vessel, with a number of
seeds inside it, as our common pea j others, like the poppy,
have a seed-vessel divided into a number of little cells, each
filled with seeds.

By grouping together all the plants which had the same
kind of seed-vessel, Csesalpinus made thirteen classes, and
formed a system of plants which would have been a great

72 SIXTEENTH CENTURY pt. hi.

help to botanists, and would soon have led them to make
better systems if they had followed it j but it was not gene-
rally adopted, and for nearly a hundred years longer many
went on in the old way, collecting and naming plants with-
out trying to classify them. Caesalpmus knew about 1,500
species of plants, 700 of which he had collected himself. He
was the first to point out that the use of flowers which have
no seed-vessels but only stajnens (or little thread-like stalks,
tipped with yellow powder), is to drop the powder or pollen
on flowers which have only seed-vessels and no stamens,
and by this means to cause the seeds to grow and ripen.
Such plants which have the stamens in one flower and the
seed-vessel in another are now called Dioecious plants.

Chemistry of Paracelsus and Van Helmont, 1520-
1600. — There is very little worthy of notice in the chemistry
of the sixteenth century; but we must mention in passing
two famous men : Paracelsus, who was bom 1493 at Einsiedel
in Switzerland, and Van Helmont, bom at Brussels in 1577.

Paracelsus was at one time Professor of Physic and Sur-
gery at Basle, but he gave up his professorship and travelled
about Europe during the greater part of his life. Among
other things, he pointed out that air feeds flame, and that, if
you put iron into sulphuric acid and water, a peculiar kind of
air rises from it. He also succeeded in separating gold out
of a mixture of gold and silver by using aquafortis or nitric
acid, which dissolves the silver and lets the gold fall to the
bottom of the vessel. He did not, however, make many
discoveries which are valuable now, and he taught a great
deal that was absurd and bombastic.

Van Helmont was also a wandering physician, but as a
chemist he was more careful in his experiments than Paracel-
sus. He seems to have known a great many different gases,

CH. IX. PARACELSUS AND VAN HELMONT. 73

though he did not describe them clearly, and he particularly
mentions the gas which rises from beer and other liquids
which ferment. He called this Gas sylvestre. The chief
thing to remember about Van Helmont is that he was the
first writer to use the word ' gas/ which he took from the
German word 'geist/ meaning 'spirit'

Chief Works consulted, — Rees's 'Encyclopaedia,' art. 'Coperni-
cus ; ' * Encyclopaedia Metropolitana, ' art. ' Astronomy ; ' ' Biographie
Universelle,' art. 'Copernicus;' Gassendi's 'Life of Copernicus ; '
'Encyclopaedia,'" art. 'Anatomy;' Cuvier, 'Histoire des Sciences
Naturelles,' 1845; D'Orbigny, 'Diet, des Sciences Naturelles' — In-
troduction ; ' Encyclopaedia, ' art. ' Botany ; ' Hoefer, ' Histoire de la
Physique et de la Chimie,' 1850.

74 SIXTEENTH CENTURY, pt. hi.

CHAPTER X.

SCIENCE OF THE SIXTEENTH CENTURY (CONTINUED).

Baptiste Porta discovers the Camera Obscura — Shows that our Eye is
like a Camera Obscura — Makes a kind of Magic Lantern by Sun-
light — Kircher afterwards makes a Magic Lantern by Lamplight
— Dr. Gilbert's discoveries in Electricity — Tycho Brahe, the Danish
Astronomer — Builds an Observatory on the Island of Huen — Makes
a great number of Observations, and draws up the Rudolphine
Tables — Galileo discovers the principle of the Pendulum — Cal-
culates the velocity of Falling Bodies, and shows why it in-
creases— Shows that Unequal Weights fall to the Ground in the
same time — Establishes the relations of Force and Weight — Sum-
mary of the Science of the sixteenth century.

Baptiste Porta's discoveries about Light, 1560. — The next
discovery in science was about Light, and it was made by a
boy only fifteen years of age. Baptiste Porta was born in
Naples ia 1545. He was so eager for new knowledge that
when quite a boy he held meetings in his house for any of
his friends to read papers about new experiments. These
meetings were called * the Academy of Secrets,' and in the
year 1560, when Porta was fifteen, he published an account of
them in a book called * Magia Naturalist or ' Natural Magic'
In the seventeenth chapter of this book he relates the fol-
lowing experiment which he had made himself

He says he found that by going into a darkened room
when the sun was shining brightly, and making a very small
hole in the window-shutter, he could produce on the wall of

CH. X.

CAMERA OBSCURA ' AND AIA GIC LANTERN. 75

the room, opposite the hole, images of things outside the
window. These images were exactly the shape of the real
objects, and had always their proper colours ; as for example,
if a man was standing against a tree outside the house, the
green leaves of the tree and the different colours of the man's
clothes would be clearly shown on the wall. There was
only one peculiarity about the picture, it was always upside
down, so that the man stood on his head, or the tree \\A\\\
its trunk in the air. The smaller the hole was, the clearer

Fig. 7.

were the outline and the colours of the image, and Porta
found that by putting a convex lens (that is, a glass with its
surfaces bulging in the centre, see p. 49) into the hole he
could get a still brighter and clearer picture at a particular
point in the room.

Porta knew from the works of Alhazen that rays of
light are reflected in all directions from every object, and he
explained this image on the wall quite correctly, by saying
that the small hole lets in only one ray from each point of an
object outside j the other rays and those from the sky and
other objects being kept out by the shutter. Thus these
single rays .fall directly on the wall without being mingled
with others, and so make a clear picture. It is easy to see
from fig. 7 that the image must be upside down, because the
rays cross in going through the hole. This simple discovery
of Porta's is called the ' Camera Obscura, or * Dark Chamber.'

76 SIXTEENTH CENTURY. pt. hi.

You may perhaps have been into one at the sea-side, where
they build them for visitors to watch the coloured reflec-
tion of the passers-by. In the camera obscura, as it is now
made, the glasses are so arranged that the figures are up-
right.

Porta saw at once how useful this" invention would be for
making accurate drawings of objects ; for, by tracing out with
colours on the wall the figure of the man or tree as it stood,
he could get a small image of it with all its proportions and
colours correct. But, what is still more important, he was
led by this experiment to understand how we see objects,
and to prove that Alhazen was right in saying that rays
of light from the things around us strike upon our. eye.
For, said Porta, the little hole in the shutter with the lens
in it, is like the little hole in our eye, which also con-
tains a natural convex lens ; and we see objects clearly
because the rays pass through this small hole. He did
not, however, know which part of our eye represents the
wall on which the figure is thrown, nor why we see objects
upright ; we shall see (p. 96) that Kepler discovered this many
years afterwards.

When Porta had succeeded in getting clear images of
real things on the wall, he began to try painting artificial
pictures on thin transparent paper and passing them across
the hole in the shutter, and he found that the sun threw a
very fair picture of them on the wall. In this way he pro-
duced representations of battles and hunts, and so made a
step towards the Magic Lantern. He seems, however, never to
have tried it by lamplight ; this was done by Kircher, a Ger-
man, about fifty years later. There is no doubt that Porta had
a ver}^ good notion of how to use two magnifying glasses so as

CH. X. DISCOVERY OF ELECTRICITY. 77

to make objects appear nearer and larger, but it is not certain
that he ever really made a telescope.

Dr. Gilbert, the Founder of the Science of Electricity,
1540-1603. — It was about this time, while Baptiste Porta
was making experiments on light in Italy, that an English-
man named Gilbert made the first step in one of the most
wonderful and interesting of all the sciences, namely, that of
Electricity. So long ago as the time of the Greeks it was
already known that amber, when rubbed, will attract or draw
towards it bits of straw and other light bodies, and it is from
the Greek word electron — amber, that our word electricity is
taken.

Until the sixteenth century, however, no one had made
any careful experiments upon this curious fact, and it was
Dr. Gilbert, a physician of Colchester, who first discovered
that other bodies besides amber will, when rubbed, attract
straws, thin shavings of metals, and other substances. You
can easily try this for yourself by rubbing the end of a stick
of common sealing-wax on a piece of dry flannel, and then
holding the rubbed end near to some small pieces of light
paper, or some feathers or bran. You will find that these
substances will spring towards the sealing-wax and cling to
it for short time, being held there by the electricity which
has been produced by rubbing the sealing-wax.

Gilbert showed that amber, jet, diamond, crystal, sul-
phur, sealing-wax, alum, and many other substances, have
this power of attraction when they are rubbed, and he also
proved that the attraction was stronger when the air is dry
and cold than when it is warm and moist. This may seem
very little to have discovered compared to the wonderful
facts which we now know about electricity ; but it was the
first step, and Gilbert's book on * Magnetism ' (as he called

78 SIXTEENTH CENTURY. pt. hi.

it), which was published in 1600, must be remembered as
the earUest beginning of the stuSy of electricity.

Tycho Brahe, Astronomer, 1546-1601. — We must now
return to Astronomy, in which during the next eighty years
wonderful discoveries were made by three celebrated men,
Tycho Brahe the Dane, Galileo the Italian, and Kepler the
German.

Tycho Brahe was born in the year 1546, at Helsinborg,
a town in Sweden, which at that time belonged to the Danes.
When he was only fourteen he was so much astonished that
the astronomers had been able to foretell exactly the
moment when an eclipse of the sun took place in 1560,
that he determined to learn this wonderful science, which
could predict events. His father had intended him to be a
lawyer, but Tycho bought a globe and books with his own
money, and studied astronomy in secret ; till at last his
family consented to let him follow his Q-^mi inclination, and
from that time he gave himself up to that science, planning
and making the most beautiful instruments for taking obser-
vations in the heavens.

At this time the theory of Copernicus had made very
little impression, and Tycho Brahe rejected it altogether
and made a theory of his own called the Tychonic system,
which was, however, soon laid aside and forgotten. This,
however, mattered very little, for the useful work which
Tycho did was not to lay down new laws, but to collect an
immense number of accurate facts which were invaluable to
the astronomers who came after him. For twenty-five years
he lived in the little island of Huen, in the Baltic, which
the King, Frederick II. of Denmark, had given him,
making accurate observations of the different movements of
the planets, and determining the positions of the fixed stars,

CH. X. ORIGIN OF THE FEADULUM. 79

of which he catalogued 777. He built there a magnificent
observatory, which he called Uranienburg, or the City of the
Heavens, and filled it with instruments of every kind, which
enabled him to keep a register of the different positions of
the heavenly, bodies night after night.

When Frederick II. died, Tycho was persecuted and
driven into exile by some envious people who grudged him
the pension he was receiving. He then went to Bohemia,
under the protection of the Emperor Rudolph II., and here
he drew up the valuable astronomical tables called the
Rudolphine tables, which, as we shall afterwards see, were of
immense use to Kepler. Tycho died ini6oi, before* Galileo
and Kepler made their greatest discoveries.

Galileo's discovery of the principle of the Pendulum,
and of the rate of Falling Bodies, 1564-1600.— Galileo dei
Galilei was born at Pisa in 1564. His father, though of
good family, was poor, but being himself a man of talent
and education, he made great exertions to send his son to
the University of Pisa, meaning to educate him as a doctor.
Here Galileo studied medicine under the famous botanist
Caesalpinus ; but having also begun to learn geometry, he
became so wrapt up in this pursuit that his father found it
was useless to check him, and therefore wisely let him follow
his natural bent. It was while he was still at the University,
and before he was twenty years of age, that Galileo made his
first discovery. When watching a lamp one day which was
swinging from the roof of the cathedral, he noticed that,
whether it made a long or a short swing, it always took the
same time to go from one side to another. To tnake quite
sure of this he put his finger on his own pulse, and, compar-
ing its throbs with each swing of the lamp, found that there
was always the same number of beats to every swing. Fol-

8o SIXTEENTH CENTURY. pt. hi.

lowing up this simple observation he discovered that a weight
at the end of a cord will always take the same time to swing
backwards and forwards so long as the cord is of the same
length and the arc through which the weight moves is small.
This was the beginning of pendulums, such as we now have
to our clocks, but at first they were only used by physicians
to count the rate at which a patient's pulse beats.

In 1589 Ferdinand de' Medici, Duke of Tuscany, having
heard of Galileo's talents, made him Lecturer of Mathematics
at Pisa, and it was while he held this post that he made his
next discovery, which was about falling bodies. He observed
that a stone or any other body, dropped from a height, falls
more and more quickly from the time it starts till it reaches
the ground, and after many experiments he succeeded in
calculating at what rate its falling increases. At the end of
the first second it will be falling at the rate of 32 feet per
second, at the end of two seconds it will be falling at the
rate of 64 feet per second, at the end of three seconds at the
rate of 96 feet per second, and so it will continue, falling 32
feet faster every second till it reaches the ground.

Galileo explained this increase of velocity, or quickness
of falling, in the following way : It is the weight of the stone,
he said, which drags it down ; and when it had been once
started downwards by its weight, it would go on moving at
the same rate for ever, without any more dragging. But the
weight still goes on pulling it down just as much at the end
of the first second as it did when it started, and so the stone
falls, first with the drag of its start, then with the drag of the
first secon<i added, then of the next, and the next all added
together, until it reaches the ground.

This was quite a true explanation, so far as it went, and
Galileo went on to prove another fact, which sounds very

en. X.- THE RATE OF FALLING BODIES. 8i

strange at first, namely, that if you let two weights, one
light and the other heavy, drop from the same height, they
will both take exactly the same time in falling to the ground.
Galileo could not make the learned men of Pisa believe
this, because Aristotle had said that a ten-pound weight
would fall ten times as fast as a one-pound weight ; so to
convince them he carried different weights up to the top of
the Tower of Pisa, and let them fall before their eyes.
Still, though they saw them reach the ground at the same
moment, they would not believe, so obstinately were they de-
termined to think with Aristotle ; and they actually annoyed
Galileo so much on account of his opinions that he left Pisa
and became a professor at Padua in 1592.

The best way for you to convince yourself that Galileo
was right and they were wrong will be to take some large
soft clay balls, say five, each exactly the same weight, and
let them drop at the same moment from the same height —
you can see at once that they will all reach the ground
together. Then press four of the balls one against the
other so that they stick together. They will now be four
times heavier than the remaining ball, and yet if you let
them drop from the same height again, there is no reason
why the four should fall any faster merely because they are
stuck together than when they were separate, and so the five
will reach the ground together as they did before. I have
said take large balls, because if they are not tolerably heavy
the air will interfere with their falling accurately ; indeed, to
make the experiment very truly it ought to be made in a
vacuum, that is, a space from which the air has been pumped
out, for it is easy to see that air, like water, will buoy up a
light body more than a heavy one, and so would cause it to
be longer in falling. But air-pumps were not invented in

82 SIXrEENTH CENTURY. it. ill.

Galileo's time, so he could not make the experiment very
accurately.

In the year 1592 Galileo established another law in
mechanics which is of great value, namely, that any force
which will lift a weight of two pounds up one foot' will lift a
weight of one pound up two feet, or in other words, just as
much as you make a weight lighter, so much higher the
same force can lift it. If you double the weight, the same
force will only lift it half as high ; if you treble the weight, it
will only lift it one-third as high, and so on. This law is of
immense value in determining the balance of machines, but
we cannot examine it further here. At about the same time
that Galileo was discovering these laws of motion, a famous
engineer, named Stevinus, of Bruges, published a little book,
in which he made known some very important laws about
the rest and motion of bodies, which formed the foundation
of the modem science of statics, or the study of bodies at
rest.

Summary of the Science of the Sixteenth Century. —
And now we must pause for a moment in the history of
Galileo, for his astronomical discoveries belong to the next
century, and before entering upon them we must reckon
up the advances which had been made in science during
the past hundred years.

I think you will agree with me that at least one grand step
had been made when men learned to examine for themselves,
and were no longer content merely to repeat like parrots what
the Greeks had handed down to them. Copernicus had
shown in astronomy, Vesalius in anatomy, and Galileo in
mechanics, that it was no longer enough to quote passages
from Ptolemy, Galen, and Aristotle j but men must take the
trouble to examine the works of nature for themselves, if

CH. X. CONCLUDING REMARKS. 83

they wished really to understand the laws of the Great
Creator.

This, in itself, was a great advance ; but beyond this
Copernicus, by his new system, had opened the way for
grand astronomical discoveries which you will see followed
quickly in the next century, and Tycho, by -his long and
patient observations, had stored up facts for the use of those
who came after him. In the same way Vesalius in anatomy,
and Gesner and Csesalpinus in natural history, had laid a
foundation for the regular study of living beings, and had
roughly sketched out a plan of classification. In the subject
of light. Porta had invented the camera obscura, explained
the principle upon which it acts, and in doing this had made
important discoveries about the action of light upon our
eye, and the use of lenses^ or convex and concave glasses,
in magnifying objects. Lastly, Galileo had discovered the
principle of the pendulum and the rate of falling bodies,
and was now on the brink of the discovery of the telescope
and all the wonders which it has revealed.

Meanwhile the sixteenth century closed with one very
sad event, which must be mentioned here. Giordano Bruno,
a Dominican friar, who was born about the year 1550, at Nola,
in Italy, was one of the first people who openly taught that
the Copernican system was true. He ought to be peculiarly
interesting to us, because he was the first person to teach in
England that the earth moves round the sun. But poor
Bruno was a very plain outspoken man, and his bold
language brought him to a sad but noble death. When
people said he should not spread the Copernican system
because it was contrary to the Bible, he answered boldly
that the Bible was meant to teach men how to love God
and live rightly, and not to settle questions of science.

84 SIXTEENTH CENTURY. pt. in.

Most people now would say that Bruno was right, but the
judges of the Inquisition did not think so, and were so
alarmed at his opinions that they condemned him to death.
In the year 1600, just after the century closed, Bruno was
burnt at the stake in Rome as an atheist, partly because he
insisted on repeating that the earth is not the centre of the
universe, and that there may be other inhabited worlds be-
sides ours.

Chief Works consulted. — Whewell's * Inductive Sciences ; ' Brewster's
'Optics;' Brewster's 'Martyrs of Science,' 1874; 'Encyclopaedia
Britannica,' art. ' Astronomy ; ' Drinkwater's * Life of Galileo ; '
Rossiter's * Mechanics,' 1873 ; Cuviei", * Histoire de Sciences Natu-
relles ; ' Baden Powell's ' Natural Philosophy.*

SCIENCE OF THE
SEVENTEENTH CENTURY

Chief Men of Science in the Seventeenth Century,

A,D.

Galileo 15 64- 1642.

Kepler

.

.

15 71-1630.

Gassendi .

1592-1655.

Horrocks .

1619-1641.

Newton

1 642- 1 72 7.

Halley

1656-1742.

Francis Bacon .

1561-1626.

Descartes .

1596-1650.

Snellius

1591-1626.

Drebbel .

I 5 72-1634.

Torricelli .

1 608-1 647.

Guericke .

1 602-1 686.

Boyle

1626-1691.

Hooke

I 635-1 702.

Huyghens .

, 1629-1695.

Roemer

. 1644-17 10.

Mayow

. 1645-1679.

Beeclier

. 1625-1682.

Stahl

. 1 660-1 734.

Steno

. 1638-1687.

Scilla

. I 639-1 700.

Woodward

. 1661-1727.

Harvey

. 1578-1657.

Asellius

. . 1581-1626.

RUdbeck .

. 1 630-1 702.

Malpighi .

. 1628-1694.

Leeuwenhoeck

. 1632-17^3.

Grew

. 1628-1711.

Ray .

. 1 628-1 705.

Wniughby

. 1635-1672.

CH. XI. GALILEO. 87

CHAPTER XL

SCIENCE OF THE SEVENTEENTH CENTURY.

Astronomical discoveries of Galileo — The Telescope — Galileo esamines
the Moon, and discovers the Earth-light upon it — Discovers Jupiter's
four Moons — Distinguishes the Fixed Stars from the Planets — The
phases of Venus confirm the Copernican theory — Galileo notices
Saturn's Ring, but does not distinguish it clearly — Observes the
spots on the Sun — The Inquisition force him to deny the movement
of the Earth — Blindness and Death of Galileo.

Astronomical Discoveries of Galileo, 1609-1642. — The seven-
teenth century was not many years old when Galileo startled
the world with discoveries such as had never been heard of
before. He relates that when quite a young man he was so
struck with an account given by some of his companions of
a lecture on the Copernican theory, that he determined to
study it, and he soon became convinced of its truth. Never-
theless he saw how difficult it would be io prove that the earth
moves round the sun, and not the sun round the earth.

When he went to Padua he gave a great deal of time to
the study of astronomy, and had already made some
remarkable observations, when one day, in the year 1609,
being in Venice, he heard that a Dutch spectacle-maker had
invented an instrument which made distant things appear
close at hand.

This discovery, which Bacon and Porta had foreseen,
was made at last almost by accident in Holland, by two
spectacle-makers, Zacharias Jansen and Henry Lippershey.

88 SEVENTEENTH CENTURY, ft. hi.

It is related that Jansen's children when playing one day with
two powerful magnifying glasses, happened to place them
one behind the other in such a position that the weathercock
of a church opposite the house seemed to them nearer and
larger than usual, and their father, when he saw this, fixed
the glasses on a board and gave them as a curiosity to
Prince Maurice of Nassau. -Whether this story be true or
not, it is certain that in the year 1609, both Jansen and
Lippershey made these rough telescopes as toys, though they
did not know how useful they might be. But when Galileo
heard of it he saw at once what valuable help it might
afford in studying the heavens ; and he set to work imme-
diately, and soon succeeded in making a useful instrument.
A diagram of Galileo's telescope is given in Fig. 8. It
was made on the same principle as opera-glasses are now,
with one convex lens a b, which makes the rays from the
object bend inwards or converge, and one concave \^Vi.s Q, d,
which makes them bend outwards or diverge before they
come to a focus. In Fig. 8 one complete cone of rays is
drawn coming from the point in, and the outline of another
cone from the point n j there are really similar cones coming
from all points along the arrow, but it is impossible to give
these in a diagram. Each set of rays as they fall on the
lens A B, are made to converge, so that they would end in a
point or focus, if they were not caught by the lens c d. But
this lens having its surfaces curved inwards makes the rays
bend outwards or diverge again, so that the end of the cone m
reaches the eye in parallel lines at m' m' and the cone n at
n' n'. From here, as you will remember (see p. 49), we
follow them out in straight lines, and see the image at the
angle m ^ n, so that it appears greatly magnified. If you
look at any object through ome tube of an opera-glass, and

CH. XI.

GALILEOS TELESCOPE.

89

keep the other eye open so as to see the object at its natural
distance, you can cover the real image with the magnified
one, and thus see the magnifying power of your glass. But
when you do not compare them in this way you do not
realise how much the object is enlarged, because it appears

Fig. 8.

Galileo's Telescope.

A B, Convex lens ; C D, concave lens next the eye ; ni n, real arrow ; M N,
apparent size of arrow ; tn' m' and n'n', end of the cones of rays m and n as
they reach the eye ; M <? n, angle at which the magnified arrow is seen.

to come nearer, so as to be at some point between m n
and 0, and to be less magnified in consequence. I must
warn you that both in this diagram and the one at p. 97
the proportions are very much distorted, because a star or
even a house would be an immense distance oif as compared
with the length of a telescope, whereas the arrow is obliged
to be drawn here as near to the lenses as they are to each
other.

Secondary Light of the Moon. — Galileo's first telescope
only magnified three times, that is, made an object three
times larger ; but he made a second which magnified eight
times, and then he turned it to the moon and began to

90 SEVENTEENTH CENTURY. pt. iii.

examine the surface of that sateUite. He saw the mountains
_of the moon^_aiidjhe_deepJi^^

the wids plains which he mistook__fbi^^oceariSi__Then he
noticed that curious light" calTed the secondary light, which
jtnay be seen on the dark side^^ofjhe^maon arherL-on^L-one
quarter~oriFis'^right; and shining. Gahleo discovered that
this"curious figEFTs a reflection from the earth j for you must
know that we reflect the sun's Hght back to the moon just in
the same way as the moon does back to us, and at the time
when we see a new moon, the man in the moon (if there
were such a person) would see a large full earth and could
wander about at night by earth-light as we do by moonlight.
Look up at the new moon just about dusk in the evening,
and if it is a clear night you will most likely be able to see
a faint outline of the dark side of the moon, which is
caused by our earth-light shining upon it.

Jupiter's Moons. — When Galileo had studied the moon
and gazed with intense delight on the myriads of tiny stars
in the Milky Way, he next turned his telescope to the planet
Jupiter. To his great surprise he saw three small shining
bodies like stars close to Jupiter which were quite invisible to
the naked eye. Tw^o of them were on the east side of the
planet and the other on the west. He waited eagerly for the
second night, to see if Jupiter would move away from these
stars, but he found them still together, only the two stars
which had been on the east side had now moved round to
the west, and they were nearer to each other than they had
been before. He was quite puzzled as to how this could
have happened, and watched and watched for many nights
whenever the clouds would allow him ; and at last, on the
fourth night after he had first seen them, he came to the
conclusion that all three stars were moving round and round

CH. XI. ASTRONOMICAL DISCOVERIES. 91

Jupiter, as the moon goes round our earth. A few nights
later he found that there was a fourth star which went round
with them ; and so Gahleo discovered Jupiter's four moons
in the year 16 to.

This was the first fact in favour of the Copernican theory
which ordinary people could understand. The planets had
till now been looked upon simply as lights in the sky moving
round the earth ; but now it could not be doubted that
Jupiter at least was something more than this, for he had a
system like our own, with four moons, to give him light by
night, instead of one. As usual there were a great number
of people who were alarmed at the fact that our little earth
should not be the central body in the heavens, and many
astronomers would not believe that Galileo had really seen
Jupiter's moons ; one was even so foolish as to refuse to
look through the telescope, for fear he should see them.

Phases of Venus. — Galileo, however, now felt sure that
his new instrument would help him to read wonderful truths
in the beautiful universe of God, and he threw his whole heart
and soul into this grand study. It was not long before he
discovered another proo£jthat the planets move round the
sun and not round the earth. When he first saw the planet
Venu^hrougLthe..tel£scape-she was .rounds but happening
to Jook_ at .her one day when she was almost between the
earth and the sun, he sawherjnjhe form of a crescent like a
newimoon. Struck by this, he continued to observe her night"
after night till she had made the whole journey round the sun,
and he proved to himself that she went through the same
changes as our moon, from a crescent shape to a full round
face. This was just what she would be expected to do if she
and we both travelled round the sun. Thus for the second

92

SEVENTEENTH CENTURY. pt. hi.

time Galileo proved that the Copernican theory was the true
one.

He next turned his attention to Saturn, and before the end
of the year he had made out that this planet was not single,
but had something on each side of it which he thought were
two small stars. This was Saturn's ring, but GaHleo's tele-
scop.ejKas_nat„p£t^er£iiLjeiLQUgh„fcr,Hn^^ ^Ih

the year 1659 another famous astronomer, named Huyghens,
saw the ring through a much better telescope, and described
it (see Chapter XXI.).

Sun-spots. — Galileo had now a great wish to go to Rome,
so that he might show the new wonders he had discovered
to the learned men who lived in that city. He accordingly
carried his telescope there in 1611, and set it up in the
Quirinal Garden. It was there that he first noticed the dark
spots on the face of the sun, and observed that they were
not always of the same shape, but that two or three would
sometimes run into one, or that one would divide itself into
three or four. These spots, which even now puzzle astrono-
mers, were observed by several other men, especially by an
English astronomer named Harriot, about the same time as
by Galileo. But Galileo made a special use of his discovery,
for he pointed out that the spots moved round regularly in
about twenty-eight days, disappearing on one side of the
sun and reappearing after some time on the other. This
proved that the sun turns round upon its own axis in twenty-
eight days.

Galileo before the Inquisition. — And now we come to
the sad part of Galileo's history. He was well received in
Rome, and the Pope even gave him a pension of a hundred
cro^vns ; but the judges of the Inquisition, who had caused

CH. XI. GALILEO IN ROME. 93

Bruno to be burnt alive, became uneasy that Galileo should
teach so many new things, and especially that he should,
prove that our earth was not the centre of everything, but a
mere speck among the numberless stars and planets in the
heavens. They therefore sent for Galileo, in the year 1616,
and threatened to punish him unless he would promise to
hold his tongue about this new theory. Galileo, however,
would not* be silent ; surrounded by his little circle of admir-
ing pupils, he could not refrain from spreading wherever he
went the grand facts he had discovered and the truths they
taught. He was impatient that the world should not see as
clearly as he did how glorious the universe is when rightly
understood, and he often spoke and wrote sharply and sar-
castically of those who would not listen to truth.

At last, in 1632, he wrote a book called ' The System of
the World of Galileo Galilei,' in which he clearly proved the
truth of the Copernican theory, and alluded very angrily to
the attempt which the Inquisition had made to force him to
be silent. This book convinced many people, but at the
same time it roused the anger of the judges of the Inquisi-
tion. They summoned Galileo (then an old man seventy
years of age) to appear again before them ; and this time
they made him kneel, clothed in the sackcloth of a penitent,
and swear with his hands upon the Gospels that ' it was not
true that the earth moved round the sun, and that he v,'ould
never again in words or writing spread this damnable
heresy.' It is very sad to think that Galileo should thus
swear to what he knew was a lie ; but it is still more sad
that men holding their power in the name of God should
force him to choose between telling a lie or being put to
torture or to death as Giordano Bruno had been. When

94 SEVENTEENTH CENTURY. pt. hi.

Galileo rose from his knees it is said that he stamped his
foot and whispered to a friend : ^ E pur si muove^ (' Never-
theless it does move ') .

After a time he was allowed to go back to his own home,
but never again to leave it without the Pope's permission.
He went on with his studies, and made many useful obser-
vations j but in the year 1636 his sight began to fail, and he
soon became totally blind. At this time he wrote to an
acquaintance these touching words : ' Alas ! your dear friend
and servant has become totally and irreparably blind. These
heavens, this earth, this universe, which by wonderful obser-
vation I had enlarged a thousand times beyond the belief
of past ages, are henceforth shrunk into the narrow space I
myself occupy. So it pleases God, it shall therefore please
me also.' He died January 28, 1642, in his seventy-eighth
year ; having accomplished his work. In spite of all oppo-
sition, his discoveries had firmly established the truth of the
Copernican system of the universe.

Chief Works consulted. — Brewster's ' Martyrs of Science ; ' Drink-
waters * Life of Galileo ; ' Herschel's ' Astronomy ; ' Whewell's
'Inductive Sciences ;' ' Enclyclopaedia Britannica,' art. 'Astronomy ;'
Baden Powell's * Hist, of Natural Philosophy;' Ganot's 'Physics,'
edited by Atkinson.

CH. XII. THE RUDOLPHINE TABLES. 95

CHAPTER XII.

SCIENCE OF THE SEVENTEENTH CENTURY (CONTINUED).

Kepler the German Astronomer — Succeeds Tycho as Mathematician
to the Emperor Rudolph — His description of the Eye — He tries to
explain the orbit of the planet Mars — And by comparing Tycho's
tables with observation discovers his First and Second Law of the
movements of the Planets — His delight at Galileo's discoveries —
Kepler's Third Law — Comparison of the labours of Tycho, Galileo,
and Kepler.

Kepler, 1571-1630.— While Galileo was occupied in dis-
covering unknown worlds with his telescope, another famous
astronomer, named Johannes Kepler, was working out three
grand laws about the movements of the planets. John
Kepler was born in 1571. His parents, though noble, were
poor, and always in difficulties, but in spite of all obstacles
he managed to educate himself, and even to take his degree
at the University of Tubingen. In 1594 he was made Pro-
fessor of Astronomy at Gratz, in Styria, and while there he
began his attempts to discover the number, size, and orbits
of the planets, but at first with no success. In 1597, when
the Catholics at Gratz rose against the Protestants, Kepler,
being a Protestant, was forced to leave the city, and would
have been in great difficulties if his friend Tycho Brahe
had not invited him to come to Prague as his assistant
in the observatory. Here Kepler worked with Tycho at
his astronomical tables, called the ' Rudolphine Tables,'
in honour of the Emperor Rudolph ; and when Tycho died,

96 SEVENTEENTH CENTURY. Fr. ill.

in 160T, he succeeded him as principal mathematician to
the Emperor.

Kepler on Optics, 1604. — Although Kepler is chiefly
known as an astronomer, his first work, published in 1604,
was on Optics, and in it he points out most beautifully the
true use of the different parts of the eye. He was much
struck with Porta's idea that the eye is like a camera obscura,
and he proved that the rays of light, after passing through the
lens of the eye, form a real picture upside down on the fine
network of nerves called the retina, at the back of the eye,
and are then conveyed by the optic nerve to the brain. He
also pointed out that the reason why we do not see things
upside down is that since our mind follows out each ray in a
straight line, the rays appear to cross back again on the lens
of the eye, and we see them as if they had never been in-
verted. This is, however, a question still undecided by
physiologists.

Kepler invented a much more powerful telescope than
the one which Galileo had made. You will see by turn-
ing back to p. 88 that the fault of Galileo's telescope was that
it made the rays diverge or bend outwards, just as they
reached the eye, and in this way many of them passed out-
side and were lost. Kepler avoided this by using two convex
lenses. In his telescope (see Fig. 9), the rays firom the object
771 n, after converging on the lens a b come to a focus at 7n' n',
where they make a real image of the arrow upside down. If
you. could put a piece of thin transparent paper at the pomt
7n' 7i' in a telescope, you would see a picture of the object
upon it. The rays from this image falling on the lens c d,
are again bent inwards, as by the ordinary magnifying glass
(see p. 49), and thus by following them out in straight lines
the eye sees a niagnified arrow upside down at some point

CH. XII.

KEPLER'S '7HREE LAWS:

97

between c d and m n. Kepler's telescope is called the
' Astronomical telescope.' It has a much larger 'field of
view ' than Galileo's ; that is, it enables you to see over a
larger space at one time ; but, on the other hand, it turns

Fig. 9.

Kepler's Telescope.'

A B, Object glass, c d. Eye-piece, m n. Real arrow, m' n'. Picture of the arrow
formed at the focus of the rays, m n, Magnified arrow.

everything upside down. In making astronomical observa-
tions it is not of much importance which part of a star is
uppermost ; but for terrestrial telescopes another lens has to
be put in to bring the images back to their right positions,
and since Kepler's time many other improvements have been
made.

Kepler's first Law, 1609.— After Tycho Brahe's death
Kepler went on working at the ' Rudolphine Tables,' and
this led him to consider again the movements of the planets,
and to try and find a theory to explain the path or orbit of
the planet Mars. Mars is the planet which stands fourth
from the sun ; thus Mercury is nearest to the sun, then

' This figure and also fig. 8 were kindly drawn for me by Mr. A. R.
Wallace.

6

98 SEVENTEENTH CENTURY. pt. in.

comes Venus, then our earth, and then outside our earth is
Mars. Tycho had noted in his tables the places at which
the planet had been seen at certain periods ; and from these
observations Kepler calculated where it ought to arrive at
other fixed times if it moved in a circle, as the earlier
astronomers had supposed. But he found that it did not
arrive there as computed, and he was so sure that Tycho's
observations were exact that he said boldly, ' All the theories
must be wrong if they do not agree with what Tycho saw.'
So he puzzled on, trying one explanation after another, until
at last he discovered three remarkable laws, by which the
movements not only of Mars, but of all the other planets,
are explained.

The first of these laws is that planets move round the
sun in ellipses or ovals, and not in circles. You know that
to draw a circle you put one leg of the compasses into a
spot and draw the other leg round it, and the middle spot
is called the centre or focus. But to draw an ellipse you
must have two focuses or foci. To understand this, stick
two pins a little distance apart in a piece of paper, and
fasten a string to them by its two ends. Place a pencil
upright in the string, so as to keep it tightly stretched, and
draw the pencil round first on one side then on the other.
You will then have an ellipse, and the two pin-holes will be
the two foci. Draw the sun in one of the foci and a round
globe on some part of the ellipse, and you will have a figure
of the path of our earth or any of the planets round the sun.
You will find that the farther you put the pins apart the
flatter the ellipse will be. The path or orbit of the planet
Mercury is much more elliptical than the orbit of the Earth.
Another difference in the orbits of the planets is that they
do not all lie in the same direction, though they all have the
sun as one of their foci. For instance in Fig. lo, the orbit

CH. XII.

KEPLER'S 'THREE LAWS:

99

of the planet a has the sun for one focus and the dot c for '
the other, while the orbit of the planet b has the sun for one
focus and the dot d for the other, and this makes the two
orbits lie in a different di-

FlG. lO.

rection. Kepler's first law,
then, was SkidX planets move
in ellipses.

Kepler's Second law,
1609. — His second law was
about the rate at which
planets move. He found
from Tycho's tables that
they all moved more

quickly when they were near the sun than when they were
far from it, and after an immense number of calculations
he found the following rule. If you could draw a line from
the sun to any planet on the first day of each month of
the year, you would enclose
a number of spaces, such
as ^, by c, d, &c., in Fig. 1 1,
and each of these spaces
would be the same size,
although not the same
shape. For instance, the
planet, when travelling from
I to 2 near the sun, would
go very quickly and pass
over a number of miles,

while when travelling from 6 to 7 it would go slowly and
pass over comparatively few miles. And yet the space /
will be exactly the same size as the space a, only it will
be long and thin instead of short and broad. Kepler's

loo SEVENTEENTH CENTURY. pt. hi.

second law, therefore, was that planets describe equal areas
about their centre in equal times.

Not many months after Kepler published these two
laws, he heard of Galileo's discoveries with his telescope —
that Jupiter had four satellites, and that Venus was proved
to move round the sun by having phases like our moon.
You may imagine how delighted he was to find the Co-
pernican theory made so much more certain, and to see
that the telescope was opening the way for so many new
discoveries. *Such a fit of wonder,' he said, 'seized me
at this report, and I was thrown into such agitation, that
between the joy of the friend who told me, my imagination,
and the laughter of both, confounded as we were by such
a novelty, we were hardly capable, he of speaking or I of
listening.'

For many years after this Kepler w^as beset with troubles.
The Emperor, being at war with his brother Matthias, had no
money to spare for salaries. Kepler was thus harassed by
poverty ; his favourite son died of the small-pox, which the
troops had brought into the city, and his wife died of grief
not long afterwards. It was not till the year 1618, after he had
re-married and had been rescued from his poverty by the
new Emperor Matthias, that the unfortunate astronomer had
energy and leisure to turn again to his favourite planets.

Kepler's Third Law, 1618. — It was in that year that he
worked out with immense labour his third and most famous
law — by which he showed how much longer the planets were
going round the sun, according as they were farther off
from it. This is difficult to understand, but we must try to
form some idea of it. He did not know in figures how far
each planet was from the sun, but he knew the proportion of
their distances, as for example, that Mars is 4 tirnes and

CH. xn. TYCHO BRAHE, GALILEO, AND KEPLER. loi

Jupiter 13J times farther off from the sun than Mercury,
and he also knew how long each one was in going round the
sun, and from these two facts he worked the following rule.

If you take any two planets and cube their distances from
the sun and then square the time each takes in going round
the sun, the two squai^es of the time will bear the same pro-
portion to each other as do the two cubes of the distance.
For instance. Mars is 4 times as far from the sun as Mer-
cury, and therefore it is 8 times as long going round it, be-
cause the cube of 4 (or 4 x 4 x 4) is 64, and the square
of 8 (or 8 X 8) is also 64. Thus the cube of Mercury's dis-
tance as compared with that of Mars is i to 64, and the
square of their periodic times of going round is also as
I to 64. This law holds equally true of all the planets, and
is expressed in scientific language thus : ' The squares of the
periodic times of the planets are proportional to the cubes of their
distances.

These three laws of Kepler were very great discoveries;
especially the last one, which cost him years of labour and
calculation. He was so astonished and delighted when he
proved it, that he told a friend he thought at first it must
be only a happy dream that he should have succeeded at
last after so many failures.

After this Kepler wrote and published many books, but
he made no more important discoveries. The Rudolph-
ine Tables were at last published in 1628, and Kepler
received a gold chain from the Grand Duke of Tuscany
for his services to Astronomy ; but still he could not ob-
tain the payment of his salary, and money difficulties
pressed upon him. His anxiety threw him into a violent
fever, and he died in 1630 at sixty years of age.

Work done in Science by Tycho Brahe, Galileo, and

I02 • SEVENTEENTH CENTURY. pt. hi.

Kepler. — It will be instructive to notice here how very dif-
ferent these three astronomers, Tycho, Galileo, and Kepler
were, and yet how they each did their own part to add to
our knowledge. Tycho was a man who collected facts : his
work was dry, and his tables a mass of figures, such as most
people would think very uninteresting; yet if Tycho had not
spent his life in this dry conscientious work, Kepler could
never have discovered his laws. Galileo was a warm-
hearted enthusiastic observer : he loved the beauty of the
heavens, and knew how to make others love it too j every
observation he made he told in popular language to the
world, and taught people the truth of the Copernican theory*
by showing them plainly how they could prove it for them-
selves, if they chose to look at the heavens. Kepler was
quite different from either Tycho or Galileo ; he was a m.a-
thematician, and worked everything out in his own brain by
accurate methods. He took Tycho's observations, which he
knew were true, and turned them this way and that way,
working out now one calculation, now another, and always
throwing them aside if they were not exactly true. He spent
years over his attempts, but it was worth while, for he
arrived at three true laws, which will remain for ever. There
was only one point he had not reached \ he knew that his
laws were true, but he did not know why they were true.
This was left for Newton to demonstrate nearly fifty years
afterwards.

Chief Works consulted. — Brewster's 'Martyrs of Science;' Herschel's

* Astronomy ; ' Denison's ' Astronomy without Mathematics ; ' Airy's

* Popular Astronomy ; ' Drinkwater's ' Life of Kepler ; ' Baden
Powell's * History of Natural Philosophy.'

CH. XIII. FRANCIS BACON.— ' NOVUM ORGANUM: 103

CHAPTER XIII.

SCIENCE OF THE SEVENTEENTH CENTURY (CONTINUED).

Francis Bacon, 1561-1626 — He teaches the true method of studymg
Science in his 'Novum Organum' — Rene Descartes, 1596-1650 —
He teaches that Doubt is more honest than Ignorant Assertion —
Willebrord Snellius discovers the Law of Refraction, 1 62 1 —
Explanation of this Law.

Bacon's Influence upon Science.- — Although this book
is a history of scientific discovery and not of philosophy,
yet we must now mention in passing two philosophers who
lived about this time, and whose writings had great in-
fluence upon science. These were Francis Bacon in Eng-
land, and Rene Descartes in France.

Francis Bacon, commonly known as Lord Bacon, was
born in London in 1561, and died in 1626. He was made
Lord Chancellor of England in 16 18, in the reign of
James I., with the title of Lord Verulam and afterwards
Viscount St. Alban's, and was a great political character.
Bacon devoted much of his time to science, and, like his
namesake Roger Bacon in the fifteenth century, he seems to
have foreseen many of the discoveries which were afterwards
made. But his most useful work was a book called the
'Novum Organum,' or 'New Method,' published in 1620,
in which he sketched out very fully how science ought to be
studied. He insisted that no knowledge can be real but
that which is founded on experience, and that the only

I04 SEVENTEENTH CENTURY. ft. iit.

true way to cultivate science is to be quite certain of each
step before going on further, nor to be satisfied with any-
general law until you have exhausted all the facts which it is
supposed to explain.

For example, if you require to understand what heat is,
and how it acts, you must not be satisfied, he says, by
merely making a few experiments on the heat of the sun and
that of fire, and trying from these to lay down some general
rule of how heat works. ' No, you must examine it in the
sun's rays both when they fall direct and when they are re-
flected j in fiery meteors, in lightning, in volcanoes, and in
all kinds of flame ; in heated solids, in hot springs, in boil-
ing liquids, in steam and vapours, in bodies which retain
heat, such as wool and fur j in bodies which you have held
near the fire, and in bodies heated by rubbing; in sparks
produced by friction, as at the axles of wheels ; in the heat-
ing of damp grass, as in haystacks ; in chemical changes, as
when iron is dissolved by acids j in animals ; in the effects
of spirits of wine ; in aromatics, as for example pepper,
when you place it on your tongue. In fact, you must study
every property of heat down to the action of very cold water,
which makes your flesh glow when poured upon it. When
you have made a list,' says Bacon, ' of all the conditions
under which heat appears, or is modified, of the causes
which produce it, and of the efiects which it brings about,
then you may begin to speak of its nature and its laws, and
may perhaps have some clear and distinct ideas about it.'

You will see at once that this method of Bacon's had
been followed already to a great extent by Copernicus,
Tycho Brahe, Galileo, and Kepler ; but Bacon was the first
to insist upon it as the only rule to follow, and in doing this
he rendered a great service to science.

CH. XIII. WRITINGS OF DESCARTES. 105

Descartes' Condemnation of Ignorant Assertion.' — Rene

Descartes, by his philosophy, assisted science in another way.
He was a Frenchman, born in Touraine in 1596, and he
became one of the most famous philosophers of France. He
wrote a great deal on science, especially on mathematics and
geometry, and also on the nature of man ; but the point
which we have to notice here was his belief that to arrive at
the real truth was the only thing worth living for.

You will remember how the men of science of the
sixteenth century had thought it a sufficient answer to Vesa-
lius or to Galileo to say that Galen or Aristotle had decided
questions of anatomy and physics ages ago ; and how the
judges of the Inquisition thought they had crushed the Co-
pernican theory when they made Galileo recant. Authority
was the idol to which these people bowed down, and they
considered it rank heresy to doubt anything which had been
taught by their forefathers. But Descartes said, ' It is not
true to say we know a thing simply because it has been told
us. It is a duty to obey authority, to submit to the laws and
religion of our country and parents, and in matters where
we are not able to judge, it is wise to receive what is told
us by those who know more than we do. But to know
anything requires more than this, and unless the reasons
for any belief are so clear to our minds that we cannot doubt
them, we have no right to say we knotu. it to be true^ but
only that we have been told so.'

I think you can see how this rule of Descartes, that it is
often more honest to doubt than to be quite sure without
good grounds, would influence science. If scientific men iri
the time of Galileo, instead of saying ' We k?iow that a heavy
weight falls more quickly than a light one because Aristotle
said so,' had said more modestly, ' We do not know^ because

io6 SEVENTEENTH CENTURY. pt. iii.

we have never tried, but we think it probable Aristotle was
right until someone shows us that he was mistaken ; ' — if they
had gone to the Tower of Pisa in this spirit, they would not
have denied the truth of Galileo's experiment when it suc-
ceeded before their very eyes. And even now, in the
present day, you will see that the greatest and best men who
make the most discoveries, are those who are always willing
to examine a new fact, even though it may contradict much
that they have held before ; and who never pretend to know
for certain anything which they have not studied with
sufficient care to be convinced of its truth.

These last few pages may be rather difficult for you to
follow, but the chief lessons which it is necessary you should
remember may be summed up in a few words. Bacon and
Descartes both did great service to Science — Bacon by
teaching that any true theory must be built up upon facts
and careful experiments ; Descartes by insisting that it is
more honest to acknowledge we are ignorant, and to wait
for more light, than to pretend to know that which we have
not clearly proved.

Snellins Discovers the Law of Refraction, 1621. —
Among other things, Descartes wrote much upon Optics, and
you will often see it stated that he discovered the law of
refraction. This law had, however, been laid down before,
in 162 1, by a Dutch mathematician named Willebrord
Snellius, and Descartes only stated it more clearly. You
will remember that the Arab Alhazen first pointed out that
rays of light are bent or refracted when they pass from a
rarer into a denser substance or medium (see p. 47), as for
instance from air into water; and that the denser the
medium is into which they pass the more the rays are re-
fracted. Vitellio and Kepler had measured some of the

CH. XIII.

THE LAW OF REFRACTION.

107

angles at which rays are refracted in water and glass, but
they did not know of any law by which they could calculate
how much any particular ray would be bent out of its course.
For instance, m Fig. 1 2, suppose w w to be the surface of
water in a glass vessel, upon which the rays a and b fall at

B

Measurement of Refjraction in Water.

w w, Water, a a', b b', Rays passing from air into water, d d , Line from the ray a
to the perpendicular x' , in the water, three-fourths the length oi c c from the ray A
in the air. d dJ , d d, Similar lines from the ray b.

the point o, and are refracted a to a' and b to b'. " It is evi-
dent that B is bent much more out of its course than a, as
you will see at once if you lay a straight ruler from end to
end of each ray ; and if we were to draw other rays between
these they would all be refracted at different angles, those
being most bent which were farthest from the perpendicular.
Now in making telescopes it is very important to know
how much each ray is refracted j and as the rays are infinite
in number, it was impossible to know this unless some

io8 SEVENTEENTH CENTURY. pt, hi.

general rule could be found. Snellius set himself this task,
and after a great number of very delicate experiments he
arrived at a law which has proved to be always true. This
law is best explained by the following experiment, which is
not difficult to understand although it is troublesome to per-
form it accurately.

Draw a circle on a black board with an upright line x x'
through it, and then place the board upright in a vessel of
water so that the surface of the water crosses the centre o.
Then pass a ray of light through a tube so placed that the
ray falls across the board in the direction a ^ ; it will then
pass on through the water to some point a'. The line o a
will now cut the circle at the point c, and the line o a' will
cut it at c'. From these two points draw horizontal lines c c
and dd on the board to the upright line x x'. Then if you
compare the length of these two lines you will find that d d
in the water" is exactly three-fourths of ^ <r in the air.

Again, if you throw the light from your tube in the direc-
tion B 0, the result is the same. The length of d' d' in the
water will again be three-fourths of d din the air. And this
is equally true of all rays passing from air into water. When
a vertical line is drawn through the point where the ray falls
on the water, ^/le two horizontal lines drawn to the place where
the circle cuts the ray will always be in the same propoi'tion,
at whatever angle the ray strikes the water. Therefore, f ths
is said to be the index of ref7'action for water, meaning that
every ray which passes from air into water will have these
two horizontal lines in the proportion of 4 to 3. In passing
from air into glass they would always be in the proportion
of 3 to 2, and every different substance, such as ice, amber,
diamond, &c., has its own angle of refraction. These have
been calculated, and tables made, from which you can learn

CH. XIII. REFRACTION EXPLAINED. 109

at once what is the index of refraction for any particular
substance.

It was this law of the proportion between the two hori-
zontal lines in the air and in the denser substance which
Snellius discovered. It is expressed in mathematical lan-
guage, thus : ' The ratio between the sines of the ificident and
refracted rays is always the same for the same substance ; '
sine being a mathematical term for the measurement we have
been making, which you will understand more fully when
you have studied trigonometry.

Chief Works consulted. — Herschel's ' Study of Natural Philosophy ;'
Lewes's 'Biographical History of Philosophy;' Cuvier, 'Hist, des
Sciences Naturelles ; ' Bacon, 'Novum Organum;' Huxley on 'Des-
cartes,' Macmillan's Magazine; 'Encyclopaedia Metropolitana,' art.
'Light J ' Herschel's 'Familiar Lectures,' art. 'Light.'

no SEVENTEENTH CENTURY. pt. iii.

CHAPTER XIV.

SCIENCE OF THE SEVENTEENTH CENTURY (CONTINUED).

Fabricius Aquapendente discovers Valves in the Veins — Harvey's dis-
covery of the Circulation of the Blood — Discovery of the Vessels
which carry nourishment to the Blood — Gaspard Asellius notices
the Lacteals — Pecquet discovers the Passage of the fluid to the
Heart — Riidbeck discovers the Lymphatics.

Harvey's Discovery of the Circulation of the Blood, 1619.

— In the year 1600, when Galileo and Kepler were still at
the beginning of their discoveries, a young Englishman of
two-and- twenty, named Harvey, who was bom at Folkestone
in 1578, went to Padua to study anatomy under the famous
professor Fabricius Aquapendente. Although anatomists
had by this time learnt a great deal about the bones and
parts of a dead body, yet they were still very ignorant about
the working of a Hving one. They knew that arteries throb,
like the pulse in the wrist, which is an artery ; and that veins
(that is, the blue branching tubes which you can see under
the skin in your hand and arm) contain blood and do not
throb like the arteries, but they had no clear idea of the use
of either arteries or veins. Vesalius had believed, like
Aristotle, that the arteries contained chiefly a kind of air
called ' vital spirits,' which they carried from the heart to all
parts of the body ; and that the blood was pumped back-
wards and forwards from the veins to the heart by the act of
breathing. A Spaniard named Servetus, an Italian named

CH. XIV. THE CIRCULATION OF THE BLOOD. iii

Columbus, and the botanist Cassalpinus, who all lived in
the sixteenth century, had indeed suggested that blood from
the heart flowed through the lungs (or the part we breathe
with), and came back again to the heart ; and Caesalpinus
had even noticed that if you tie up a vein it swells on the
side of the bandage away from the heart ; but the notions
of all these men were very vague and unsatisfactory.

The subject remained quite obscure till, while Harvey
was studying at Padua, his master Fabricius discovered that
many of our veins have curious valves inside them, made
by the folding of the lining of the vein. These valves, which
are just like little transparent pockets, lie open towards the
heart so long as the blood is flowing in that direction ; but
if you press on a vein — in your arm for instance — and
force the blood away from the heart towards the fingers, the
valves close at once, and the vein swells up because the
blood cannot flow on.

Fabricius thought that the, use of these valves was merely
to prevent the blood escaping too quickly into the branches
of the vein ; but this explanation did not satisfy Harvey, and
he determined to try to discover which way the blood
moved in the different vessels which held it In order to do
this he laid bare the artery of a living animal, say in its leg,
and tied it round tight, so that the blood could not flow past
the bandage. He found that the artery became very full of
blood and throbbed strongly above the place where he had
bound it, but in the lower part of the leg it did not throb
at all. This proved to him that the blood in the artery was
flowing from the heart to the leg of the animal, and was
stopped on its way down by the bandage. He then tied up
a vein in the same way, and this time the swelling was in
the lower part of the leg, bebiv where the vein was tied.

ti2 SEVENTEENTH CENTURY. pt. ill.

Therefore it was clear that the blood in the vein was flowing
from the leg to the heart, and was stopped from flowing up-
wards by the bandage. When he tied an artery and a vein
in the arm the same thing happened ; the blood in the
artery was flowing towards the hand, while in the vein it was
flowing _;9'<?m the hand towards the heart.

This led Harvey to suspect that the blood is always
making a continuous journey round and round, first out of
the heart through the arteries to all parts of the body, and
then back through the veins to the heart again. And now
the use of the little valves became evident. While the blood
flows, as it should do, towards the heart, they lie open and
offer it no resistance, but directly anything drives it in the
v/rong direction they close at once, and prevent it from
flowing backwards. The throbbing of the arteries was also
explained by this theory, for the blood being pumped into
them by a regular movement of the heart, they swell at each
rush of blood, and contract again before the next, and so
rise and fall in exact time with the beating of the heart.

Harvey also found that Csesalpinus and his contempo-
raries had been right in suspecting that the blood makes a
small circuit from the heart through the lungs and back
again. We will try to understand all this with the assistance
of a diagram, which, however, you must remember is only
to help you, and not a real drawing of the parts. Starting
from the left lower chamber a of the heart, the blood is
pumped out of the left top corner of this chamber into an
artery in the direction of the arrow i. This artery soon
divides into two branches, one going downwards by the
arrow 2 to the lower part of the body, the other upwards by
the arrow 2' to the arms and neck ; and, after flowing into
the different parts of the body, the blood in the lower arte?y

CH. XIV. DOUBLE CIRCULATION OF THE BLOOD. 113

Fig. 13.
NECK

LEFT

returns by the lower vein, while the blood of the upper
arte7'y is returning by the upper vein, and both streams pour
into the right upper chamber of
the heart, b.

The blood has now made one
round, but it does not stop here.
It escapes through some valves
down into the lower chamber c j
out of the right top corner of
which it starts again in the direc-
tion of arrows 8 and 9, and passes
through the lungs, returning by
the lung- veins, ox pulmonary veins
as they are called, in the direc-
tion of arrow 10, back into the
left top chamber of the heart, d.
From there it passes down into

the chamber a, from which it first « c. Lower chambers of the heart,

called ventricles, b d. Upper

Started, and the whole round be- chambers of the heart, called

auricles. The arrows and num-

ginS again. The first journey of bers show the course of the blood.

the blood round the whole body is called the general cir-
culation, and the second journey through the lungs is called
the pulmonajy circulation ; when Harvey had traced these
two journeys he had proved the double circulation of the
blood.

Although this discovery as stated here appears very
simple, yet it took Harvey nineteen years to trace the blood
through all the channels of the body, before he felt quite
certain that he had hit upon the truth. Meanwhile he had
returned to London, and had been made physician at St.
Bartholomew's Hospital. Here he taught his theory in his
Lectures of 16 19, and at last published a small book on the

Diagram of Heart and Blood-vessels
front.

I

114 SEVENTEENTH CENTURY. pt. hi.

circulation of the blood in 1628. Yet none of the older
physicians would believe he was right, and Harvey told a
friend that he lost many patients in consequence of his new
doctrine. It is greatly to the credit of the unfortunate King
Charles I., who was reigning at this time, and whose private
physician- rfarvey was, that he gave him many opportunities
of making physiological experiments on the animals in the
royal parks, and took great interest in his discoveries.
Harvey wrote several other valuable books, and traced the
development of the chicken in the ^gg. He was of a very
gentle and modest disposition, and disliked controversy so
much that he could scarcely be persuaded to publish his
later investigations when he found what disputes were occa-
sioned by his great discovery of the circulation of the
blood. He died in 1657, in his eightieth year.

Discovery of the Vessels which carry Nourishment to
the Blood, 1622-1649. — Harvey's doctrine of the circulation
of the blood was the real starting-point oi physiology^ or the
science of living bodies, and when the true action of the arte-
ries and veins was known, many other vessels of the body were
soon better understood. The most important of these were
the vessels which carr}^ nourishment from all parts of the body
to make fresh blood. In 1622 Gaspard Asellius, Professor
of Anatomy at Pavia, saw a white fluid flowing from some
thread-like tubes in the body of a dog which he was dis-
secting. This dog had been eating food just before he died,
and Asellius found that the fluid came from the intestines
and was the nourishing matter of the food. He called these
fine tubes lacteals, because the fluid in them looked
like milk. Some years later, in 1647, Jean Pecquet, an
anatomist of Dieppe, discovered that these lacteals empty
themselves into a large tube called the thoracic duct, which

CH. XIV. FURTHER PHYSIOLOGICAL DISCOVERIES. 115

carries the fluid into the principal vein, and so to the
heart j and finally, in 1649, ^ Swede named Olaiis Riidbeck
discovered an immense number of fine thread-like tubes
running firom all the principal parts of the body, and carrying
nourishing matter to the thoracic duct, and so through the
great vein to the heart. He called these tubes lymphatics;
but in reality the lymphatics and lacteals are the same
vessels, coming from different parts of the body and supplying
the material for new blood. You will easily understand that
when physiologists knew not only how the blood circulates
through the body, but also how a fresh supply of blood is
being constantly provided, they had made a great step
towards tracing out the working of a living body.

Chief Works consulted. — Sprengel, * Hist, de la Medecine,' 1815 ;
Harvey's 'Anatomical Exercises,' 1673; Aikin's * Biog. Mem. of
Medicine till the Time of Harvey,' 1780 ; Huxley's 'Elementary Phy-
siology ; ' Carpenter's ' Physiology ; ' Kirke's ' Physiology ; ' Cuvier,
'Hist, des Sciences, &c. ;' D'Orbigny, 'Diet, des Sciences.'

ii6 SEVENTEENTH CENTURY. pt. hi.

CHAPTER XV.

SCIENCE OF THE SEVENTEENTH CENTURY (CONTINUED).

Torricelli discovers the reason of Water rising in a Pump — Uses Mer-
cury to measure the Weight of the Atmosphere — Makes the First
Barometer — M. Perrier, at Pascal's suggestion, demonstrates varia-
tions in the pressure of the atmosphere — Otto Guericke invents the
Air-pump — Working of the Air-pump — Guericke proves the
Pressure of the Atmosphere by the experiment of the Magdeburg
Spheres — He makes the first Electrical Machine — Foundation of
Royal Society of London and other Academies of Science.

Torricelli's Invention of the Barometer, 1644. — We must
now turn to quite another subject on which new light was
being thrown at this time. Among the many different
mechanical experiments which GaHleo made during his Hfe,
there had been one with a common pump which puzzled
him very much, and which he had never been able to
explain.

You know that if you put the mouth of a squirt in water
and pull back the handle, the water rises up into the tube.
That is to say, as soon as you leave a space inside the squirt
quite empty without any air in it, the water rushes in.
In the same way, water may be made to rise up a long
tube standing with its open end in a pond or basin, by
drawing up a tight-fitting stopper a, Fig. 14, called a pis-
ton, and so driving the air out at the top and leaving
a vacuum inside the tube. But Galileo found that as
soon as the water had risen up to the height of about

CH. XV.

TORRICELLI—THE BAROMETER.

117

Fig. 14,

Ap
C

Z4-fiet

34 feet it would not mount any higher, even though the tube
between the surface of the water c, and the piston A, had no
air in it. He could not, how-
ever, find out why the water
should stop rising just at this
point, and it was not till after
his death that his friend and
follower Torricelli (born 1608),
who was a mathematical pro-
fessor at Florence, hit upon
the reason.

Torricelli asked himself,
' Why does the water rise in
the tube at all? something
must force it up.' Then it
occurred to him that air must
weigh something, and that it
might be this weight on the
open surface of the water
which forced the water up
the pump where there was no
air pressing it down. To un-
derstand this you must picture
to yourself all the air round our globe to be pressing down
upon the surface of the earth. Now, so long as the tube
also is full of air the surface of the water will all be equally
pressed down, and so will remain at one level at w b w.
But when the piston a is drawn up, it pushes the air above
it out of the tube, and so lifts the weight off the water at
B, which will immediately be forced up the tube by the
pressure of the air on the water outside from w to w. This

Section of a Suction-tube.

A, Tight-fitting piston, c, Greatest height
to which the water will rise. W B w.
Natural level of the water.

will go on till the water has risen about 34 feet to c and

ii8

SEVENTEENTH CENTURY.

PT. III.

Fig. 15.

then the column of water c b in the tube will press as heavily
on the water at b as the air does on the water outside from
w to w, so all the water w b w will again be equally pressed
upon, and no further rise will take place in the tube.

When Torricelli had made this discovery it occurred to
him that if it was really the weight of the air which sup-
ported the column of water it ought to lift mercury or

quicksilver, which is fourteen
times heavier, to one-four-
teenth of the height. So he
took some mercury, and filling
a tube A, about 34 inches long,
with it, he turned the tube
upside down into a basin of
mercury, which being open was
under the pressure of the at-
mosphere. The mercury began
at once to sink in the tube, and
finally settled down at b, about
30 inches above that in the
basin. From this Torricelli
knew that the weight of ordi-
nary air is sufficient to keep a
column of mercury at a height
of 30 inches in vacuum. He
had now therefore made an
instrument which would mea-
sure the weight of the air,
and as our atmosphere varies in weight according as the
weather is cold or hot, or damp or dry, a column of this
kind would be higher when the air was heavy and lower
when it was light. He kept this apparatus always in one

Torricelli's Experiment (Ganot).

CH. XV. THE THERMOMETER. 119

place, and observed that the mercury r3se above the 30
inches whenever the air was heavy, and sunk below when-
ever the air was light. When once this was discovered it
was easy to mark off inches and parts of inches on the side
of the tube so as to reckon how much the mercury rose and
fell each day.

This was the beginning of the barojneter, by which we
measure the weight of the atmosphere. It was a long time
before people would believe that anything so invisible as air
could affect the mercury, but this was at last clearly proved
by a man named M. Perrier, who carried a barometer
to the top of a mountain called the Puy de Dome, in
Auvergne. As the summit of a mountain reaches to a great
height in the atmosphere, it has, of course, less air resting
upon it than the valley below has, and so the mercury when
carried to this height not being pressed so much up the tube,
fell nearly 3 inches, and then rose again gradually as M.
Perrier came down into the valley below where there was a
greater weight of air. This experiment, which was suggested
by the famous French writer Pascal, proved beyond doubt that
it was the weight of the air which caused the mercury to rise.
If now, after reading this account, you go and look at an
ordinary upright barometer, you will perhaps be puzzled by
finding it all enclosed in wood, and you will ask how the
air can get to the mercury to press it down ; but if you look
carefully at the wooden box at the bottom, you will find a
small hole in the wood, often having a small plug of paper
in it to keep out the dust, and through this hole, even stuffed
up as it is, the pressure of the air can act. The space be-
tween the top of the column of mercury (b. Fig. 15) and the
end of the tube is a vacuum, or a space without any air in
it, and is still called a Torricellian vacuum.

I

I20 SEVENTEENTH CENTURY. pt. hi.

Invention of the Thermometer. — The date of the in-
vention of the thermometer (or instrument to measure heat)
is so uncertain that it will be best to speak of it here in con-
nection with the barometer. Galileo is said to have made
the first thermometer, which was simply a tube with a bulb
at the end standing upside down in a basin of water. The
bulb was filled with air, and when heat was applied to it, it
expanded and drove back the water in the tube. A few
years afterwards a Dutchman named Drebbel made thermo-
meters with spirits of wine in them, and finally, in 1670,
mercury was used. Mercurial thermometers have the bulb
and part of the tube filled with mercury, and the rest of
the tube is quite empty, all the air being driven out by
heating the mercury till it completely fills the tube, and
then melting the end so as to close it. When the mer-
cury cools it contracts and a vacuum is left above it. After-
wards, when the bulb of this thermometer is heated, the
mercury expands and rises in the tube j when it is chilled it
contracts and falls.

The thermometer was n'ot of any great use till early in
the eighteenth century, when three men, Fahrenheit, Celsius,
and Reaumur, measured off the tube into degrees, so that the
exact rise and fall could be known. Celsius and Reaumur
took the freezing-point of water as their lowest point ; but
Fahrenheit took the greatest cold he could obtain by a mix-
ture of snow and salt. For this reason 32° is the freezing
point of water in a Fahrenheit thermometer, and his other
divisions are different from those of Celsius or Reaumur.
Celsius's scale is now the one used all over the Continent,
and scientific men wished to introduce it into England, be-
cause it is so much more simple than Fahrenheit's. It is
called ' centigrade,' or a hundred steps, because the freezings

CH. XV.

GUERICKE—THE AIR-PUMP.

121

point of water is o°, and the tube is so divided that there are
exactly ioo° degrees between the freezing and the boiling
point.

Otto Guericke invents the Air-pump, 1650 The Tor-
ricellian vacuum in the barometer, was made, as we have
seen, by simply fiUing a glass tube more than 30 inches
long with mercury, and then turning it upside down into a
basin of the same, so that the mercury in the tube fell to 30
inches, and an empty space was left at the top. But in 1650,
a very few years after Torricelli's experiment, Otto Guericke,
a magistrate of Magdeburg, in Prussia, made another step
in advance and invented an au'-pump, by which air can be
drawn out of a vessel, leaving it almost empty. Fig, 16 is the

Fig. 16.

simplest kind of air-pump, and
the way it works is not difficult
to understand. At the bottom
is a glass jar which has a
round barrel or cylinder, b b,
fixed on the top of it. In the
cylinder is a tight-fitting piston,
c c, like the one in the suc-
tion-tube p. 117, only that this
one has in it a valve or door,
d. There is also another
valve, e, at the place where the
cylinder and glass jar meet,
and both these valves open

Air-pump (Knight),
upwards. Now suppose we i, «, Cylinder, .c. Piston with a valve.
start with both valves shut ^^,Valves opening upwards.

and the piston c c down at the bottom of the cyHnder rest-
ing on the valve, e. Then if we pull the piston gradually
up, the valve d will be kept shut by the air outside pressing

r

122 SEVENTEENTH CENTURY. pt. hi.

upon it, and so the piston will force the air between b and
B, out of the top of the cylinder. If the valve e remained
also shut there would now be a vacuum, or space without
air, in the cylinder b j but this will not be so, because
the air in the jar below, being no longer kept down by air
above it, will expand, and forcing up the valve e will fill the
whole of the jar and the cylinder with expanded air.

Now bring down the piston c c again and observe what
will happen. The thin air in the cylinder will be pressed
down upon the valve e and will shut it, and then, not being
able to get down into the jar, it will force up the valve d
again, and escape out at the top. The piston will now be
resting once more upon the valve e ; but the glass jar will
have much less air in it than it had at first, because it
will have lost all that which went up into the cylinder and
was pressed out at the top. You have only to repeat this
process and more air still will be drawn out, and thus by
moving the piston up and down you gradually empty the
glass jar. You cannot get quite all the air out, because
there must be enough left to push open the valve ^ when
you pull the piston up, but you can go on till there is
very little indeed. Air-pumps are now constructed, by which
the air can be entirely drawn out and a perfect vacuum
left ; but we are speaking of the one Guericke niade, which
was like the one I have described, only more complicated,
and he worked it under water to make quite sure that no
air should creep in at the cracks.

The Experiment of the Magdeburg Hemispheres. —
The first experiment which Guericke made with his air-
pump was to prove that the atmosphere round our earth is
pressing down upon us heavily and equally in all directions.
To do this he took two hollow metal hemispheres, like the

CH. XV. THE FIRST ELECTRICAL MACHINE, 12:

two halves of an orange with the inside taken out. These
hemispheres fitted tightly together, so that no air could pass
in or out when they were shut. Outside he fastened rings
to hold by, so as to pull them apart, and at the end of one
hemisphere he fixed a tap which fitted on to his air-pump.
Now, as long as there was air inside the closed globe the
two halves came apart quite easily ; but when he had drawn
out the air with the air-pump and turned off the tap so as to
leave a vacuum inside, it required immense strength to drag
the globe into two parts. This showed that the atmosphere
was pressing heavily on every side of the globe, forcing the
two halves firmly together, and as there was no air inside to
resist this pressure, the person trying to separate them had
to force back, as it were, the whole weight of the atmo-
sphere to get them apart. As Guericke was burgomaster of
Magdeburg, this experiment has always been called ' the ex-
periment of the Magdeburg hemispheres.'

The first Electrical Machine made by Guericke. —You
will remember that Gilbert had shown in 1600 that sulphur
and many other bodies, when they are rubbed, will attract
light substances. Since his time very little notice had been
taken of this fact, till Guericke invented the first rough elec-
trical machine in 1672. He made a globe of sulphur which
turned in a wooden frame, and by pressing a cloth against
it with his hand as it went round he caused the sulphur to
become charged with electricity. His apparatus was very
rough, but it led to better ones being made ; and some
years later, in 1740, a man named Hawksbee substituted a
glass globe for the sulphur and a piece of silk for the cloth,
and in this way electrical machines were made much like
those we now use.

Guericke also discovered that bodies charged with the

124 ■ SEVENTEENTH CENTURY, pt. hi.

same kind of electricity repel each other. If you hang a
piece of paper, or better still, a pith ball ^, upon a silk
thread b^ and hold near to it a piece of sealing-wax c rubbed
with dry flannel, you will find that the ball will at first be
attracted towards the seaHng-wax as in i, Fig. 17, but after a
few^ moments it will be repelled and will draw back as in 2 ;
nor mil it approach the sealing-wax again till it has been near
some other body, and given up part of the electricity it has
received. Thus an electrical body, as Guericke pointed out,

Pith-ball, attracted and repelled by rubbed sealing-wax.

attracts one that is not electrified, but repels it again as soon
as it has filled it with electricity like itself. He was also the
first to notice the spark of fire and crackling sound which
are produced by electricity when it passes between two
bodies which do not touch each other.

Foundation of the Royal Society of London and other
Academies of Science, 1645. — We must now return to Eng-
land, where about this time an event took place which,
though it seemed insignificant at the time, had in the end a
great influence upon science. In the year 1642 the unfor-
tunate King Charles I. began that civil war with his people
which ended in his being beheaded on January 30, 1649.
During these years all England was in a state of turmdil and
confusion, and in London especially the riots and disturb-

CH. XV. FOUNDATION OF THE ROYAL SOCIETY. 125

ances made it almost impossible for quiet and studious
people to live in peace. It was under these circumstances
that a small group of scientific men, among whom were
Robert Boyle, son of the Earl of Cork, and Dr. Hooke, an
eminent English mathematician, began to meet together
privately to try and forget public troubles in discussing
science. They assembled first in London in 1645, t»ut soon
moved to Oxford to be out of the way of the constant riots,
and continued to meet there till 1662, after the restoration
of Charles II., when they settled in London and formed
themselves into a regular Society under a charter from the
king.

This was the beginning of the Royal Society of London,
which has done so much for science during the last two hun-
dred years, and which is still the leading scientific society of
England. The following account of its early meetings is thus
given by Dr. Wallis, one of the first members, ' Our business,'
he says, 'was (precluding matters of theology and State
affairs) to discourse and consider of philosophical enquiries,
and such as related thereunto : as Physick, Anatomy,
Geometry, Astronomy, Navigation, Staticks, Magneticks,
Chymicks, Mechanicks, and Natural Experiments ; with the
state of these studies, and their cultivation at home and
abroad. We then discoursed of the circulation of the blood,
the valves in the veins, the venae lactae, the lymphatic vessels,
the Copemican hypothesis, the nature of comets and new
stars, the satellites of Jupiter, the oval shape (as it then
appeared) of Saturn, the spots on the sun and its turning on
its owTi axis, the inequalities and selenography of the moon,
the several phases of Venus and Mercury, the improvement
of telescopes and grinding of glasses for that purpose, the
weight of the air, the possibiHty or impossibility of vacuities

126 SEVENTEENTH CENTURY. pt. hi.

and Nature's abhorrence thereof, the Torricellian experiment
in quicksilver, the descent of heavy bodies and the degrees
of acceleration therein, with divers other things of like
nature, some of which were then but new discoveries, and
others not so generally known and embraced as they now
are ; with other things appertaining to what hath been
called the New Philosophy, which, from the times of Galileo
at Florence and Sir Francis Bacon (Lord Verulam) in
England, hath been much cultivated in Italy, France, Ger-
many, and other parts abroad, as well as with us in Eng-
land.'

How well we can picture from this account (written
in 1696), the pleasure which this little group of men,
weary of the quarrels and bloodshed of the times, felt in
discussing and investigating those laws of nature which seem
to bring us into the calm presence of an Almighty Un-
changing Power far above the petty wranglings of man !
The Royal Society has become, as I have said, one of the
grandest scientific bodies in the world ; but it has probably
never held more earnest or enthusiastic meetings than in the
small lodgings at Oxford where it first took its rise in the
midst of civil war.

England was not long the only country which had a
scientific society. Italy had already had two in the time of
Galileo and Torricelli, but they had soon been broken up
again. In Germany, the ' Imperial Academy of the Curious
in Nature' was founded in 1662; and in 1666 the famous
'French Academy of Sciences' was legally established by
the French Government in Paris.

All these societies were a great help in spreading the
knowledge of scientific discoveries. Men who before were
unable to publish what they knew, now sent or read their

CH. XV. EARL V MEMBERS OF THE RO YAL SOCIETY. 127

papers to those who could understand and appreciate them.
The Royal Society began from the first to publish useful
memoirs in their Philosophical Transactions ; and in 1669
we find them bringing out the works of an ItaHan anatomist,
Malpighi, of whom we shall speak presently, and who sent
to them works which he could not afford to publish in Italy.
By this means the information scattered about the world
was gathered together, and men were encouraged to seek
out new truths when there w^as a chance of their being
known and appreciated.

Among the earlier members of the Royal Society there
were some whose discoveries we must now consider. These
were Boyle and Hooke, whom we have already mentioned ;
John Mayow, whose experiments in chemistry are especially
interesting ; Ray, Grew, and Malpighi, naturalists and ana-
tomists ; the Dutch astronomer Huyghens ; the English
astronomer Halley, and last, but not least, England's great
philosopher, Sir Isaac Newton.

Chief Works consulted. — Ganot's 'Physics,' 1873; Balfour Stewart
on 'Heat,' 1871 ; Rossiter's 'Physics,' 1870 ; Baden Powell's 'Hist-
tory of Nat. Philosophy,' &c. ; Cuvier, * Histoire des Sciences,' &c. ;
Birch's * Hist, of Royal Society ;' Thomson's ' Hist, of Royal Society,'
1812.

128 SEVENTEENTH CENTURY. pt. hi.

CHAPTER XVI.

SCIENCE OF THE SEVENTEENTH CENTURY (CONTINUED).

Boyle's Law of the Compressibility of Gases — This same Law dis-
covered independently by Marriotte — Hooke's theory of Air being
the cause of Fire — Boyle's experiments with Animals under the
Air-pump — John Mayow, the greatest Chemist of the Seventeenth
Century — His experiments upon the Air used in Combustion —
Proves that the same portion is used in Respiration — Proves that
Air which has lost its Fire-air is Lighter — Mayow's ' Fire-air ' was
Oxygen, and his Lighter air Nitrogen — He traces out the effect
which Fire-air produces in Animals when Breathing.

Boyle's Law of the Compressibility of Gases, 1661. — The
Hon. Robert Boyle, seventh son of the Earl of Cork, and
one of the principal founders of the Royal Society, was bom
in 1626. He had very delicate health, and when quite
young travelled much abroad and learned there a great deal
about science even before he was eighteen years of age. He
was deeply interested in Galileo's discoveries, and was in
Florence when that great astronomer died in 1642.

After his return to England, when he was at Oxford, he
read an account of Guericke's air-pump, and was so de-
lighted with this new discovery that he set to work at once
to make one without ever having seen the original. He
succeeded so well, with the help of his friend and assistant
Dr. Hooke, that his air-pump became famous, and many
writers have by mistake given him the credit of being the

CH, XVI.

COMPRESSIBILITY OF GASES.

129

Fig. i8.

inventor. We have seen, however, that Guericke was the
first to hit upon this instrument ; Boyle only improved it,
and made with it many very valuable experiments upon the
weight and nature of air. These are too many and lengthy
for us to examine here ; but there is one law about the com-
pression of gases which you will find connected with Boyle's
name in all books on physics, and which you ought to under-
stand. Boyle knew from Torricelli's experiment that the
weight of the atmosphere upon the air, close down to our
earth is about equal to the weight of 30 inches of mercury in
a tube (see p. 118). Now he
wished to find out how much
air is compressed, or forced into
a smaller space, when more
weight is put upon it, and to
prove this he devised the fol-
lowing experiment. He took
a tube A*, open at the long
end and full of ordinary air,
and by putting a little mercury
into the tube and shaking it
carefully till it settled at the
bottom, he cut off a small quan-
tity of air between b and c.
This air was of course still un-
der the usual weight of the at-
mosphere, which pressed dowTi
upon the mercur}'^ through the
open end of the tube. But
the mercury did not add to »

the weight because it stood at the same height on both
sides of the tube, and so was evenly balanced.

Fressure

AtmospJiere
equals

1Z

-jQ

Pressure

of
Msrcury

-t30

25

-20

Its

--70

30

\--io

I30 SEVENTEENTH CEATUJRY. pt. III.

He next added more mercury, till it stood 30 inches higher
in the long end than in the short one (as seen in a*-*). The
air between b and c was now pressed down twice as much as
before, for it had the 30 inches of mercury weighing upon
it, as well as the atmosphere, which equalled another 30
inches. Boyle found that this double pressure had squeezed
it into half the space {b c, fig. a^) ; in other words, by
doubling the pressure he had halved the volume of the air.
He then poured in 30 inches more mercury, making the
pressure three times as great as at first, and he found the air
was now compressed into one-third of the space it had filled
at first. And this he proved to be the law of compression of
air and of all gases, that the volume of a gas (that is, the
space it fills) is decreased in proportion as the weight upon it is
increased. If you double the pressure you halve the
vohime j if you halve the pressure you double the volume.

This law of the compressibility of gases is known as
Boyle^s Law, or sometimes as Marriotte^s Law, because a
Frenchman named Marriotte also discovered it some years
later without knowing that Boyle had done so. It is not
always absolutely true, but we cannot stop to discuss the
exceptions here ; you will find them in books on physics and
chemistry.

Boyle and Hooke both gave much time to the study of
chemistry. Hooke published a theory in 1665 that air acts
upon substances when they are heated, and so produces fire ;
for, said he, in making charcoal, although the wood is in-
tensely heated and glows brightly, yet so long as the air is
kept away it will not be consumed. Boyle also proved that
a candle will not bum, nor animals breathe, without air.
He found that when he put mice and sparrows into his air-
pump, and then drew out the air, they died ; and that flies,

CH. XVI. JOHN MAYOW. 131

bees, and even worms, became insensible ; while fish,
though they lived longer than the mice, soon turned on their
backs and ceased to live. He also put a bird under a glass
vessel full of air, and it died after three-quarters of an hour.
It was clear, therefore, that fresh air is necessary to life, and
Boyle began to think that just as a candle-flame cannot be
kept up without air, so there must be some vital fire in the
heart which is extinguished when air is shut out from it.

This opinion he discussed at the Oxford meetings, and a
young physician named John JMayow listened very eagerly,
and then went home and set himself to try and find out what
this strange power in the air could be, without which neither
fire nor animals could exist.

Mayow's Experiments on Respiration and Combustion,
1645-1679. — John Mayow's private history is very short.
He was born in Cornwall in 1645 i ^^ became a Fellow of
All Souls', Oxford, and practised as a physician in Bath ; and
finally he died at the house of an apothecary in York Street,
Covent Garden, in 1679, before he was thirty-four years of
age. This is all we know about his life ; but he must have
been a diligent worker and a real lover of science, for though
he died so young he left behind him an account of a number
of experiments and discoveries which entitle him to be called
the greatest chemist of the seventeenth century. I wish we
could go through all his experiments, for they form a most
beautiful lesson of the earnest and painstaking way in which
God's laws should be investigated. Mayow never made a
careless experiment ; he never thrust in his own guesses
when it was possible, to work out the truth ; he went on
patiently step by step, taking every care to avoid mistakes,
and never resting till he had got to the bottom of his
difficulties. Let us now take some of his experiments on

132

SEVENTEENTH CENTURY.

PT. III.

combustio7tj or burning, and respiration, or breathing, and try
and follow them as carefully as he did.

It seemed to him clear from the experiments of Boyle
and Hooke that there must be something in the air which
gave rise to flame and breath, and that this could only be a
small part of the air, since a candle when put under a bell-
glass went out long before all the air was gone. He first of
all satisfied himself by experiments that this gas which
burnt, and which he called fire-air, was not only in the
atmosphere, but existed in nitre, or saltpetre, and also in
many acids ; and then he set to work to discover how much
of it there was in ordinary air. To do this he took a piece
of camphor, with some tinder dipped in melted sulphur,
and placed it on a little platform hung inside a bell-jar (see
Fig. 19). He then lowered the bell-jar into a basin of water,
having first put a siphon or bent tube under the bell-jar to
let enough air out for the water to rise. Then he took the
tube out, leaving the water at the same height inside and
outside the jar, while the rest of the jar above the water was

Fig. 19. Fig. 20.

Mayow's experiments on combustion and respiration (YeatsX

full of air. He now held up a burning-glass, and brought
the sun's rays to a focus upon the camphor and tinder till it
grew hot and burst into a flame. As it burnt he noticed that

CH. XVI. RESPIRATION AND COMBUSTION. 133

at first the water inside the jar sank down, because the air,
being heated, expanded and took up more room. Then after
a time the camphor ceased to burn, the jar cooled down, and
the water rose again higher than before, till it stood above the
water outside. The camphor was not all consumed, but
when he tried to light it again he could not succeed. Why
was this ? ' Because,' said Mayow, ' there are no fire-air
particles left in the jar to make the camphor burn, and the
using up of these particles has made the rest of the air shrink
and take up less space.'

He now wished to compare burning with breathing, so
he put a mouse in a cage and hung it inside the bell-jar,
which he arranged over the water as before. Little by little
as the mouse breathed the water crept up inside the jar, until
when it had risen to a certain height the mouse drooped and
died. It was clear, therefore, that animals in breathing use
up some portion of the air. But is it the same portion which
the flame uses ? Many people would have jumped at this
conclusion, but Mayow was not content till he had proved
it by another experiment. He put a lighted candle and a
mouse together inside the bell-jar. The water now rose
much faster than before ; the candle went out first, and then
the mouse drooped as soon as the water had risen to the
same height as in the other experiment. He was now
certain that the candle and mouse both used up the same
fire-air particles ; but to make still more sure, he put a candle
under a bell-jar where the air had been spoiled by breathing,
and it went out directly.

His next step was to try whether air was lighter or
heavier after the. fire-air had been used up. To do this he
put two mice into the jar, one at the top and the other at
the bottom j the one at the top drooped and died, while the

134 SEVENTEENTH CENTURY. PT. ill.

other was still breathing. This proved that the air which
had lost \\.'s> fire-air particles was lightest and "rose to the top,
so that the top mouse could no longer breathe. By these
and a great many other experiments Mayow proved that air
is made up of two portions — one heavy, which supports flame
and life ; the other light, and which is useless for burning or
breathing, and this last was the largest portion. I want you to
notice this particularly, because you will see by-and-by that
Mayow had really discovered and described two gases. The
one which he called yfr^-^/r was oxygen^ which was not known
to other chemists for more than one hundred years later, and
the other and lighter one is now called nitrogen.

Having now proved that an animal in breathing uses up
the same part of the air which a candle does in burning,
Mayow wanted next to know what this fire- air did inside the
animal. Harvey, as you remember, had proved that the
blood passes through the lungs and there meets the air which
we draw in at each breath. Here then, said Mayow, the
fire-air particles must come in contact with the blood, and,
joining with it in the same way as they do with the fat of
a candle, must cause the heat of the blood. If anyone wants
to prove this let him run fast. He will find that he is obliged
to breathe more quickly and draw more air into his lungs,
which will soon make his blood hotter and move more
quickly, till his whole body glows with warmth. But if this
mixture of the air with the blood does really take place, the
arteries into which blood has just flowed from the lungs and
heart ought to be full of air ; and this is easily proved to
be the case by putting warm arterial blood under an air-
pump, where, as soon as the pressure of the outside air is
taken off, innumerable bubbles rise out of the blood as fast
as they can come.

CH. XVI. BECHER AND STAHL—' PHLOGISTON: 135

In this way, by careful experiments and reasoning
Mayow succeeded in proving that fire-ah' (or oxygen) is
the chief agent in combustion and respiratmi. If he had
not died so young he might have become more known, and
men might have studied his discoveries, which he pubHshed
in 1674. Unfortunately, however, he did not live to spread
his knowledge, and a false theory of combustion caused his
work to be forgotten for many a long year.

Theory of * Phlogiston,' 1680-1723.— This mistaken
theory was proposed by two very eminent chemists, John
Joachim Becher (1625-1682) and Ernest Stahl (1660-
1734). Ernest Stahl in particular was a man of great
talent and perseverance, and he did a great deal for the
study of chemistry by collecting a great number of facts
about the way in which different substances combine to-
gether, and by arranging these facts into a system. But his
theory of combustion was quite mistaken, and it seems very
surprising that it should have been received by the chemists
of that day in the face of the facts so carefully proved by
Mayow. Stahl imagined that all bodies which would bum
contained an invisible substance which he called ^Phlo-
giston^ and that when a body was burnt it gave up its
phlogiston into the air, and could only regain it by taking it
out of the air or some other substance. It would only con-
fuse you to try and understand how this theory explained
some of the facts of chemistry. You will see at once one
which it did not explain, namely, why a body should grow
heavier when it is burnt, as Geber, 1,500 years before, had
shown it does. This fact alone ought to have been sufficient
to prevent the theory gaining ground ; but Stahl's fame was so
great, and his imaginary ' Phlogiston ' seemed to answer so
well in a gi*eat many problems, that chemists believed in it

136 SEVENTEENTH CENTURY. pt. hi.

for nearly a hundred years, and Mayow's true explanation
was forgotten till the eighteenth century, when fresh experi-
ments proved Stahl's theory to be false. ^

Chief Works consulted. — Brande's 'Manual of Chemistry' — Intro-
duction ; Rodwell's ' Birth of Chemistry ; ' Yeats ' On Claims of
INfodems to discoveries in Chemistry and Physiology,' 1798; Birch's
* Life of Boyle,' 1744 ; Shaw's ' Philosophical Works of Boyle,' 1725.

CH. XVII. FIRST USE OF THE MICROSCOPE. 137

CHAPTER XVII.

SCIENCE OF THE SEVENTEENTH CENTURY (CONTINUED).

Malpighi first uses the Microscope to examine Living Stractures — He
describes the Air-cells of the Lungs — Watches the Circulation of the
Blood —Observes the Malpighian layer in the human Skin — De-
scribes the structure of the Silkworm — Leeuwenhoeck discovers
Animalcules— Grew and Malpighi discover the Cellular Structure of
Plants — The Stomates in Leaves — They study the Germination of
Seeds — Ray and Willughby classify and describe Animals and Plants
— The Friendship of these two Men.

Use of the Microscope by Malpighi, 1661. — We have now
fairly left behind us the first fifty years of the seventeenth
century ; indeed, the experiments of Bo3de and Mayow were
all made after 1650. But I wish especially here to remind
you that we have just begun the second half of the century,
because it will help you to remember an important study
which began very quietly about this time, but which has in
the end opened out to us an entirely new world of discovery.
In the year 1609, at the beginning of the century, Galileo
brought distant worlds into view by the use of the telescope;
and in like manner in the year 1661, or about the middle of
the century, Malpighi, by the use oi ^^ microscope^ revealed
the wonders of infinitely minute structures, or parts of living
bodies ; enabling men to see fibres, vessels, and germs, which
were as much hidden before by their minuteness as the
moons of Jupiter had been by their distance. It is not quite
certain who invented the microscope (fUKpog, little ; aKOTriw, I
look) ; but as the first which were made were only telescopes

138 SEVENTEENTH CENTURY. pt. ni.

(see p. 97), with lenses of such a focus as to look at an object
near instead of far off, anyone may easily have hit upon the
idea. The important point was the use made of them, and
this, as far as regards the structure of living beings, we
owe to Malpighi.

Marcello Malpighi was born at Crevalcuore, near
Bologna, in the year 1628 ; he became Professor of Medi-
cine at the University of Bologna in 1656, and was early
distinguished for his discoveries in Anatomy, made chiefly
by the use of the microscope. It is not possible for us,
without a knowledge of anatomy, to understand thoroughly
the structures which he described, but we may be able to
form a general idea of the work he did.

One of his first experiments was the examination of the
general circulation of the blood in the stomach of a frog,
and he succeeded in demonstrating the fact that the arteries
are connected with the veins by means of minute tubes
called capillaries, thus proving beyond doubt the truth of
Harvey's doctrine. His next work was to study the passage
of the blood through the lungs (see p. 113), and to describe
the air-cells from which the blood derives its oxygen. If
you can get anyone to show you properly under the micro-
scope a section of a frog's lung, you will see a number of
round spaces bordered by a delicate partition ; these are
sections of air-cells, and round them you will see a network
of minute tubes. Through these tubes or capillaries the
blood flows in a living creature, and takes up oxygen from
the air through the coverings or membranes of the air-
cells and capillaries, giving back in exchange carbonic acid
to be breathed out into the atmosphere. Malpighi was the
first to point out these air-cells and to describe the way in
which the blood passes over them. After this he turned his

CH. XVII. IMPORTANT MICROSCOPIC DISCOVERIES. 139

attention to th-j tongue, and published in 1665 a careful de-
scription of all its nerves, vessels, and coverings. He also
pointed out that the outside layer of the skin or epidermis
of the negro is as white as yours or mine, and that the
colouring matter which gives him his dark colour is con-
tained in a deeper layer just at the point where the epidermis
joins the dermis or real fibrous skin beneath (see Fig 21.)
This soft layer is still called
the ' Malpighian layer,' and
the different colours of the
skins of animals are caused
by little cells of colouring
matter which lie buried in it.

After Malpighi had ex-
amined many other minute
structures of the human body,
he began next to study insects,
and in 1669 he published a
beautiful description of the silkworm.

Section of the Skin (Huxley).

a, Epidermis, b, Its deeper layer, or
Malpighian layer, c, Upper part of
the dermis, or true skin, d d, Per-
spiration ducts.

With his microscope
he discovered the small holes or pores which are to be seen
along both sides of the body of insects, and he found that
these pores were openings into minute air-tubes, which pass
into every part of the insect's body, and form a breathing
apparatus. He also described the peculiar vessels in which
the silkworm secretes the juice from which its silk is made,
and he traced the changes which the different parts of the
worm undergo as it turns into the moth. In fact, he was
the first man who attempted to trace out the anatomy of
such small creatures as insects ; a study to which men now
often devote their whole lives.

But grand as Malpighi's discoveries were, a Dutchman
named Leeuwenhceck (born 1632, died 1723) made the micro-

I40 SEVENTEENTH CENTURY. pt. hi.

scope tell even a more wonderful tale, for he detected in
water and in the insides of animals those extremely minute
beings which he called animalcules. He showed that a
piece of the soft roe of the cod-fish not bigger than an ordi-
nary grain of sand might contain ten thousand oi these living
creatures. When such tiny beings as these could be seen
and examined, I think you will acknowledge that I did not
speak too strongly when I said that the microscope has
opened out to us a new and marvellous world of life.

Vegetable Anatomy, Grew and MalpigM, 1670. —
From insects IMalpighi next turned to plants j and it is
curious that at about the same time an English botanist
named Nehemiah Grew (born 1628, died 171 1), who was se-
cretary to the Royal Society, also took up the same study ;
and the papers of the two men were laid before the Royal
Society on the same day in 1670. Malpighi's complete
work was afterwards published in 1674, and Grew's in 1682.
The investigations of these two men agreed in many re-
markable points ; they had both of them examined with
great care the flesh (if we may call it so) of plants, and they
described for the first time the tiny bags or cells of which
every part of a plant is made, and which you may easily see
for yourself if you put a very thin piece
of the pulpy part of an apple, or better
still, of the pith of elder under the
microscope (see Fig. 22). They had
also noticed the long tubes which He
among the woody fibres in the stringy
or fibrous part of a plant and in the
Cellular tissue from the vcins of the Icavcs, and Grew had

pith of the elder (Oliver). ^

pointed out quite truly that these
tubes, which are called vessels or ducts^ are composed of

cii. XVII. VEGETABLE ANATOMY. 141

Strings of cells which have grown together into one long cell
or tube.

Grew also first saw those beautifiil little months in the
skin of the leaves called stomates, which open when the air
is damp, and serve for taking in and giving out air and
moisture. To see these you must take a very thin piece of
the skin of the under part of a leaf, and place it in water
under the microscope ; you will see a number of very small
roundish or oval spaces {a, Fig. 23), and if you watch care-
fully you will most likely see some of fig. 23.
them open in the water. Grew dis- a-
covered these stomates and pointed out rCt^s^
their use. He also studied very care- D-ViVa?'''^
fully the way in which seeds begin to v-V^feJs
sprout ; but on this point Malpighi did Vn^Ciy
the most, for he watched under the ^<-v'
microscope the whole process of the ^^^^^ken w ?h?unde!--
growth of seeds, and described all the f^ liZtTX CeUs
different states of the germ, comparing "^ '^^ '^^" (Carpenter).
them to the growth of a chicken in the Qgg, and showing
how much an egg and a seed resemble each other in many
particulars.

By these few examples you can form an idea how much
Grew and Malpighi did towards the study of the structure
of plants or Vegetable Anatomy, a science which they may
almost be said to have founded, and one which you may
work at yourself with the help of a fairly good microscope
and an elementary book on Botany. If you will do this
with patience and care you will be well repaid; for some of
the most beautiful and delicate of the contrivances of Nature
lie hid in those frail flowers which we gather for their
scent and beauty, and fling away without imagining what

142 SEVENTEENTH CENTURY. pt. hi.

wonderful structures they can reveal to us even when dead
and withered.

Classification of Plants and Animals by Eay and
Willughby, 1693-1705. — We now come to the history of
two friends, which is in itself a pleasure to dwell upon,
even if they had not both been great men ; but which be-
comes much more interesting when we remember that it was
their love of the study of Nature which first brought them
together, and which made them inseparable, not only in life,
but in their works after death.

John Ray, one of the greatest botanists of the seven-
teenth century, was born near Braintree, in Essex, in the
year 1628. Though only the son of a blacksmith, he re-
ceived a good education at the grammar school of the town,
and went afterwards to Cambridge, where he remained as a
tutor after he had taken his degree. Here one of his first
pupils was a Mr. Francis Willughby, of Middleton Hall, in
Warwickshire, a man seven years younger than himself, and
belonging to quite a different rank in society. These two
men, however, had one great interest in common — they were
both passionately fond of Natural History, and spent all their
spare time in studying it together.

They soon found that the descriptions and classifications
of plants and animals which had been drawn up by earlier
naturalists were very imperfect, and they formed the project
of drawing up a complete classification of all known plants
and animals, describing them as far as they were able, and
arranging them in groups according to their different cha-
racters. Willughby undertook the birds, beasts, and fishes,
while Ray devoted himself chiefly to plants; but they worked
together in all the branches, and Ray, as we shall see, ended
by doing far more than his share of the work.

CH. XVII. ZOOLOGY. 143

From 1663 to 1666 the two friends travelled together
over England, France, Germany, and Italy, making col-
lections of animals and plants, and Willughby took a pleasure
in using his wealth to add to the knowledge of his poorer
companion. Soon after their return Ray was made a fellow
of the Royal Society, and Willughby was not long before he
received the same honour. Willughby now married, and
though Ray continued his travels alone, yet a great part of
his time was spent at Middleton Hall, where the two friends
made experiments upon sap in the trees and the way it
flows.

In this way they worked together till, in 1672, Mr.
Willughby died of a fever, leaving a sum of sixty pounds a
year to Ray, and begging him to bring up his two little sons
and to continue his works on Zoology, which he had left un-
finished. The way in which Ray fulfilled these requests fully
showed the affection which he felt for his lost friend. He
brought up the boys till they were removed from his care by
relations ; and as to the works, he edited them with so much
care and such a touching desire to give every credit to
Willughby, that much of the work which must have been
Ray's stands in his friend's name, and in fame, as in life, it
is impossible to separate them.

I can only give you a very general idea of the kind of
classifications which Ray and Willughby adopted, for a mere
list of classes would be neither interesting nor useful to you.
The first book, which was on Quadrtipeds, was published by
Ray in 1693. He divided these first, as Aristotle had done,
into oviparous, or those that are born from eggs, like frogs
and lizards ; and viviparous, or those which are bom alive,
like lambs and kittens. He then divided the viviparous
quadrupeds into those which have the hoof all in one piece,

144 SEVENTEENTH CENTURY. pt. III.

like the horse, and those with a spHt hoof, Hke the ox and
goat. Those with spUt hoofs he divided again according as
they chewed the cud, Hke the ox, or did not, Hke the pig.
Then came the animals whose hoofs are split into many parts,
as the hippopotamus and rhinoceros ; then those which have
nails only in place of toes, as the elephant ; then those which
have toes but no separation between the fourth and fifth toes,
as the cat, dog, and mole ; and lastly, those which havei the
fifth finger, or toe, quite separate, as the monkeys. After
this he divided them more fully, by their teeth, and thus
made a very fair classification of quadrupeds.

The book upon Birds, which comes next in order, had
already been published by Ray in 1677, four years after
Willughby's death. In it birds were divided first into land-
birds and water-birds, and then were classified by the shape
of their beak and claws, and according as they fed upon flesh
like the vulture, or upon fruit and seeds like the parrot. The
water-birds were also divided into those which were long-
legged, as the flamingo, or short-legged, as the duck, and
according as the web between their toes was more or less
complete.

The ' History of Fishes ' is given as the joint work of Ray
and Willughby ; the groups into which they divided them
are nearly the same as those now used, but they are too
diflicult to explain here.

The ^ History of Insects ' was Ray's work, and was pub-
lished by friends after his death, in the same way as he had
published Willughby's. He divided insects into — first, those
which undergo metamorphosis (that is, turn from the cater-
pillar into the moth), as the silkworm, and all moths and but-
terflies ; and second, those which do not change their form ;
and then he sub-divided them according to the number of
their feet, the shape of their wings, and many other characters.

CH. XVII. J^AVS CLASSIFICATION OF PLANTS. 145

But Ray's greatest work was upon Plants, which he
classified much more perfectly than Csesalpinus had done.
He divided them first into imperfect plants^ or those whose
flowers are invisible, as mosses and mushrooms ; and pei-fect
plants^ or those having visible flowers. The perfect plants
he divided into two classes — first, the dicotyledons., or those
whose seeds open out into two seed-leaves, like the wall-
flower or the bean, in which last you can see the two cotyle-
dons very clearly if you take off" the outer skin ; and secondly,
the monocotyledons, or those whose seeds have only 07ie large
seed-leaf, like a grain of wheat. The dicotyledons he again
divided into those having simple flowers, like the buttercup,
and those whose flowers are compound., like the daisy j for if
you pick a daisy to pieces you will find that the centre is
made up of a number of little flowers, each of them perfect
in itself. It will have its own green calyx and coloured
corolla, and its o^vn stamens and seed-vessel ; therefore each
daisy is a branch of little flowerets, or a compound ?iow&[:.
Ray went on next to class the simple flowers according to
the number of seeds they bore, and the way in which the
seeds were arranged in the seed-vessel. In this way he
made a rough but complete classification of all the known
plants. Linnsus, the great botanist of the eighteenth
century, adopted many of Ray's divisions, which had mean-
while been made more perfect by Joseph Toumefort, a
Frenchman, bom at Aix, in Provence, in 1656.

Ray outlived his friend Willughby more than thirty
years, and died in 1705 at the age of seventy-seven. His
death brings us to the end of the Natural History of the seven-
teenth century, so far as we have been able to notice it. But
I cannot too often remind you that these four men, Malpighi,
Grew, Ray, and Willughby, are merely a few among an
8

146 SEVENTEENTH CENTURY. pt. hi.

immense number of observers in the same line of study. I
have picked out those whose work you could best under-
stand, and whose names ought to be known to you ; but I
could have selected not four but forty others who ought to
have been mentioned, if my book and your knowledge had
been greater. We must be content to catch here and there a
glimpse of the advance that was being made, always remem-
bering that an almost inexhaustible store of further infor-
mation remains behind when we have opportunity to seek
for it.

Chief Works consulted. — Cuvier, 'Hist, des Sciences Naturelles ; '
Carpenter's ' Physiology ; ' Sprengel, ' Histoire de la Medecine ; '
Whewell's ' History of Inductive Sciences ; ' Carpenter, ' On the Micro-
scope ; ' ' Memorial of John Ray,' E. Lankester, 1846 ; * Life of Ray
and Willughby,' Naturalists' Library, vol. xxxv. ; Lardner's * Encyclo-
paedia '—Classification of Animals.

cii. XVIII. SIR ISAAC NEWTON. 147

CHAPTER XVIII.

SCIENCE OF THE SEVENTEENTH CENTURY (CONTINUED).

1642, Birth of Newton — His Education — 1666, His three great Dis-
coveries first occur to him — Method of Fluxions and Differential
Calculus — First thought of the Theory of Gravitation — Failure of
his Results in consequence of the Faulty Measurement of the size of
the Earth — 1682, Hears of Picart's new Measurement — Works out
the result correctly, and proves the Theory of Gravitation — Ex-
planation of this Theory — Establishes the Law that Attraction
varies inversely as the squares of the distance — 1687, Publishes the
' Principia ' — Some of the Problems dealt with in this Work.

Newton, 1642. — We must now leave the living creation to
return to physical science, for, during all those years with
which we have been occupied since the time of Galileo
and Kepler, a boy had been growing up into rcanhood, who
was to become one of the greatest men of science that Eng-
land has ever known. In 1642, the same year in which
Galileo died, a child was bom at Woolsthorpe, near Gran-
tham in Lincolnshire, who was so tiny that his mother said
^ she could put him into a quart mug.' This tiny delicate
baby was to become the great philosopher Newton.

We hear of him that he was at first very idle and inattentive
at school, but, having been one day passed in the class by
one of his schoolfellows, he determined to regain his place,
and soon succeeded in rising to the head of them all. In
his play hours, when the other boys were romping, he
amused himself by making little mechanical toys, such as a

148 SEVENTEENTH CENTURY. pt. hi.

water clock, a mill, turned by a mouse, a carriage moved
by the person who sat in it, and many other ingenious contri-
vances. When he was fifteen his mother sent for him home
to manage the farm which belonged to their estate \ but it
was soon clear that he was of no use as a farmer, for though
he tried hard to do his work, his mind was not in it, and he
was only happy when he could settle down under a hedge
with his book to study some difficult problem. At last one
of his uncles, seeing how bent the boy was upon study, per-
suaded his mother to send him back to school and to
college, where he soon passed all his companions in mathe-
matics, and became a Fellow of Trinity College, Cambridge,
in 1667. But even before this, in the year 1666, his busy
mind had already begun to work out the three greatest dis-
coveries of his life. In that year he invented the remarkable
mathematical process called the ^ Method of Fluxions^ \f\i\Qh
is almost the same as that now called the 'Differential
Calculus,' invented about the same time by Leibnitz, a great
German mathematician. In that year he also made the dis-
coveries about Light and Colour ^ which we shall speak of
by-and-by ; and again in that year he first thought out the
great Theory of Gravitation^ which we must now consider.

Theory of Gravitation, 1666. — In the course of his
astronomical studies, Newton had come across a problem
which he could not solve. The problem was this. Why
does the moon always move round the earth, and the planets
round the su;i? The natural thing is for a body to go
straight on. If you roll a marble along the floor it moves
on in a straight line, and if it were not stopped by the air
and the floor, it would roll on for ever. Why, then, should the
bodies in the sky go round and round, and not straight fo7"ward 1

While Newton was still pondering over this question, the

CH. xvni. NEWTON S STUDIES. 149

plague broke out in Cambridge in the year 1665, and he was
forced to go back to Woolsthorpe. Here he was sitting one
day in the garden, meditating as usual, when an apple from
the tree before him snapped from its stalk and fell to the
ground. This attracted Newton's attention ; he asked
himself, Why does the apple fall ? and the answer he found
was, Because the earth pulls it. This was not quite a new
thought, for many clever men before Newton had imagined
that things were held down to the earth by a kind of force,
but they had never made any use of the idea. Newton, on
the contrary, seized upon it at once, and began to reason
farther. If the earth pulls the apple, said he, and not only
the apple but things very high up in the air, why should it
not pull the moon, and so keep it going round and round
the earth instead of moving on in a straight line ? And if
the earth pulls the moon, may not the sun in the same way
pull the earth and the planets, and so keep them going
round and round with the sun as their centre, just as if they
were all held to it by invisible strings ?

You can understand this idea of Newton's by taking a
ball with a piece of string fastened to it, and swinging it
round. If you were to let the string go, the ball would fly
off in a straight line, but as long as you hold it, it will go
round and round you. Thus Newton imagined that every-
thing near the earth is pulled towards it by an invisible force,
as you would pull the ball by the string \ but the ball does
not come to you, although the string pulls it, because of the
other force which is carrying it onwards j and in the same,
way the moon would not come to the earth, but would go on
revolving round it.

Newton felt convinced that this guess was right, and that
\kiQ force of gravitation, as he called it, kept the moon going

I50 SEVENTEENTH CENTURY. ft. hi.

round the earth, and the planets round the sun. But a mere
guess is not enough in science, so he set to work to prove by
very difficult calculations what the effect ought to be if it was
true that the earth pulled or attracted the moon. To make
these calculations it was necessary to know exactly the
distance from the centre of the earth to its surface, because
the attraction would have to be reckoned as strongest at the
centre of the earth, and then as gradually decreasing till it
reached the moon. Now the size of the earth was not accu-
rately known, so Newton had to use the best measurement
he could get, and to his great disappointment his calcula-
tions came out wrong. The moon in fact moved more
slowly than it ought to do according to his theory. The
difference was small, for the pull of the earth was only one-
sixth greater than it should have been : but Newton was too
cautious to neglect this error. He still believed his theory
to be true, but he had no right to assume that it was, unless
he could work it out correctly. So he put away his papers
in a drawer and waited till he should find some way out of
the difficulty.

This is one of many examples of the patience men must
have who wish to make really great discoveries. Newton
waited sixteen years before he solved the problem, or spoke
to anyone of the great thought in his mind. But more
light came at last ; it was in 1666, when he was only twenty-
four, that he saw the apple fall ; and it was in 1682 that he
heard one day at the Royal Society that a Frenchman
named Picart had measured the size of the earth very accu-
rately, and had found that it was larger than had been sup-
posed. Newton saw at once that this would alter all his
calculations. Directly he heard it he went home, took
out his papers, and set to work again with the new figures.

en. XVIII. THE LAW OF GRAVITATION. 151

Imagine his satisfaction when it came out perfectly right !
It is said that he was so agitated when he saw that it was
going to succeed, that he was obHged to ask a friend to
finish working out the calculation for him. His patience was
rewarded \ the attraction of the earth exactly agreed with the
rate of movement of the moon, and he knew now that he
had discovered the law which governed the motions of the
heavenly bodies.

This law of Newton's is called the * Law of Gravttatmi,^
and we must now try to understand what it is. Gravitation
means the drawing of one thing towards another, or towards
a centre. All the objects upon our earth are held there by
gravity, which pulls or attracts them towards the centre of
the earth. If there were no such thing as gravity there would
be nothing to prevent our chairs and tables, and even our-
selves, from flying into space ; but they are all held to the
earth by gravity, and if you dig a hole under them they
fall directly nearer to the centre.

Now let us see how this attraction of gravitation affects
the planets. Every one of the bodies in the heavens pulls or
attracts all the other bodies, just in the same way as the earth
attracts the apple on the tree. But as they are all moving
rapidly along (like the ball swung round your head) they do
not fall into each other, but the smaller bodies move round
the larger ones which are near them, just as if they were
fastened to them by invisible elastic threads. The smaller
ones move round the larger one, because it is not only
each body as a whole which pulls the other bodies, but
every tiny atom of matter in each planet is pulling at all
the atoms in all the other planets; so that the bigger a
body is, and the more atoms it has in it, the more it will
draw other bodies towards it. Our sun pulls the planets,

152

SEVENTEENTH CENTURY.

PT. III.

and the planets pull the sun ; but our sun has 700 times
more atoms in it than all the planets put together, and so it
keeps them moving round it. In the same way our earth
has eighty times more atoms in it than our moon, and so it
keeps the moon moving round it.

In this way the force of gravity keeps all the different
planets in their paths or orbits. It does not set them moving ;
some other force unknown to us first started them across the
sky — gravitation is only the force which determines the direc-
tion in which they move.

It was a grand thing to have discovered this force, but it
would have been of little value to Astronomy to know that
the heavenly bodies attracted each other unless it could also
be known how much influence they have upon each other.
This also Newton worked out accurately. You will remem-
ber that Kepler had shown that planets move in ellipses,
having the sun in one of the two foci (see fig. 10, p. 99).
Knowing this, Newton was able to calculate how much the
sun attracts a planet when it is near, and how much when it
is far off, so as to make it move in an ellipse j and he found

that exactly as much as the
square of the distance increases,
so much the attraction de-
creases ; that is, the attraction
grows less and less at a regular
rate as you go farther away
from the body that is pulling.
For instance, suppose that
at the point i, fig. 24, a planet
was one million of miles away
from the sun, and was being
When it arrived at the point

attracted with immense force.

CH. XVIII. THE ' FRINCIPIA:

153

3 it would be about twice as far, or two millions of miles
distant ; and the square of 2 being 4 (2 x 2 = 4), the at-
traction of the sun at this point will be only one-fourth as
much as it was at the point i. At the point 7 the planet
would be about three times as far, or three millions of miles
from the sun, and as the square of 3 is 9 (3 x 3 = 9), the
attraction here will be only ith of the attraction at the point
I. And so the calculation goes on ; if the planet went 12
millions of miles off, the attraction would be y^^ what it was
at first, and at 92 milHons of miles the attraction would be
¥T6"¥ 5 so that when the planet is very far away the attraction
becomes very slight indeed, but it will never entirely cease.
In scientific language this law is expressed by the words,
The attractioit vai'ies inversely as the square of the distance.
When once this law was known, it explained in a most
beautiful and complete way not only the three laws of Kep-
ler, but all the complex movements of the heavenly bodies.
These Newton worked out with the greatest accuracy by
the help of his ' Method of Fluxions,' which enabled him
to calculate all the varying rates at which the planets move
in consequence of their mutual attraction ; and he showed
that whenever we know clearly the position and mass of all
the bodies attracting a planet, the law of gravitation exactly
accounts for the direction in which it moves.

If you will consider for a moment what a labour it must-
be to calculate how much all the different planets pull each
other at different times — when they are near together and
when they are far off, when they are near each other and
near th sun, or near each other and far from the sun, in
fact in all the different positions you can imagine — you may
form some idea of the tremendous work he did. When he
published his great book, the ' Principia,' in 1687, there were

154 SEVENTEENTH CENTURY. pt. III.

iiot more than eight people in the world who were able to
understand the full meaning of his calculations and reason-
ings; and though his theory of gravitation was well received,
and his name became one of the most renowned and
honoured in the world, yet it was more than fifty years
before his work was thoroughly appreciated.

It may therefore easily be imagined that it is not possible
to give a simple sketch of what is contained in the ' Prin-
cipia ; ' but some idea may perhaps be formed of the
grandeur of the law of gravitation from an enumeration of
some of the problems which Newton explained by its action.

1. He explained those laws of motion which Galileo had
proved by experiment, and showed that it is the force of
gravity which causes the weight of bodies ; and determines,
when combined with other laws, the rate at which they fall,
and the path they describe.

2. He worked out the specific gravity of the planets,
showing, for example, that the matter of which Saturn is
composed is about nine times lighter than the matter of our
earth.

3. He showed how the attractions of the sun and of the
moon cause the tides of the sea, and worked out accurately
the reason of the spring and neap tides.

4. He proved that the earth could not be a perfect globe,
and measured almost exactly how great the bulge at the
equator and the flattening at the poles must be. And this
he did entirely by calculation, for no measurements had then
been made, to lead anyone to doubt that the earth was a
perfect globe.

5. He gave a complete explanation of the cause of the
* precession of the equinoxes,' the occurrence of which, as
you will remember, Hipparchus had discovered (see p. 30).

CH. XVIII. LAW OF GRAVITATfON EXPLAINED. 155

6. He not only showed why the planets move in ellipses
while a line joining the sun and a planet cuts off equal areas
in equal times; but he also accounted for many irregularities
in these movements, arising from their mutual attractions,
thus showing that gravitation exj)lains not only the general
laws but even apparent exceptions.

7. Of all bodies comets are apparently the most irregu-
lar, yet Newton calculated that they probably move in a
peculiar curve called a parabola, and since his time it has
been proved that the motions of all comets can be suffi-
ciently well explained by this theory, with the exception of
a few which move in ordinary ellipses like the planets, and
return periodically. These and many other problems of
the universe Newton showed could all be referred to the
action of gravitation ; and he concluded his work with a
grand description of the mechanism of the heavens, dwelling
with deep reverence upon the thought of that Infinite Mind
which gave rise to such a wonderful and complex machinery,
working in perfect order.

Chief Works consulted. — Brewster's 'Life of Newton;' ' Lives of
Eminent Persons ' — Lib. of Useful Knowledge ; Airy's ' Elementary
Astronomy ; ' Airy, ' On Gravitation.'

156 SEVENTEENTH CENTURY. I'x. in.

CHAPTER XIX.

SCIENCE OF THE SEVENTEENTH CENTURY (CONTINUED).

Transits of Mercuiy and Venus — Kepler foretells their occurrence —
1 63 1, Gassendi observes a Transit of Mercury — 1639, Horrocks
foretells and observes a Transit of Venus — 1676, Halley sees a
Transit of Mercury, and it suggests to him a method for Measuring
the Distance of the Sun — 1691-1716, Halley describes this method
to the Royal Society — Explanation of Halley's method.

First transits ever observed of Mercury and Venus, 1631-
1639. — We must now pause for a moment before passing on
to Newton's discoveries in Optics, in order to mention a re-
markable astronomical suggestion made about this time by
the astronomer Halley (born 1656, died 1742), who was the
friend and disciple of Newton.

You cannot fail to have heard and read something about
the expeditions sent last Decemberj 1874, into all parts of
the world to observe the Transit (or Passage) of Venus
across the sun. The object of these observations was to
measure the sun's distance from the earth j and Halley was
the first to propose this method of measurement, in 1691,
and to show how it might be accomplished.

You know that the two planets Mercury and Venus are
nearer to the sun than our earth is, and are therefore con-
stantly passing between us and it. But usually they pass
either below or above the sun, and it is only rarely that
they cross over the bright disc, so as to be seen through

CH. XIX. THE TRANSIT OF VENUS FIRST SEEN. 157

the telescope as a round black spot upon the sun's face.
With Mercury this happens at intervals of from seven to
thirteen years \ but with Venus it is much more rare, for
though two transits generally come together with an in-
terval of only eight years between them, yet after this there
is a gap of more than a hundred years before another
transit occurs.

After Kepler had finished the famous Rudolphine Tables
he was able to use them to calculate when these transits
would take place ; and he showed that both Mercury and
Venus would cross the sun's disc on certain days in the
year 1631. A French philosopher named Gassendi took
advantage of this prediction, and managed to observe Mer-
cury passing across the face of the sun on November 7, 163 1.
He was the first who ever observed a transit. With Venus
he was not so fortunate, for the transit of that planet took
place when it was night at Paris, and so Gassendi had no
chance of observing it.

It was not long, however, before this too was seen.
You will remember that two transits of Venus occur close
together with only eight years between them. Now Kepler
had imagined that in 1639 Venus would pass a little to the
south of the sun, and so no transit would take place. A
young Englishman, however, named Jeremiah Horrocks,
only twenty years of age, after going carefully over Kepler's
tables, felt convinced that there would be a transit, and he
even calculated within a few minutes the time when Venus
would enter upon the sun's face. Full of enthusiasm at the
chance of seeing this grand sight, he wrote to a friend at a
distance, begging him also to watch through the telescope at
three o'clock on the afternoon of December 4, 1639. His
expectations were not disappointed, for at fifteen minutes

158 SEVENTEENTH CENTURY. pt. hi.

past three on that day the planet began to creep over the
face of the sun. For twenty minutes Horrocks watched it,
and then the sun set and he could see no more. He had
been able to notice, however, that Venus was much smaller
in comparison with the sun than had been formerly supposed.
Horrocks and his friend Crabtree were the only people in
the whole world who saw this transit of Venus, the first one
ever observed.

Halley suggests that the Sun's distance may be
measured by the Transit of Venus, 1691. — This was all
that was known about transits when Halley went to St.
Helena in 1676 to study the stars of the southern hemi-
sphere. Here he also observed a transit of Mercury, and
after watching the small black spot travelling across the
face of the sun, and noting the time it took in going from
one side to the other, the idea occurred to him that it
would be possible to learn the distance of the sun by mea-
suring the path of a planet across its face. As Mercury,
however, is very fa,r from us, and near to the sun, it would
not answer the purpose so well as Venus, which is much
nearer the earth.

Halley knew that another transit of Venus would take
place in 1761, and as he could not hope to live till then, he
read a paper to the Royal Society in 1691, and another in
1 7 16, beseeching the astronomers who should live after him
not to let such an opportunity pass, and describing the way
in which the observations should be made. It is this
method which we must now try to understand as far as it is
possible without mathematics.

First of all I must tell you two facts which astronomers
knew already. The proportion of the distances of the
planets was ascertained, as you will remember, by Kepler
(see p. roo). Therefore it was known that Venus is (^w. round

CH. XIX. H ALLEY'S METHOD. 159

numbers) 2\ times as far from the sim as she is from the
earth. It was also known by the apparent size of the sun
that the sufis distance is about 108 times his diameter., or, in
other words, if you could measure the number of miles
across the face of the sun and multiply that number by
108, it would give you the sun's distance from the earth.
Therefore you see the one point to be learnt was. How
many miles wide is the face of the sun ?

Now suppose you place a globe or any other object upon
the table in the middle of the room, as at G, Fig. 25, and place
yourself at the point a.
The globe will then hide
from you (or eclipse) the
point c on the opposite
wall. Move your posi-
tion to B, and the globe
will then hide the point
D. If the globe is (as
at g) exactly half-way ^. ^ -^ , , ,■" t. , „ .^..

' ■' ■' Diagram showing how the distance between the

between VOU and the points p c and d c can be known, without

•' measuring them.

wall t"hf» two nnintS D g, A globe half-way between d c and a b. ^, A

and c will be the same

distance apart as the points a and b. But if you move the
globe to g, which is three tim.es as far from the opposite wall
as it is from you, then the points d and c will also be three
times as far apart as the points a and b. So that by know-
ing how much farther the globe is from the wall than it is
from you, you can tell accurately the distance between the
points hidden without measuring them.

It is exactly in this way that Halley proposed to measure
off a certain number of miles upon the face of the sun. We
are able to learn accurately how many miles distant any two
places are upon our globe. Suppose, therefore, that two

i6o SEVENTEENTH CENTURY. ft. in.

men go to places 7,200 miles apart, and each observes Venus
at a particular moment upon the sun's face. Just as you,
from two different positions, saw the globe cover two

Fig. 26.

Venus as seen upon the sun by two observers, one at e' and one at E. (Proctor.)

s. The sun. V v', Appearance of Venus on the sun's face. Venus Is travelling- in the
direction of the arrow.

different points of the wall, so these men will see Venus
against different points in the sun, as in Fig. 26 \ and since the
distance between Venus and the sun is 2 J times her distance
from the earth, the two points will be 2 J times 7,200 miles,
that is 18,000 miles apart. Here, then, we have a certain
number of miles measured off on the sun's face. But how
are we to tell accurately what proportion this interval be-
tween the spots bears to the whole diameter of the sun ?

By Halley's method the whole time that Venus takes in
crossing the sun is used as the means of measurement.
The observer at each of the two stations notes exactly the
time when Venus begins to cross the face of the sun, and
the moment when she passes off it again, and so reckons
exactly how long she has taken in making the whole transit.

It was already known, from the rate at which Venus
moves, exactly how long she would take in crossing the
centre or widest part of the sun. We will call this time 6
hours, so as to use whole numbers. But it is clear that in
crossing a narrower part of the disc she will take less time.
Suppose, therefore, that one man says she was exactly 5

CH. XIX. THE SUN'S DIAMETER. i6i

hours crossing from a to b, Fig. 27, and the other that she
was 5j hours crossing from c to d. This will give us the
measurement necessary to lay p^^

down the position of the two
transits on paper.

Draw a circle any size
you please, and, ruling a line
across the centre, divide it
into six parts (as in Fig. 27^),
to represent the 6 hours which
Venus would take in crossing
the centre ; each of those parts
will then represent the dis- Transit of Venus.

tance which she travels in an s, Face of the sun. v, Venus. a b,

Transit observed so as to occupy five
hour : 5x of these, tlierefore, hours, c d. Same transit observed so

as to occupy five-and-a-quarter hours.

will be the distance she travels

in 5:^ hours. Take this length in your compasses, and
place it at any part of the circle where it will meet the edge
at both ends, and in that position draw the line c d. Then
take a second length of five parts only, and placing it below
the other, rule the line a b parallel to c d. These two
lines express the path of Venus, as observed by the two
men, and we already know that the distance between them
is 2 J times 7,200, or 18,000 miles.

It is now easy to compare this interval with the sun's
diameter. Suppose for instance that 47 such- spaces will
cover the whole diameter of the circle, as they would if the
lines were drawn accurately in the observed positions, then
18,000 X 47, or 846,000 miles, would be the measure of the
sun's diameter. Now, we saw (p 159) that the sun's dis-

* It must be drawn very much larger to approach to anything like
accuracy. This figure merely indicates the method.

iG2 SEVENTEENTH CENTURY. pt. hi.

tance is io8 times his diameter ; therefore 846,000 x 108,
or 91,368,000 miles would, by these measurements, be the
distance of the sun from the earth; and this is as near as we
can arrive at the truth when taking whole numbers.

You will perhaps ask, if the measurement of the transit is
such a simple process, why it takes months to make the
proper calculations. But you must remember that in our
description we have neglected all the difficulties which really
occur. Our earth is not standing still as we have supposed
it to be. It is not only moving along in its orbit, but it is
turning round on its axis all the time, and this has to be
very carefully considered in choosing stations for observing
the transit, and allowed for in the results. Then, since our
earth moves in an ellipse, we are not always at the same
distance from the sun ; this also has to be allowed for.
Such simple difficulties as these you can understand, but
there are a great number of others which make the calcula-
tions very complicated indeed. Therefore you must not
imagine that you know all about the transit of Venus when
you have read this description of Halley's method. If you
have some general idea of the way by which the sun's
distance is found out, you will have learnt more than many
people ; and you must wait till you have studied mathe-
matics before you can expect to have a thorough knowledge
of the matter.

You will- be glad to hear that Halley's advice was not
neglected. Several transit expeditions were sent out in 1761,
and again in 1769, when the celebrated Captain Cook made a
voyage to the Pacific Ocean for this purpose and ; it is to
correct these observations that no less than forty-six expe-
ditions were sent out last year from Europe and America.
Halley made many other valuable astronomical observa-

CH. XIX. H ALLEY'S COMET. 163

tions.' He was the first astronomer who foretold the return
of a comet. Before his time it was thought that they went
away and never came back again ; but when the comet of
1682 appeared, Halley began to search for former records
of comets and found that one had been seen about every
seventy-six years, reckoning backwards from 1682. There-
fore he thought these must all be the same comet, and he
foretold its return in 1758. It came as predicted, and has
ever since been called ' Halley 's comet' Halley died in
1742, and with him ends the astronomy of the seventeenth
century.

Chief Works consulted. — Proctor's ' Transits of Venus j ' Herschel's

* Astronomy ; ' Denison's * Astronomy without Mathematics ; ' Airy's

* Popular Astronomy.'

1 64 SEVENTEENTH CENTURY, rr. iii.

CHAPTER XX.

SCIENCE OF THE SEVENTEENTH CENTURY (CONTINUED).

Newton's Discovery of the Dispersion of Light — Traces the amount
of Refraction of each of the Coloured Rays — Makes a Rotating
Disc turning the colours of the Spectrum into white Light
— Reason why all Light passing through glass is not Coloured —
Mr. Chester More Hall discovers the Difference of Dispersive Power
in Flint and Crown Glass — Newton's Papers destroyed by his pet
dog — Last years of Newton's life.

Newton publishes his Discovery of the Dispersion of
Light, 1671. — We must now return to Newton, and consider
his third great discovery, which was about Hght. You will
remember that he had to wait sixteen years between his first
attempt to investigate the law of gravitation, and that new
measurement of the earth which enabled him to prove the
truth of his theory. During this time he had by no means
been idle. He once said that the reason he had succeeded
in making discoveries was that he gave all his attention to
one subject at a time ; from 1666 to 1671, when his papers
on gravitation were quite laid aside, the subject to which he
devoted himself was Light.

In the early part of the seventeenth century several
people had tried to find out what it was that gave rise to
different colours. An Italian archbishop named Antonio
de Dominis (died 1625) had given a better explanation of
the rainbow than Roger Bacon had given before him ; and

ClI. XX.

THE DISPERSION OF LIGHT.

165

Fig. 28.

Descartes had gone farther, and had pointed out that a ray
of light seen through a clear, angular, polished piece of glass,
called a prism (see Fig. 28), is spread
out into colours exactly like the rain-
bow ; but no one had yet been able
to say what was the cause of these dif-
ferent tints. Newton was the first to
work this out in his usual accurate and painstaking way.
He tells us that in 1666 he 'procured a triangular glass
prism, to try therewith the celebrated phenomena of
colours,' and in the very first experiment he was struck by a
very curious fact. He had made a round hole f (Fig. 29),

Glass Prism.

Fig. 29.

Newton's first Experiment on Dispersion of Light.

D E, Window shutter, f, Round hole in it. ABC, Glass prism. M N, Wall on
which the spectrum was thrown.

about one-third of an inch broad, in the window-shutter,
D E, of a dark room, and placed close to it a glass prism,
A B c, so as to refract the sun-light upwards towards the
opposite wall of the room, m n, making the line of colours
(red, orange, yellow, green, blue, indigo, and violet), which
Descartes had pointed out, and which Newton called a
spectrum^ from specto, I behold.

While he was watching and admiring the beautiful
colours, the thought struck him that it was curious the
spectrum should be long instead of round. The rays of

1

1 66 SEVENTEENTH CENTURY. pt. hi.

light come from the sun, which is round, therefore, if they
were all bent or refracted equally, there ought to be a
round spot upon the wall ; instead of which it was long
with rounded ends, like a sun drawn out lengthways. What
could be the reason of the rays falling into this long shape ?
At first he thought that it might be because some of them
passed through a thinner part of the prism, and so were less
refracted ; but when he tested this by sending one ray through
a thin part of the prism, and another through a thick part,
he found that they were both equally spread out into a
spectrum. Then he thought that there might be some flaw
in the glass, and he took another prism ; still, however, the
spectrum remained long, as before. Next he considered
whether the different angles at which the rays of the sun fell
upon the prism had anything to do with it, but after calcu-
lating this mathematically he found the difference was too
small to have any effect. Finally, he tried whether it was
possible that the rays had been bent into curves in passing
through the prism, but he found by measurement that this
again was not the reason.

At last, after carefully proving that none of these expla-.
nations was the true one, he began to suspect that it mus-
be something peculiar in the different coloured rays them-
selves, which caused them to divide one from the other.
To prove this he made the following experiment : — He made
a hole, F, in the shutter, as before, and passed the light
through the prism, a b c, throwing the spectrum upon a
screen, m n. He then pierced a tiny hole through the screen
at the point g, Fig. 30 ; the hole in this board was so small
that the rays of only one colour could pass through at a
time. Newton first let a red ray pass through, so that it v/as
bent by the prism, h i k, and made a shaded red spot on

CH. XX. NEWTON— DISPERSION OF LIGHT.

167

the wall at R \ here he put a mark. He now moved the first
prism, A B c, a little, so as to let the second, or orange ray,
pass through the hole g. This xsiy fell upn exactly the same
spot of the second prism, h i k, as the red ray had done, but
it did not go to the same spot on the wall ; it was more bent in
passing through the prism, and made an orange spot at o.

Fig. 30.

Diagram showing the Different Refraction of Rays of Different Colours.

D E, Shutter. F, Round hole, a b c. First prism. M N, Screen receiving the
spectrum, g. Small hole through which the rays of only one colour can pass.
H I K, Second prism refracting those rays.

above the point r. By this Newton knew that an orange
ray is more refracted in passing through a prism than a red
ray is. He moved his prism, a b c, again, so as to let the
yellow ray through. ^ This was still more bent, and fell above
o on the point y. In this way he let all the different
coloured rays pass through the hole, marking the points on
which they fell, and he found that each ray was more bent
than the last one, till he had marked out a second complete
spectrum on the wall. Only the two extreme rays, red and
violet, are traced out in Fig. 30, to avoid confusion.

This experiment proved clearly, ist, that light is made icp of
differently coloured rays ; and 2nd, that these rays are differently
refracted in passing through a prism. The red rays are least
bent, and the violet ones most, while each of the other rays

1 68

SEVENTEENTH CENTURY.

PT. III.

between these have their own course through the prism. I
must warn you, however, not to think that there are exactly
seven colours : there are really an infinite number, passing
gradually into each other j Newton only divided them
roughly into seven for convenience.

This spreading out of the different coloured rays is called
the dispersion of light. I wish I could give you the many
beautiful experiments which Newton made to prove it, but
I have only room for one, which you can easily try for
yourself, by which the different colours which make up
the spectrum can be turned back again into white light.
You will see at once that if it is true that white light can
be divided up into colours, those same colours when re-
united must make white. To show this Newton took a
round card and painted upon it the seven colours, as pure as
possible, five times over, like a spectrum five times repeated
(a, Fig. 31), and then spun it round rapidly, so that the eye
received the impression of all the seven colours at once
(b, Fig. 31). If you do this you will see the card looks a

Fig. ^i.

A, Newton's disc. B, Disc rotating.

dirty white, because the colours blend together just as they
do in a ray of light. You will not get a pure white, because

CH. XX. THE ACHROMATIC TELESCOPE, 169

the artificial colours are not pure, and also because it is
difficult to paint each colour in the proper proportion.

But now that we have proved that light is broken up
into colours in passing through a denser medium, you may
perhaps ask how it is that we do not see coloured rays when-
ever we look at the sun through glass or any other trans-
parent substance. The reason is that when the two sides of
the glass are parallel (that is, lie always at the same distance
from each other), the ray of light is bent just as much in
going out from the glass into the air as it was when it came
in from the air into the glass, and so it remains just as it was
at first. When the two sides are not parallel, as in a rounded
lens, colours do appear in the thin edges of the glass, and
these used to be very troublesome in telescopes and micro-
scopes. Newton . thought that they could never be" got rid
of, for he did not know that light is spread out or dispersed
more in one kind of glass than in another. But two years
after his death, in 1729, Mr. Chester More Hall, of Essex,
found that two kinds of glass (flint-glass and crown-glass)
disperse light differently, so that when you put them together
they correct each other, and the coloured rays at the edges
are blended into white light. Telescopes and microscopes
which are made in this way are called achroinatic (from a,
without ; chroma^ colour). A patent for such instruments was
taken out by a Mr. Dollond in 1757, and he probably in-
vented them without having heard of Mr. Hall's discover}'-.

It would require a whole volume to give you all Newton's
investigations into the nature of light, and his experiments
on the coloured rings of the soap-bubble and other trans-
parent substances. His work on Optics was read before the
Royal Society in 167 1 and 1672, but the ideas were so new
that many clever men, who should have known better,

9

lyo SEVENTEENTH CENTURY. pt. hi.

attacked him with a number of foohsh and ignorant ob-
jections, till at last he told his friend Huyghens that he was
almost sorry he had ever made them public.

After his great work, the ' Principia,' had been published
in 1687, he next turned his attention to chemistiy, but un-
fortunately all the results of his labour in this science were
destroyed by an accident. One day when he was in chapel,
his pet dog Diamond turned over a lighted taper, which set
fire to all the papers on which his work was written. When
he returned and found the charred heap it is said that he
merely exclaimed, * Oh Diamond, Diamond ! thou little
thinkest the mischief thou hast done ! ' but his grief at the
loss of his work affected his brain, and though he re-
covered and lived another forty years, publishing many
editions of his works, yet he never made any more great
discoveries.

Newton received many honouiG in his old age : in 1699
he was elected Master of the Mint, and a member of the
French Royal Academy of Sciences ; in 1703 he was made
President of the Royal Society, and in 1705 he was knighted
by Queen Anne. Like all truly great men, he was modest
as to his own abilities, and always willing to be taught by
others. He felt so strongly how much we have still to
learn about the Universe, that he considered his own dis-
coveries as very trifling indeed. A short time before his
death he said of himself, * I know not what the world may
think of my labours ; but to myself I seem to have been only
like a boy playing on the sea-shore, and diverting myself in
now and then finding a smoother pebble or a prettier shell
than ordinary, whilst the great ocean of truth lay all un-
discovered before me.' Yet this man who spoke so humbly
was the discoverer of the greatest and most universal lav/

CH. XX. DEATH OF NEWTON. 171

known to mankind ! He loved to seek out new laws, but he
was more anxious to collect facts and to make sure that he
was right, than eager to publish his conclusions. It was the
truth he loved, and not the fame which it brought. His
patience and perseverance were unbounded ; he was never
in a hurry, but turned a subject over and over in his mind,
for years together, seizing upon every new light shed upon
it, and waiting patiently for more. And through all his
labours he looked reverently up to the One Great Light
whose guiding power he loved to trace and to acknowledge
in all the wonders of the universe. He died in 1727 at
eighty-five years of age, and was buried in Westminster
Abbey, his pall being borne by the first nobles of the land.

Chief Works consulted. — Newton's 'Optics,' 1721 j Ganot's
'Physics;' Rossiter's 'Physics;' Brewster's 'Encyclopaedia,' art.
* Optics ; ' Herschel's * Familiar Lectures.*

172 SEVENTEENTH CENTURY. pt. hi.

CHAPTER XXI.

SCIENCE OF THE SEVENTEENTH CENTURY (CONTINUED).

Roemer measures the Velocity of Light— Newton's Corpuscular Theory
of Light — Undulatory or Wave-theory proposed by Huyghens —
Invention of Cycloidal Pendulums by Huyghens — Discovery of
Saturn's Ring — Sound caused by Vibration of Air — Light by Vibra-
tion of Ether — Reasons why we see Light — Reflection of "Waves of
Light — Cause of Colour — Refraction explained by the Undulatory
Theory — Mr. Tylor's Illustration of Refraction — Double Refraction
explained by Huyghens -Polarisation of Light not understood till
the nineteenth century.

Olaus Eoemer measures the Velocity of Light, 1676.—

While Newton was dispersing light in prisms, and finding
out its nature, Olaus Roemer, a famous Danish astronomer
(born 1644, died 17 10), was engaged in something almost
as wonderful. He was measuring the rate at which light
travels across the sky ! It seems at first as if this would
be impossible, but we now know three different ways of
accomplishing it ; Roemer's was the first attempt ever
made, and his measurement was very near indeed to the
truth.

You will remember that Jupiter has four moons, which
move round it as our moon moves round our earth. Three
of these moons are so near Jupiter and move round it in
such a manner that they pass through its shadow and are
eclipsed every time they go round. Now it became very

cii. XXI. VELOCITY OF LIGHT. 173

useful, for certain astronomical reasons, to know exactly when
these eclipses happened, and the time of their occurrence
was therefore calculated very carefully ev^ since Galileo
first discovered them. There was no difficulty in doing this,
and yet, strange to say, the eclipses rarely happened exactly
at the right moment. Sometimes they were too early, some-
times too late, and they varied according to some regular
rule as much as 16 minutes 36 seconds on each side of the
exact moment when they ought to have happened.

At last it occurred to Roemer, and to an Italian astrono-
mer named Cassini, that, as Jupiter is farther away from the
earth at one time than at another, the eclipses might be seen
some minutes later whenever the rays of light from the
moons had to cross a greater distance to reach the earth.
Cassini seems to have put the thought aside and not to have
worked it out ; but Roemer seized upon it, and by careful
calculations proved that it was the tme answer to the diffi-
culty. If the earth was at e (Fig. 32) for example, when Jupiter

Fig. 32.

Diflferent Distances at which Jupiter's Light reaches the Earth.
J, Jupiter. E e'. The earth.

was at J, the light would not have nearly so far to travel as if
the earth was at e' ; and in this last position the 16 minutes
36 seconds would be taken up by the light crossing the
earth's orbit from e to e'. This distance was known to be
about 190,000,000 miles, so that light travels at the rate

174 SEVENTEENTH CENTURY. pt. hi.

of 190,000,000 miles in 996 seconds, or about 190,000
miles in a second. This is seven million times as fast as the
quickest express train.

Huyghens and Newton — Theories of Light. — The time
had now come when so much was known about the way in
which light behaves, that philosophers began to ask them-
selves, ' What is Light?' — a question by no means so easily
answered as you may think ; for though it is by means of
light that we see everything, yet light in itself is invisible.
You will exclaim at once that you can see a sunbeam
shining through a crack in a window- shutter. But what you
see is not light itself, it is the particles of dust or smoke
which are acted upon by light so that they shine. There is
one very simple way of proving to yourself that rays of light
are not visible lines. When the moon is shining you know
that it is reflecting the light of the sun, therefore there must
be light crossing the sky and falling upon its surface. But
now look up some other night when the moon is not there.
All is darkness ; yet the light must be there just the same,
and would have caused the moon to shine if it had been
there also, but as there is nothing to reflect it to your eye it
is invisible.

What, then, is this light, invisible in itself, yet without
which we can see nothing? Newton thought that it was
composed of minute invisible particles of matter which
darted out in straight lines from luminous or light-giving
bodies, and falling upon our eyes caused the sensation which
we call light. This is called the Corpuscular^ or sometimes
the Emission, Theory of Light. It was very ingenious, and
accounted for a great many of the facts, but there were
many others which it did not explain ; and I will not
attempt to describe it to you, because another theory, called

CH. XXI. VARIOUS THEORIES OF IIGHT. 175

the Undulatory {or Wave) Theory of Lights has now been
found to be much more complete and satisfactory. This
last theory was first proposed by a Dutch mathematician
and astronomer named Christian Huyghens, the son of
Constantine Huyghens, Counsellor to the Prince of Orange.

Christian Huyghens was born at the Hague, in Holland,
in the year 1629 ; when he was only thirteen years old he
was already passionately fond of mathematics, and ex-
amined every piece of machinery that fell in his way. He
received a very good education, and wrote some able treatises
upon geometry when he was only two-and- twenty. From
this time he advanced very rapidly, both writing valuable
papers and making grand discoveries. In 1658 he invented
a peculiar kind of pendulum called the cycloidal pendulum,
which would keep accurate time when swinging over wide
spaces ', and he was also the first to apply pendulums to
clocks. In 1659 he made a telescope ten feet long, with
which he discovered one of Saturn's satellites, and described
accurately Saturn's ring, which Galileo had mistaken for two
stars. In 1660 he came to England, and solved some
questions which the Royal Society had proposed about
the laws of motion. Then he was invited to settle in France,
and it was there, in 1678, that he read before the ' Academie
des Sciences ' the theory of light which we must now try to
understand.

Undulatory Theory of Light, 1678.— I must first tell
you that Newton, among his many other investigations, had
shown that sound is caused by a trembling or vibration of
the air. Thus, when you strike the wire of a harp, the
trembling of the string shakes the air, and the quivering
motion travels along like waves upon a pond, until some
wave strikes the drum of your ear and produces the sen-

176 SEVENTEENTH CENTURY. pt. iit.

sation we call sound. The tighter and shorter the string, is,
the more rapid the vibrations or waves will be, and the
more shrill will be the note which you hear.

Now Huyghens said, ' We can only explain light by sup-
posing it to be a vibi-ation like sound.' But here at the
very outset came a difficulty. We know that light is not a
vibration of the air, for if you draw the air completely out of
a glass vessel, light will still pass across it; and besides, we g^t
light from the sun and the distant stars, so that it has to
come across a great airless space before it reaches the at-
mosphere of our earth. And yet, if light is a vibration, it is
clear there must be something between the sun and us to
vibrate. To meet this difficulty Huyghens supposed the
whole of space between our earth and the most distant stars to
be filled with an elastic invisible suhsta7tce which he called
^ ether. ^ He assumed this substance to be so fine and
subtle that it passes between the atoms, even of solid
objects, and that the sun and all luminous bodies cause it
to vibrate so that its undulations or waves strike upon our
eyes and give rise to the sensation we call light.

Thus, according to this theory, when you look at the
sun, the invisible ' ether ' filling the whole space between you
and it, is moving up and down in rapid vibrations, just as if
the sun held one end of a cloth and you the other, and the
sun was shaking the cloth so that the waves travelled along
it to your eye ; and every wave that hit you would cause
the sensation called light.

This theory explains very well how light-waves may be
in the sky and yet we may not see them ; for if a stick
is moving rapidly to and fro in the air, and you go within
reach of it you feel pain, but if you keep out of reach no
pain is produced. In the same way, when the vibration of

CH. XXI. THE UNDULATORY THEORY. 177

this invisible ether strikes your eye you feel light, but
though the waves may be travelling rapidly across the sky.
so long as they do not fall upon your eye, no light will be
produced to you.

But suppose you were not looking at the sun, but at the
ground, why should you still see ? Because the waves from
the sun which strike the ground cannot travel on so easily
through the solid earth as through the pure ether, so a great
number of them bound off and vibrate back along the ether
again, from the ground to your eye ; and as they vibrate dif-
ferently according as the ground is rough or smooth,, hard or
soft, wet or dry, they make a different impression upon your
eye, and cause you to see a picture of the ground as it is.

Clear white glass and other perfectly transparent bodies
let nearly all the waves of light pass through them and send
hardly any back to your eye ; and people have in conse-
quence been known to walk right up against glass doors with-
out seeing them. Bright polished surfaces, on the contrary,
like steel and mercury, turn nearly all the waves back again,
and this is why we see our own faces reflected so clearly in
a looking-glass, where it is the mercury at the back which is
the real mirror.

If we had room we might follow out these light-vibrations
in a very interesting manner. For instance, why does a
leaf look green and a soldier's coat red? Because, as in
sound the kind of note you hear depends upon the quick-
ness of the vibrations of the air, so in light it depends upon
the quickness of the vibrations of the ether what colour you
see. The vibrations which produce violet, indigo, blue,
green, yellow, orange, and red, have travelled all together as
white light through the ether, but they are differently treated
by the leaf All except the green waves are quenched, or

178 SEVENTEENTH CENTURY. pt. in.

absorbed 2JS> it is called, by the material of the leaf, and only
the green waves bound back upon your eye. In other words,
the vibrations of the ether coming from the leaf move exactly
fast enough to produce upon your eye the sensation you call
green^ just as the vibration of the air caused by a particular
string of a harp produces on your ear the sensation of the
note you call the middle C.

Refraction of Light explained by Hnyghens. — But we
must now go back to Huyghens, and point out how beauti-
fully he explained by his undulatory theoiy the refraction or
bending-back of rays of which we have already spoken so
much. When a wave of light is travelling onwards, he said,
if it passes vertically into glass or any denser substance, the
wave will move more slowly, but it will still go straight on,
because both ends of th :^ wave will be equally checked. But
if the wave goes into the glass obliquely (see p. 47), one end
of it will reach the glass first before the other, and will move
slowly, while the other end goes on unchecked, and so the
wave will swing round and will have its direction altered.
In the same way, when it passes out again from the glass,
one end will pass out first, and will move more easily in the
air than the end that is still in the glass, and so it will swing
round again and make another bend.

You must not be disappointed if you do not understand
this at once, for it is very difficult \ to make it easier we will
borrow a very ingenious illustration given last year (Jan. i,
1874) by Mr. E. B. Tylor, in a periodical called 'Nature.'
Take two small wheels about 2 inches round, and mount
them loosely upon a stout iron axle measuring about half-an-
inch round. This will make a runner like two wheels of a
cart, and if you let it roll down a smooth board it will repre-
sent very fairly the crests or tops of the waves of light in

CH. XXI. DOUBLE REFRACTION OF LIGHT.

179

Fig. 33.

the ether. Let your board be about 2 J feet long, and at one
end of it glue on pieces of thick-piled velvet of the shape
of lenses (see i, 2, 3, Fig. zz\ Let your runner first
go straight down the board
upon the velvet; it will then
run through the velvet with-
out changing its course, as a
vertical ray does through a
lens. Then start it obliquely
across the board so that it will
reach the lens i in the position
B. Here the left wheel of the
runner will touch the velvet
first, and will be checked by
the rough pile, while the right
wheel moves on quickly as be-
fore, and thus the runner will
swing round or be refracted
towards the thick part of the
lens. Then, as it passes out
again the right wheel will come
out of the velvet first and will
move more quickly on the

-::%''"

Figures illustrating the passage of the
waves of light through difFerent-
shaped lenses (Tylor).

smooth board, while the left is still checked by the velvet at
c ; therefore the runner will again be shifted round or re-
fj-aded as it passes out. You can easily foUoAV the course
of the runner through the other lenses for yourself,. always
noticing that the arrow marks which way the ray of light is
coming; and when you have done this you will have a
beautiful imitation of the way in which the waves of light
are refracted in passing through different mediums.

Double Refraction. — There is still one more remarkable

i8o SEVENTEENTH CENTURY. ft. hi.

fact about light which Huyghens explained; namely, the
double refraction of light through a crystal called Iceland spar.
A physician of Copenhagen named Erasmus Bartholinus had
received from Iceland a crystal in the form of a rhomboid
(see Fig. 34), which, when broken, fell into pieces of the
same shape. Bartholinus called this

Fig. 34. ^

. 7 crystal ' Iceland spar,' and while mak-

Z® / ing experiments with it he observed

/ that an inkspot or any small object

A spot of ink seen through a seen through it appeared to be doubled.

crystal of Iceland spar. °

He was not able to explain this curious
fact, but he published an account of it in 1669, and Huy-
ghens accounted for it quite correctly by suggesting that the
crystal was more elastic in one direction than in the other,
so that a wave of light passing into it was divided into two
waves moving at differeat rates through the crystals. This
would cause them to be bent differently— one according to
Snell's ordinary law of refraction (see p. 107), and the other
in an extraordinary way. Thus these two separate rays fall-
ing upon the eye would cause there the impression of two
objects.

This curious effect is very interesting to study, and it led
Huyghens to make a number of remarkable experiments.
He found that the two rays when they passed out at the
other side of the crystal remained quite separate the one from
the other, and if they were afterwards sent through another
crystal in the same direction that they had gone through the
first, they went on each their own way. But now came a very
extraordinary fact : if the second crystal was turned round
a little so that the rays passed in rather a different direction
through it, each ray was again split up into two, so that there
w^ere now four rays, sometimes all equally bright, sometimes

cir. XXI, POLARIZATION OF LIGHT. 18 1

of unequal brightness, but the light of all four was never
greater than the light of the one ray, out of which they had
all come. These four rays continued apart while he turned
the second crystal more and more round ; till, when he had
turned it 90°, or a quarter of a circle, the rays became two
again, with this remarkable peculiarity, that they had changed
characters ! The ray which before had been refracted in
the ordinary way now took the extraordinary direction, while
the other chose the ordinary one.

This curious effect observed by Huyghens is now known
as the ^ ;polai'ization of light ' by crystals. It is very difficult
to understand, and you must be content at present to know
that he discovered the fact. There is a beautiful explanation
of it, but we must wait for that till we consider the science
of the nineteenth century, for it is now much better under-
stood. Huyghens' * Theory of Light ' was published in 1690,
under the title ' Traite de la Lumiere.' He remained in
Paris for some years -, but left it and returned to Holland
when the persecution of the Protestants began after the
revocation of the Edict of Nantes. He died in 1695.

Chief Works consulted. — Ilerschel's ' Familiar Lectures ' — art.
'Light;' Tylor, < On Refraction'— * Nature,' vol. ix. ; * Edin. Phil.
Journal,' vols. ii. and iii. — 'On Double Refraction;' Ganot's 'Phy-
sics ;' Encyclopjedias— ' Britannica,' ' Metropolitana,' and Brewster's.

1 82 SEVENTEENTH CENTURY. ft. hi.

CHAPTER XXIL

SUMMARY OF THE SCIENCE OF THE SEVENTEENTH
CENTURY.

We have now arrived at the close of the seventeenth century,
and it only remains for us, before going farther, to try and
picture to ourselves the great steps in advance which had
been made between the years 1600 and 1700. We saw at
p. 82 that the work of the sixteenth century consisted
chiefly in making men aware of their own ignorance, and
teaching them to inquire into the facts of nature, instead of
merely repeating what they had heard from others. In the
seventeenth century we find them following out this rule of
patient research, and being rewarded by arriving at grand
and true laws.

Astronomy. — To begin with Astronomy. Here Galileo
led the way with his telescope. The structure of the moon,
with its mountains and valleys ; the existence of Jupiter's
four moons revolving round it and giving it light by night ;
the myriads of stars of the Milky Way j the spots of the sun
coming into view at regular intervals, and thus proving that
the sun turns on its axis ; all these discoveries forced upon
men's minds the truth that our little world is not the centre
of everything, but a mere speck among the millions of
heavenly bodies. But while they humbled man's false pride
in his own importance, they taught him on the other hand
the true greatness which God has put in his power by giving

CH. XXII. SUMMARY. 1S3

the intellect to discover and understand these wonderful
truths if he will only seek them in an earnest and teachable
spirit.

Then came Kepler with a still grander lesson, for he
showed that the movements of the planets are governed by
regular and fixed laws, which can be traced out so accurately
that an astronomer is able to foretell with confidence what
will happen many years after he himself has passed away.
Thus we see Gassendi and Horrocks, by the use of Kepler's
labours, calculating within a few minutes the time of a
planet's passage across the face of the sun and watching the
exact fulfilment of the prediction. Nor is this all : so exact
and true are these movements, and so completely is man
able to read them rightly, that by this simple passage of a
small black spot across the sun Halley showed that we may
actually number the millions of miles between ourselves and
the great light around which we move. We might almost
think that we had now travelled as far as man's mind could
go, but something far greater remained behind. Newton
sitting under his apple-tree and pondering on the wonderful
mechanism of the heavens, found the one great law which
accounts for the movements of all the bodies in the universe
— a law which explains equally why a pin falls to the ground
and why a comet which has been lost from sight for more
than a hundred years will return to a certain fixed spot at a
day and an hour which can be accurately foretold. " Kepler
had pointed out fixed and definite laws by which the uni-
verse is governed ; Newton demonstrated that one law ex-
plains them all. He showed us how one single thought, as
it were, of the Divine mind suffices to govern the most
complicated as well as the simplest movements of our
system.

1 84 SEVENTEENTH CENTURY, pt. m.

All this advance from Galileo to Newton was the work
of the seventeenth century. It began, you see, with certain
simple facts j by Galileo seeing that bodies existed in the
heavens which were not known to be there before ; it ended
in the beautiful law of which we have just spoken. But I
want you particularly to notice that this end would never
have been reached by men who were content to sit down
idly and talk of the greatness of God. It was the result of
real work by men who tried first to learn the facts, and from
these to prove reverently the way in which it pleases God to
bring them about ; and in this labour of love, being brought
face to face with the infinite grandeur of nature, they learnt
that true humility which led Newton, the greatest of them
all, to feel that he was but as a little child gathering pebbles
on the shore of the great ocean of truth.

Physics. — If we now turn to Physics, we shall find that
the way to knowledge lay still along the same road of patient
inquiry. Torricelli's barometer and Guericke's hemispheres
of Magdeburg both proved by direct experiment that the
atmosphere round our earth is pressing downwards with
great weight ; and this again brings us round to the force of
gravity, which is the cause of this weight; while Boyle's ex-
periment showed that air is elastic, being compressed in
exact proportion as the weight upon it is increased, and ex-
panding again directly it is diminished.

Again, in the subject of Light, we begin with hard dry
facts, which doubtless you may have thought it wearisome to
master, but we end with a theory so wonderful and beautiful
that it seems more like a fairy-tale than sober science. The
first step here was the invention of the telescope, which,
while it opened the road on the one hand to astronomical
discoveries, also led to the grinding of lenses, and to a more

CH. XXII. SUMMARY. 185

careful study of the laws of light. This it was which caused
Snellius to make experiments on the bending of rays with a
view to improving telescopes, and so to discover the law of
refraction, afterwards more fully stated by Descartes. Then
we find this last philosopher trying to explain the rainbow,
and studying the colours falling through a prism, and so the
subject passed on into the hands of Newton.

Here, by experiment again, the threads of light were dis-
entangled in the prism, and Newton drew out its many-
coloured rays, tracing them one by one on their road, till he
had shown that refraction explained them, and that to this
law, which seemed so uninteresting at first, we owe all the
lovely colours which surround us. And now Huyghens
takes up the story and leads us fairly into the invisible
world. This light, which Roemer had proved to be travel-
ling across space with marvellous speed, Huyghens shows
to be no actual substance at all, but most probably a
trembling of an invisible and intangible ether — a succession
of infinitely tiny waves chasing each other across millions of
miles, and striking at last on the minute opening of our eye,
bringing to us the wonderful effects of light. As Newton
traced colours, so Huyghens traces the invisible waves through
many substances, showing us their path and why they take
it j and landing us at last in the bewildering effects of polar-
ization, leaves us there to wait for more knowledge in a
future century.

Biology. — And now we come to Biology, or the study of
all those sciences which relate to life. Here you must re-
member that our account of the discoveries made, must be
more than usually imperfect, because the subject is more than
usually difficult. Yet we can form some idea of the new
light thrown upon the nature of the living body, by Harvey's

i86 SEVENTEENTH CENTURY. pt. hi.

theory of the circulation of the blood and the discoveries
which followed concerning the way in which nourishment is
carried to it. We can see how Mayow's experiments,
proving that part of the air is burnt within us, supplying heat
to our bodies, would have been a grand step in advance if
he had lived to make them more known, and how, indeed,
they did influence those who came after, though his name
was for a time forgotten. More clearly still we can under-
stand how Malpighi's and Grew's investigations with the
microscope, bringing to light hidden parts and vessels of the
human frame, gave rise to a totally new branch of science,
and enabled men to study the organisation of their own
bodies with an accuracy quite impossible before ; while the
same method applied to Botany gave the first real insight into
the structure of plants, tracing out their delicate organs, and
even the tiny cells of which their flesh is composed. And
lastly, in the field of Natural History, we find that Ray and
Willughby performed the immense task of classifying the
whole animal and vegetable kingdoms, and laid the founda-
tion of the grand generalizations of Linnaeus in the next
century.

SCIENCE OF THE
EIGHTEENTH CENTURY

Chief Men of Science in the Eighteenth Centtcry.

A.D.

Boei-hacave 1 668-1 738

Hales

I677-I76I

Haller

1 708-1 777

Hunter

1 728-1 793

Bonnet

1 720-1 793

Spallanzani

1 729-1 799

Buffon

I 707-1 788

Linnaeus

1707-1778

Lazzaro Moro

1687 —

Werner

1750-1817

Hutton

1 726-1 797

William Smith

%

1 769-1839

Black

. I 728-1 792

Bergmann .

• 1 735-1 784

Cavendish .

. 1731-1810

Priestley

I 733-1804

Scheele

. I 742-1 786

Rutherford .

1749-1819

Lavoisier .

. I 743-1 794

Watt .

. 1736-1819

Franklin

. 1 706-1 790

Galvani

. 1 737-1 798

Volta

. 1 745-1827

Maskelyne .

. 1732-1811

Lagrange .

1736-1813

Laplace

1 749-1827

Herschel

. 1 738- 1 822

CH. XXIII. DEVELOPMENT OF SCIENCE. 189

CHAPTER XXIII.

SCIENCE OF THE EIGHTEENTH CENTURY.

Great spread of Science in the Eighteenth Century — Advance of the
Sciences relating to Living Beings — Foundation of Leyden Univer-
sity in 1574 — Boerhaave, Professor of Medicine at Leyden, 1701 —
Foundation of Organic Chemistry by Boerhaave — Influence of Boer-
haave upon tlie study of Medicine — Belief of the Alchemists in
* Vital Fluids ' — Boerhaave's Experiments on the Juices of Plants —
Dr. Hales' Experiments on Plants — Boerhaave's Analyses of Milk,
Blood, &c. — Great popularity of his Chemical Lectures.

We have now arrived at the beginning of the eighteenth
century, only 175 years before our own day, when the dif-
ferent sciences which we have been tracing in their rise, Hke
little rills on the mountain sides, were beginning to swell
out into mighty streams, widening and spreading so rapidly
that it is in vain we strain our eyes to try and watch
them all. The time had now come when any man who
wished to be a discoverer was obliged to devote his whole
life to one branch of science, following it out in all its in-
tricate windings. And so we find that about this time each
science begins to have a complete history of its own, with
its own eminent men, and its peculiar language growing
more and more technical so as scarcely to be understood by
ordinary readers.

For this reason most general histories of Science stop at
this point and refer their readers to special works on the
different sciences. I do not, however, propose to do this ;

I90 EIGHTEENTH CENTURY. pt. hi.

for though I must warn you again more strongly than ever
that I can only give you little glimpses of the work that was
being done, still I think that if we struggle on through the
increasing mass of knowledge and gather up a fragment here
and there, you will gain a general idea of the progress of
science, and be able to read more advanced scientific books
with much greater interest, even though you may have
learnt very little of any one science.

Astronomy, Physics, and to a certain extent Chemistry,
had made such a start at the end of the seventeenth century
that it was a great many years before those men who came
after Newton, Halley, Huyghens, and Stahl, had mastered
the new discoveries sufficiently to progress any further.
Therefore we find that it was not in these sciences that most
advance was made in the beginning of the eighteenth cen-
tury, but in those which relate to living beings, and which
are all included under the head of Biology, or the science of
life. Medicine, Anatomy, and Physiology were the branches
which grew -most rapidly about this time ; and the five great
men whose names stand out most conspicuously are Boer-
haave, Haller, John Hunter, Bonnet, and Spallanzani :
Boerhaave, as the founder of the study of organic chemistry,
Haller and Hunter as the fathers of coinparative anatomy,
and Bonnet and Spallanzani as the discoverers of some very
remarkable facts m physiology. We will take these subjects
in regular order, and try to understand something of the
work which was done in them.

Medical School of Leyden Foundation of Organic

Chemistry by Boerhaave, 1701. — On the coast of Holland,
just where the Rhine empties itself by a number of small
channels into the German Ocean, stands the city of Leyden,
which became famous in the year 1574, on account of a

CH. XXIII. HERMANN BOERHAAVE. 191

siege of four months which the starving inhabitants endured
with the utmost heroism, when the Protestant Netherlanders
were struggHng for Hfe and Hberty against PhiHp II. of Spain.
The Dutchmen were successful at last and drove out the
Spanish army, by cutting away the dykes and letting the sea
swallow up their beautiful pastures, their neat villages, and
their fruitful orchards ; and as a reward for their devotion to
the cause, William of Orange founded the University of
Leyden, which afterwards became very celebrated.

Hermann Boerhaave, of whose work we are now going
to speak, was a Professor of Medicine in this University
about a hundred years after its commencement. The son
of a Dutch clergyman, he was born in 1668 at Vorhout, one
of those same small Dutch villages near Leyden which had
been for days under the sea in 1574. His father intended
him for the church ; but the young student, having been
accused of holding false opinions, was only too glad to give
up this profession and study medicine, in which he de-
lighted. He was so successful that in 1701 he was made
Lecturer of Medicine in the University, and a few years
later the Professorships of Chemistry and Botany were
also given to him. From that time the Medical School of
Leyden became famous all over the world. Students
flocked to it from all quarters, and most of the best me-
dical men of Europe were pupils of Boerhaave. This was
due chiefly, of course, to his wonderful medical knowledge
and his skill as a lecturer ; but his popularity was greatly
increased by his enthusiasm, kindly temper, and the great
interest which he took in the success of his pupils. He
was always ready to help others and to give them credit
for the work they had done, and it is said that even his
enemies could not resist his constant and uniform kind-

192 EIGHTEENTH CENTURY. pt. hi.

ness and good-temper. He loved his science too well to
hinder its progress by angry disputes ; and by imparting
this spirit to his pupils he did almost as much for the
spread of medical science as by the facts which he taught
them.

But besides his influence upon medicine in general there
was one particular study which Boerhaave may be said to
have founded j this was the chemistry of living substances,
or organic chemistry. You will remember that the false
science of alchemy had always been much mixed up with
chemistry, and the alchemists had some strange mystical
notions about * vital fluids/ which they supposed to exist in
animals and plants, and to cause their life and growths Little
by little, however, more correct ideas had grown up in the
1 6th and 17th centuries about the nature of life. Vesalius,
Harvey, Malpighi, Grew, and many others, had gradually
described more and more accurately the working of the dif-
ferent organs of a living being, and now Boerhaave went
farther, and tried to discover by means of chemistry of what
materials these organs themselves are composed.

In the same way that Geber had decomposed or divided
up inorganic substances, such as metals and earths, by distil-
lation and sublimation (see p. 44), so Boerhaave proposed to
decompose the organic substances of which plants and ani-
mals are made, and to discover the materials contained in
them. To accomplish this he took a plant, such as rosemary,
and puttiiig fresh moist leaves of it into a furnace, heated
them gently and drove out all the moisture, which he col-
lected in a separate vessel. When this moisture had cooled
down into a liquid he examined it and found that it was
made up of water, and of different kinds of oils and
essences, according to the plant he had taken. For in-
stance, from rosemary he got an essence with the peculiar

CH. XXIII. ORGANIC CHEMISTRY. 193

scent of rosemary ; from the bark of the cinnamon \xQQ,Laurus
Camphorum, or Cinnamomum camphoi'um^ he got essence of
cinnamon ; from its roots, camphor ; and from its leaves an
oil with the taste of cloves. Then after he had extracted
all the juice from the plant, he burnt the dry remains, to see
what would be contained in its ashes after the fire had
driven off part of the solid matter as gas, and he found in
them a kind of salt, which was also different in different
plants. But if he poured hot water on the plant before
burning it, he found no salt in the ashes, for it had been
dissolved and carried off in the water.

Having now found what substances were in the plant,
the next step was to discover where they came from ; so he
took several specimens of earth in which plants can grow
and examined them also ; and he found that he could
extract from them many of the substances, such as salt,
alum, borax, and sulphur, which he had also discovered in
the ashes of the plants. It was clear, then, that the plant
took these salts out of the earth ; and by a number of experi-
ments he went on to prove that they are dissolved by the
rain-water which sinks into the earth, and are then sucked
up by the plants through their roots and carried up to the
leaves, where they are exposed to the air and sunshine, and
altered so as to become food for the plant The other
parts which did not come from the soil he concluded must
be taken in from the air. These were splendid facts, and
curiously enough a celebrated English chemist. Dr. Hales
(born 1677, died 1761), made some of the same experi-
ments almost at the same time, which confirmed those of
Boerhaave. Hales even went so far as to measure the
quantity of water taken in at the roots and given out at
the leaves of plants, and he discovered the way in which
10

194 EIGHTEENTH CENTURY. pt. ill.

plants breathe through the httle stomata^ or mouths, disco-
vered by Grew (see p. 141).

From the juices of plants Boerhaave next went on to
those of animals, and he decomposed in a most beautiful
and simple manner milk, blood, bile, and those fluids called
chyle and lymph which convey nourishment to the blood.
These he compared with the sap, gums, resins, and oils of
* plants, and showed that animal bodies are made up of
altered vegetable matter, just as plants are in their turn
composed of ma<tter taken from the soil and the air; and
he suggested that by careful experiments it would at last be
possible to discover exactly the materials of which all living
beings were made.

Boerhaave's analyses of organic substances were very
rough and imperfect compared to those which are made now;
for you must remember that the four gases, oxygen, hydro-
gen, nitrogen, and carbonic acid, which we now know are the
chief constituents of plants, were not yet discovered. Yet
even these rough attempts were so interesting that students
crowded round the doors of his lecture-room for hours
before the lecture began, to secure admission ; and there can
be no doubt that his ' Elements of Chemistry,' published in
1732, contained the first steps in the study of the chemistry
of living things. Boerhaave was also a celebrated botanist.
He died in 1738, and deserves always to be remembered as
one of the greatest teachers of the eighteenth century.

Chief Works consulted. — Brewster's 'Encyclopsedia ' — 'Boerhaave ;'
Cuvier, * Hist, des Sciences Naturelles ; ' Sprengel, ' Hist, de la Medi-
cine,' 181 5 ; Burton's *Life and Writings of Boerhaave,' 1746 ; Boer-
haave, 'Elements of Chemistry,' Englished by Dallo we, 1735 ; Miller's
'Chemistry ;' Hales' 'Essays concerning Vegetable Staticks,' 1759.

CH. XXIV. HALLER— ANATOMIST. 195

CHAPTER XXIV.

SCIENCE OF THE EIGHTEENTH CENTURY (CONTINUED).

Childhood of Haller — Foundation of the University of Gottingen in
1736 — Haller made Professor of Anatomy — Haller's Anatomical
Plates — He discovers the power of Contraction of the Muscles —
Rise of Comparative Anatomy — ^John Hunter's industry in Dissect-
ing and comparing the Structures of different Animals — His
Museum and the arrangement of his Collection — Bonnet's Experi-
ments on Plants — Experiments upon Animals by Bonnet and
Spallanzani — Regrowth of different parts when cut off — Bonnet's
theory of Gradual Development of Plants and Animals — Anatomical
Works of Haller — He discovers the power of the Muscles to con-
tract.

Haller, 1708-1777.— Among the pupils of Boerhaave there
was one man who became, if possible, even more famous
than his master. This was Albert von Haller, son of the
Chancellor of Baden, who was born at Berne in 1708, and
died in 1777. Haller seems to have been a most extra-
ordinary child \ at nine years of age it is said that he knew
Latin and Greek, had made a Hebrew and Greek dictionary,
a Chaldean grammar, and an historical dictionary ! We
are not told how good these books were ; but how very few
boys of nine years old would have been able to write them
at all ! At seventeen Hallef went to Leyden to study under
Boerhaave, and under Albinus, a famous anatomist j and
at nineteen he was already a doctor of medicine. Having
been driven out of Paris because the people were horrified

196 EIGHTEENTH CENTURY. pt. hi.

at his dissecting dead bodies, he went to Berne, where he
became professor of anatomy; and in 1736, when George
II. of England, who was also Elector of Hanover, founded
the University of Gottingen, he went there as professor of
anatomy, surgery, and botany, and soon made that Univer-
sity as famous as Boerhaave had made Leyden.

One of his first reforms was to turn the work of his pupils
to good account. When medical students are going to pass
their last examination they are required to write an essay, or
thesis, as it is called, before they can receive their degree of
doctor. Haller used always at these times to propose to
each one of his students some difficult point in anatomy or
physiology, in which he thought new discoveries might be
made, and he then drew out a plan for them and showed
them how to begin. By this means their essays were often
full of new and useful information, and it was a great deal
owing to the help of his pupils that Haller was able to
publish 180 volumes on science, all more or less valuable.

There was also a very good anatomical theatre at
Gottingen, and from dissections made there Haller produced
a set of most beautiful anatomical drawings, which he pub-
lished between 1743 and 1753. You will remember that
Vesalius published many fine engravings of parts of the
human body (see p. 67), and since his time many others
had been made, especially by Haller's master, Albinus. But
Vesalius' drawings were coarse, because he had no micro-
scope to help him, and Albinus had only drawn separate
parts, such as a muscle, a nerve, or a vein. Haller's plates
were the first which showed the different nerves and vessels
attached in their right position, and to each plate he added
a complete history of the function, or use of the parts
drawn. He made these drawings so accurate, and spent so

CH. XXIV. COMPARATIVE ANATOMY. 197

much time upon each minute structure, that in seventeen
years, with all the help he had, he was not able to complete
the description of the whole human body.

Haller discovers the Power of the Muscles to Contract.
— It was while he was at work at these dissections that he
made one great discovery, which you must try to understand.
If you clasp your right hand round your left arm, just above
the elbow, and then bend your left arm, you will feel the
part under your hand swell up and grow hard. The reason
of this is that the muscle of your arm, called the biceps, has
contracted, or grown shorter and thicker, in the process
of bending your arm. If you open your arm again, the
swelhng will go down, because the muscle is stretched out.
Now before Haller's time it was thought that the muscles
could not contract of themselves, but were drawn up by the
nerves. Haller discovered that this is not so, but that a
muscle, if irritated, will draw itself together even when it is
quite separated from the nerves, and this has since been
proved to be true by a great number of experiments. So
that though it is true that our nerves are the cause of our
I moving, because they excite the muscles and so make them
contract, yet the real power of contraction is in the muscle
itself.

Comparative Anatomy, or the Comparison of Different
Structures in Men and Animals. — John Hunter. — Another
point in which Haller did good service to science was in
comparing the same parts of the body of men and animals,
and showing how far they are alike. This study, which is
called the study of comparative anatomy, has now become
very important, for by examining any organ, such as the
heart for example, from the lower animals in which it is
very simple, up to man in whom it is complicated, we can

198 EIGHTEENTH CENTURY. pt. hi.

trace its gradual improvement, and understand it much more
perfectly. Aristotle and Vesalius had both of them com-
pared some of the parts of different animals, and so had
other and later zoologists ; but Haller was the first to make
it a regular study, and John Hunter, who lived about the
same time, devoted his whole life to it, and raised it to the
rank of a separate science.

John Hunter, who was born in the County of Lanark,
in 1728, was the brother of a very eminent London phy-
sician, Dr. William Hunter, who was also a great anatomist.
John, being delicate, had been allowed to grow up with very
little education, and at twenty years of age he came up to
London, a mere ignorant lad, to try and help his brother in his
anatomical dissections. Here he soon showed that he had
plenty of ability, for he learnt dissecting so rapidly that at
the end of a year he was able to teach his brother's pupils,
and before long he became one of the leading surgeons at
St. George's Hospital, and had a large private practice.

But though he made a great deal of money by his pro-
fession, he spent it all upon his favourite study of anatomy,
to which he devoted every spare moment. His great wish
was to compare thoroughly the different parts of men and
animals, so as to show how the life of each one of them is
carried on. For this purpose he dissected and preserved in
different ways the bodies of all the animals he could lay his
hands upon. He bought up all the wild beasts that died in
the Tower, where they were then kept, and any which he
could procure from travelling menageries, and he even kept
foreign animals himself in a piece of ground at Earl's Court,
Brompton, that'he might watch their habits and dissect their
dead bodies.

As years went on and his specimens increased he built a

CH. XXIV. HUNTER'S MUSEUM. 199

large museum in Leicester Square, and arranged his collec-
tion so as to show which parts in different animals serve for
the sa.me use. For example, to illustrate the way in which
animals digest their food, he placed first the hydras, polyps,
and sea-anemones, which are all stomach, being in them-
selves nothing but a simple bag surrounded by little feelers,
and having a fluid inside which dissolves the food. Then
he arranged in order many forms up to the leech, which is
a bag with two openings, and has a head and nerves and
other parts, besides a stomach. Then came the insects,
some of which, as the bees, have a separate receptacle for
honey, of which they disgorge a part and then pass on the
rest into the real stomach. Then came the snails, in which
the stomach is a separate part with a second opening to
pass out the food it cannot take up. Then the fishes, some of
whom have stomachs strong enough to crush the shells and
indigestible parts of their food, while others have the mouth
lined with teeth for this purpose ; then came the stomachs
of reptiles ; and afterwards those of birds, with the curious
crop where the food lies first, and the gizzard, in which it is
rubbed against the little stones which the bird swallows.
Then finally came the stomachs of the higher animals, with
many curious and interesting peculiarities ; as for example,
the divided stomach of those animals, such as the calf, which
chew the cud, and of the camel, in which one division serves
as a water-bag. And side by side with these organs of
digestion he placed the teeth of each animal, showing how
these were each exactly fitted to prepare the food for the
particular kind of stomach of the animal to which they
belonged.

In this way Hunter tried to arrange the history of all the
different organs of the body, tracing out each as perfectly as

200 EIGHTEENTH CENTURY. pt. hi.

he could, and showing how it suited the wants of the various
animals. His museum cost him an immense amount of labour,
and more than 70,000/. in money ; when he died, in 1793, it
was bought by the English Government for 15,000/. and
placed in the London College of Surgeons, and for the last
eighty years many a London student of physiology has had
occasion to be thankful to the rough and uneducated John
Hunter for the laborious and careful work he did, and the
magnificent collection he left behind him.

Experiments upon Animals by Bonnet and Spallanzani.
— ^While Haller and Hunter by their dissections were adding
greatly to our knowledge of the structure of animals, two
famous naturalists in Switzerland and Italy were bringing to
light some extremely curious and interesting facts about their
growth.

The first of these, named Charles Bonnet, was born at
Geneva in 1720, and died in 1793. He had a great love of
natural history, and when he was twenty years of age he
wrote a paper upon aphides^ or plant-lice, which was so re-
markable that the French Academy of Sciences at once
elected him one of their corresponding members. He
also made some very interesting experiments upon plants,
showing that they have the power of seeking out for them-
selves what is necessary for their growth. We all know that
plants grow towards the light, and if kept in a dark room
will seek out even a crack through which the light comes.
But Bonnet proved that they will do much more than this,
for he found that if he twisted the branch of a tree so as to
turn the leaves bottom upwards, in a little time each leaf
turned right round on its stalk so as to get back into its
natural position ; while on the other hand, if he hung a wet
sponge over a leaf, the leaf would turn its under side up-

CH. XXIV. BONNET AND SPALLANZANI. 201

wards, so as to bring the little mouths, or stomata, close to
the sponge, and enable them to drink in the water. In this
way a plant will always find out the best way of growing so
as to get as much sun and food as it can. Many curious
facts of this kind were published in Bonnet's work on the
' Use of the Leaves of Plants,' but what I wish now particu-
larly to relate to you are his experiments upon animals and
the regrowth of limbs which had been cut off.

It had long been known that very simple organisms, such
as polyps, may be cut in pieces, and each part will live and
become a perfect creature ; but no one thought it possible
that any of the more complicated living beings could be
treated in this way. Bonnet, however, and the famous
Italian naturalist Spallanzani (i 729-1 799) proved by a great
number of experiments that tails, legs, and even heads will
grow again in some animals after they have been cut off.
The garden-worm, for example, is an animal with many
organs : it has numerous bristles, which serve as feet, it has
arteries and veins, nerves, and organs of digestion, and a
mouth ; yet Bonnet found that a worm if cut in pieces would
grow a new head or a new tail, and, what was still more
curious, in some .rare cases it grew the head on the end where
the tail had been before I

Spallanzani went even farther than this, for he experi-
mented on snails. Now the common garden snail has a
head with four horns, moved by very complicated muscles,
and two of these horns have eyes at the end of them j more-
over it has a mouth, with teeth and a tongue. Spallanzani
cut off first the horns with eyes, and afterwards the mouth
and tongue, and found that the snail had power to re-grow
them all. He then tried upon aquatic salamanders, which
resemble our newts, or efts. These creatures have red blood

202 EIGHTEENTH CENTURY. pt. hi.

like ourselves, they have a heart, lungs, bones, and muscles,
and their legs possess muscles and nerves like those of a
man ; yet Spallanzani cut off the tail and legs of one sala-
mander six times in succession, and in another case. Bonnet
cut them off eight times, and they grew again. Bonnet even
took out the right eye of a newt, or eft, and in eight months
another eye had grown in its place. These experiments were
very startling, for they showed that the life of the lower
animals does not depend on a particular part of the body so
much as it does in ourselves and in the higher animals. If
you cut off the head of a man or an ox, they die, or if you
cut off a leg, it never grows again ; but these experiments
proved that the worm and the snail live and grow new heads
and limbs, and that the more simple an animal is, the more
power it has to live and grow after it is cut in pieces.

These discoveries led Bonnet to make a suggestion which
I want you to remember, because we shall have to speak of
it by-and-bye. He asked whether it was not likely that
there was a gradual development or complication of the
parts of the body as you ascend from the lowest plant up to
the highest animal, so that the body of a worm, for example,
could do all the work necessary to keep it alive and to make
it grow, without the help of its head, and a lizard could in
the same way make a new leg without much difficulty. But
as the machinery grew more and more complicated this would
not be so easy, till at last it would become impossible in the
higher animals, just as in a complicated machine one broken
wheel will upset the whole working. Bonnet wrote a book
called ' The Contemplation of Nature,' in which he dwelt
upon this subject, and tried to trace out how animal forms
had become gradually higher and higher, till they had arrived
at man. We shall see by-and-by how this idea occurred also

CH. XXIV. DEVELOPMENT OF ANIMALS. 203

to the naturalist Lamarck, and how it has become the founda-
tion of a grand theory of Ufe in the present century. Mean-
while you must bear in mind that Bonnet and Spallanzani
added enormously to our knowledge of the lower animals
and their powers of life, and together with Boerhaave,
Haller, and Hunter did a great deal to advance the sciences
of anatomy and physiology in the beginning of the eighteenth
century.

Chief Works consulted. — 'Life of Haller' — 'Naturalists' Library;'
Brewster's 'Encyclopaedia,' arts. 'Physiology' and 'Haller ;' Lawrence's
'Lectures on Comparative Anatomy,' 1816 and 1848; Lawrence's
translation of Blumenbach's 'System of Comparative Anatomy,' 1807 ;
* Life of John Hunter ' — ' Naturalists' Library,' vol. x. ; Cuvier, 'Hist,
des Sciences Naturelles ;' Carpenter's ' Comparative Physiology ; ' Tom
Taylor's ' Leicester Square,' Appendix by Professor Owen.

204 EIGHTEENTH CENTURY. pt. hi.

'U

HAPTER XXV.

Birth a )d Early Life ot Bulfon and Linnaeus compared — BufFon's
Work Dn ISaturai History — Daubenton wrote the Anatomical Part
— Buflbn's Books very interesting, but not always accurate — He first
worked out tne Distribution of Animals — Stniggles of Linnaeus
with Poverty — Mr. Clifford befriends him — He becomes Professor at
Upsala — He v«-as the first to give Specific Names to Animals and
Plants — Explanation of his Descriptions of Plants — Use of the
Linnasan or Artificial System — Afterwards superseded by the Natural
System — Linnaeus fii'st used accurate terms in describing Plants
and Animals — Character of Linnaeus — Sale of his Collection, and
Chase by the Swedish Man-of-war,

Advance of Natural History — Buffon and Linnaeus. — In

the year 1707 two men were born, the one in France and
the other in Sweden, whose names have become almost
equally well-known, although they were by no means equally
great.

The Frenchman, George-Louis Le Clerc Buffon, the son
of a counsellor of the parliament of Dijon, was bom on his
father's estate in Burgundy. The Swede, Karl Linnaeus, the
grandson of a peasant and son of a poor Swedish clergy-
man, was born in a small village called Rashult, in the south
of Sweden. Buffon enjoyed the best education which
France could afford him, with plenty of opportunity to culti-
vate his love of natural history. At one-and-twenty he
succeeded to a handsome property, and after travelling foi
some time settled down to a life of ease and Hterature, partly

CH. XXV. BUFFON'S NATURAL HISTORY. 205

in Paris, and partly on his estate in Burgundy. Linnaeus
was taught in a small grammar-school, where he showed so
little taste for books that his father would have apprenticed
him to a shoemaker if a physician named Rothmann, who saw
the boy's love of antural history, had not taken him into
his own house and taught him botany and physiology. At
one-and-twenty, when Buifon came into his fortune, the
young Linnaeus, with an allowance of eight pounds a year
from his father, was a struggling student at the University of
Upsala, putting folded paper into the soles of his old shoes
to keep out the damp and cold.

Buffon's work on Natural History : he traces the
Distribution of Animals. — Buffon's private life is not
interesting. He was a vain man, and not a moral one ; but
he had great talents, and remarkable perseverance and
industry. In 1739 he was appointed Superintendent of the
Royal Garden and Cabinet at Paris, a position which he
held till his death. His great work, of which we must now
speak, was his ' Natural History,' which occupied him the
greater part of his life. It is one comprehensive history of
the living world, containing descriptions of all the animals
then known, their structure, their distribution, their habits,
and their instincts, and, mingled with these, many curious
theories about the world and its inhabitants.

The anatomical part of this work was done by a physician
named Daubenton, who came from Buffon's own village, and
was appointed keeper of the cabinet of natural history
through his influence. Buffon was very fortunate in having
the help of this man, for having weak sight himself, and
being more fond of general theories than of petty details,
this part of his work would have been very poor if it had
not been for Daubenton's careful and conscientious dis-

2o6 EIGHTEENTH CENTURY. pt. in.

sections and descriptions. The rest of the work was written
chiefly by Buffon himself, who bestowed upon it immense
pains and labour. He was a very pleasing writer, and did a
great deal for natural history by making it popular. His
books were more like romances than works of science, but
he collected in them a great deal of very useful information,
and put it in a shape which everyone could read with
pleasure, and in this way led people to think, and to wish to
know more about natural history and the habits and lives
of animals. He was also the first to trace out with any care
the way in which animals are distributed over different parts
of the globe; how they are checked by climate, by
mountains, by rivers, and by seas from wandering out of
their own regions, and how they are more widely spread
over cold countries than over warm ones, because they are
able to cross the seas and rivers upon solid or floating ice,
and so get from one region to another.

In this general way Buffon gathered together a great
many interesting facts about animals. His works were all
the more popular because he disliked anything like classi-
fication. He would not attempt to group the animals after
any particular method, but liked to describe each one with
a little history of its own, and to write on freely without any
very great scientific accuracy. Of course the consequence
was that he often made great mistakes, and arrived at false
conclusions ; still he had so much genius and knowledge
that a great part of his work will always remain true, and
Natural History owes a great deal to Buffon. He died in
1788, in the eighty-first year of his age, and twenty thousand
people assembled to do him honour at his funeral.

Life and Influence of linnseus, 1707-1778. — We must
now turn to Linnaeus, whose whole life and labours were as

CH, XXV. EARLY LIFE OF LJNNMUS, 207

different from those of Buffon as his birth and early life had
been. Buffon hated to be bound down to exact details ;
Linnaeus found his greatest pleasure in tracing out each
minute character in plants and animals so accurately as
to be able to build up a complete classification, by which
anyone could tell at once to what part of the animal or
vegetable kingdom any living being belonged. While Buf-
fon's books were entertaining and readable, Linnseus's were
often hard dry science, consisting chiefly of long accurate
tables and minute details about the structure of animals and
plants. Yet Linnaeus's writings are worth infinitely more
than those of Buffon's for one simple reason, he had a more
earnest love of t7'uth.

Linnaeus seems to have been bom a botanist. He writes
in his own diary that when he was four years old he went to
a garden party with his father and heard the guests dis-
cussing the names and properties of plants ; he listened
carefully to all he heard, and ' from that time never ceased
harassing his father about the name, quality, and nature of
every plant he met with,' so that his father was sometimes
quite put out of humour by the incessant questioning.
However at last, when Dr. Rothmann took him into his
house, he had opportunities of learning, and firom that time
he advanced so rapidly that he was soon beyond all his
teachers.

In 1736, after meeting with many kind friends in his
poverty, and making a journey to Lapland, which was paid
for by the Stockholm Academy of Science, he went to
Holland. Here he called on the celebrated Boerhaave, who
with his usual good nature introduced him to a rich banker,
named Clifford, who was also a great botanist. This was
the turning-point of Linnaeus's life. Mr. Clifford invited

2o8 EIGHTEENTH CENTURY. PT. ill.

him to live with him, treated him Hke a son, and allowed
him to make free use of his magnificent horticiilutral garden.
He also sent him to England to procure rare plants, and
gave him a liberal income. This continued for some time
till Linnseus's health began to fail, and he found besides
that he had learnt all he could in this place, so he resolved
to leave his kind friend and wander farther. Mr. Clifford
seems to have been much hurt at his leaving, yet he con-
tinued his kindness to him through life.

Linnaeus went to Leyden and Paris, and from there to
Stockholm, where he practised as a physician, and at last he
settled down as Professor of Medicine and Natural History
at Upsala, where he founded a splendid botanical garden,
which served as a model for many such gardens in other
countries, such as the Jardin de Trianon in France, and
Kew Gardens in England. His struggles with poverty were
now over for ever, and his fame as a botanist was spread all
over the world. He used to set out in the summer days
with more than 200 pupils to collect plants and insects in
the surrounding country, and many celebrated people came
to Stockholm to attend Linnseus's ' Excursions.' Then as his
pupils spread over the world he employed them to collect
specimens of plants and animals from distant countries, and
he himself worked incessantly to classify them into one
great system.

Liimseus gives Specific Names to Plants and Animals.
— And now we must try to seize upon the chief points of
Linnseus's work, that you may be able to understand some-
thing of what he did for science, although it is quite impos-
sible for us to give even a sketch of his divisions of the
animal and vegetable kingdoms. The first and greatest
point of all was that he gave a second or specific name to
every plant and animal. Before his time botanists had

cii. XXV. LINN^US ON SPECIES. 209

only given one name to a set of plants ; calling all roses, for
example, by the name Rosa, and then adding a descrip-
tion to show which particular kind of rose was meant.
Thus, for instance, for the Dog-rose they were obliged to
say Rosa, sylvestris vulgaris, flore odorato incarnato, that is,
'common rose of the woods with a flesh-coloured sweet-
scented flower.' This, you will see, was extremely incon-
venient ; it was as if all the children in a family were called
only by their father's name, and you were obliged to describe
each particular child every time you mentioned him ; as
' Smith with the dark hair,' or ' Smith with the long nose and
short fingers,' &c. A botanist named Rivinus had suggested
in 1690 that two names should be given to plants, and
Linnaeus was the first to act upon this idea and to give a
second specific, or, as he called it, trivial name to each par-
ticular kind of plant, describing the plant at the same
time so accurately that anyone who found it could decide at
once to what species it belonged. To accomplish this he
classified all plants, chiefly according to the number and
arrangement of their stamens and pistils (or those parts
which produce the seeds), and then he subdivided them
by the character and position of their leaves and other parts.
In describing the geranium, for example, he mentions
first the ' sepals,' or little green leaves under the flower ; he
says they are five, and very pointed ; then the ' petals,' or
flower-leaves, are five also, growing on the sepals and
heart-shaped ; the * stamens ' are ten in number, and grow
separate ; the little vessels on the top of the stamens, which
are called * anthers,' and hold the yellow dust, are oblong ;
the 'pistil,' or seed-vessel, is formed of five parts, which
are joined together into one long beak which ends in five
points j the seeds are covered with a skin and are shaped

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like a kidney, having often a long tip which is rolled round
in a spiral (like a corkscrew). Here we have a definition
of the ge?ius geranium \ but many geraniums will answer to
this description, so he goes on to describe some more
special characters. The sepals in this particular specimen,
he says, are joined together in one piece \ the stem of the
plant is woody, the joints are fleshy, the leaves are slightly
feathered at the edge. These last characters are peculiar to
this kind of geranium, which he calls .Geraniu7n gibbosum,
and here we have the specific name. Any geranium which
has the woody stem, the joined sepals, the fleshy joints,
and the feathery-edged leaves, will be the species called by
Linnaeus gibhosMin.

You will see that by this system it is always possible to
find out easily to what part of the vegetable kingdom your
plant belongs and what its name is ; and if, after you have
traced its genus, there is no species which exactly agrees
with yours, you then know that you have discovered a new
species which has not been described before. Linnaeus
classified animals after this same plan, quadrupeds chiefly by
their teeth, and birds by their beaks, and after his system
was complete anyone could discover the scientific name of a
plant or animal by exercising a little care and patience.
This system is called the Linnaean, or artificial system^ be-
cause it only selects a few particular parts of a plant, so
as to help you to look it out in a kind of dictionary. It tells
you very little of the real or natural life of the plant, and
often brings some very near together which are really very
different. It is as if you classified people by some par-
ticular feature, such as those who had long hair, or short
hair, dark or light, curly or straight. This might be very
useful for recognising them, but it would be quite artificial.

CH. XXV. LINN^AN SYSTEM. 211

and would tell you very little about their real relationship.
Therefore this classification has now been partly set aside
for another or natural classification, which Linnaeus also
suggested, only he thought it too difficult for ordinary people ;
and which was worked out by a French botanist named
Jussieu, as we shall see by-and-by. But the Linnsean
system is still extremely useful for finding the name of a
plant or animal, and many people in the last century were
led to study zoology and botany by the simplicity of the
classifications of Linnaeus.

The other useful point in Linnaeus's system was the
accurate and precise terms he invented for describing plants.
Before his time naturalists used any words which suited
them, and as different people have often very different ideas
as to what is meant by long or short, round or pointed, &c.,
the descriptions were often of very little value. , But
Linnaeus could not work out his system without using very
clear terms and explaining beforehand what he meant by
them ; and as his nomenclature, or system of names, was soon
followed in other countries, botanists in all parts of the
world were able to recognise at once what was meant by the
description of any particular plant. The same advantage
arose out of his classification of animals, and the care with
which he traced out their chief characters. I wish I could
have given you some idea of this system, which was fully
explained in the ' Systema Naturae,' completed in 1768. But
when you remember that Linnaeus classified minutely the
whole of the animals and plants known in the world, you
will perceive that I should have to write a separate book to
make you understand it. If you can only remember that he
did build up this artificial system, and that he was the first to
give specific names to plants and animals and to create an

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accurate nomenclature all over the world, you will, I think,
have learnt as much as you need at present about the work
of the great Swedish naturalist.

Linnaeus was not a vigorous old man. The hard
struggles of his youth and the immense work of his after-
life had worn him out, and at fifty-six he was obliged to ask
the King of Sweden to let his son lecture sometimes in his
place. AVith this help he continued to work at science till
within two years of his death, when his mind became feeble.
He died in 1778, loaded with honours and beloved and
esteemed by the greatest men all over the world. His had
been a noble life \ enthusiastic and truth-loving, he had
worked, even when he was poor, for science and not for
wealth, and when he became famous and rich he helped his
pupils as others had helped him, and lived simply and
frugally till his death. Unlike Buffon, his private life was as
pure as his public life was famous. Over the door of his
room he placed the words ^ Innocue vivito, Numen adest^
(' Live innocently, God is present '), and he lived up to his
motto. His study of nature had filled him with deep
reverence and love for the Great Creator, and he used often
to tell his friends how grateful he was to God for those gifts
which had made his life so full of interest and delight.

After the death of Linnaeus his mother and sisters sold
his collection of plants and insects, and all his books and
manuscripts, to Dr. Edward Smith (afterwards Sir E. Smith),
for one thousand pounds. The King of Sweden was at this
time away from Stockholm, but directly he returned and
heard that such a valuable national treasure was on its way
to England he sent a man-of-war to try and bring it back.
A very amusing chase then took place ; Dr. Smith did not
mean to lose his prize if he could help it, so he set full sail

CH. XXV. LINNAiAN COLLECTION. 213

and literally ran away till he reached the Thames, and
landed safely in London without being caught. Thus the
Linnsean collection came to England, and is now in Bur-
lington House. The Swedes are naturally sorry that it left
their country, but on the other hand it has become more
known to scientific men in London than it could ever have
been in Stockholm. With Linnaeus we must end for the
present the history of the sciences relating to living beings.
Early in the nineteenth century we shall return to them
again, but in the next chapter we must learn something of a
new science which arose about this time ; namely, the
science of ' Geology,' or the study of the earth.

Chief Works consulted. — ^Jardine's ' Naturalists' Library,' vols. ii. and
xiii. ; Brewster's * Encyclopaedia ' — ' BufFon and Linnseus ; ' Cuvier,
* Histoire des Sciences Naturelles;' Smith, Sir J., 'Introduction to
Botany ; ' Pulteney's ' View of Writings of Linnseus j * Linnaeus,
' Systema Naturae. '

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CHAPTER XXVI.

SCIENCE OF THE EIGHTEENTH CENTURY (CONTINUED).

The Study of the Earth neglected during the Dark Ages — Prejudices
concerning the Creation of the World — Attempts to Account for
Buried Fossils — Palissy, the Potter, first asserted that Fossil-shells
are real Shells — Scilla's Work on the Shells of Calabria, 1670 —
Woodward's Description of Different Formations, 1695 — Lazzaro
Moro one of the first to give a true explanation of the facts — Abra-
ham Werner lectures on Mineralogy and Geology, 1775 — Disputes
between the Neptunists and Vulcanists — Dr. Hutton first teaches
that it is by the Study of the Present that we can understand the
Past — Theory of Hutton — Sir J. Hall's Experiments upon Melted
Rocks — Hutton discovers Granite Veins in Glen Tilt — William
Smith, the * Father of English Geologists ' — His Geological Map of
England.

Early Prejudices concerning the Formation of the
Rocks. — You will no doubt remember that when we were
speaking of the science of the Greeks, we learnt (p. 11) that
Pythagoras made many interesting observations about the
crust of the earth, which led him to say that the sea and
land must have changed places more than once since the
creation of the world. Especially he pointed out that sea-
shells are found inland; deeply buried in the hills ; and that
the sea eats away land on the coast in some places, while in
others earth is washed down by the rivers and laid at the
bottom of the ocean.

We have now passed over more than 2,000 years since
the time of Pythagoras, and you will notice that we have

CH. XXVI GEOLOGY 215

heard nothing more about observations of this kind. The
fact is, that during the Dark Ages the study of the earth had
been ahnost entirely neglected, and people had taken up the
mistaken notion that they ought to believe, as a matter of
faith, that the world was created in the beginning just as we
now see it. But knowledge and inquiry were advancing so
fast in the eighteenth century, that it was impossible for such
ignorance to continue long. People could not go on digging
wells and making mines in all parts of the world without
being struck by the way in which the different strata^ or
layers of rock, are arranged in the earth's crust, nor without
noticing the fossil shells, plants, and bones of animals which
they found buried at great depths.

At first they were very unwilling to believe that these
remains had ever belonged to living animals and plants, and
they tried to imagine that they v/ere only stones resembling
shells, leaves, &c., which had been in some way mysteriously
created in the earth. Then, when this absurd idea was
given up, they next enquired whether a universal flood
might not have spread them over the land ; but though this
opinion was upheld for more than a hundred years, yet it
Avas clear to all those who really studied the subject that it
could not account for the many layers of fossils deeply
buried in the earth.

First Attempts to study the Fossil Remains and the
beds containing them. — At last, little by little, there arose
men who adopted the more sensible plan of studying the
different formations in the crust of the earth before making
theories about them. Bernard de Palissy, the maker of the
famous French pottery, was the first to assert, in 1580, that
the fossil shells were real sea-shells left by the waters of the
ocean; then, in 1669, we find Steno, a Dane, writing a re-

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markable work on petrifactions in the rocks; and in 1670
Scilla, an Italian painter, published a treatise on the fossil
shells and other remains in the rocks of Calabria, and made
some beautiful drawings of these remains, which may now
be seen in the Woodwardian Museum at Cambridge. Next
we find our own scientific men, Hooke, the naturalist Ray,
and a famous geologist Dr. Woodward, speculating why the
earth's crust is made up of different layers, one above
another, with different fossils in each. Woodward (1695)
made a careful collection of specimens of chalk, gravel, coal,
marble, and other rocks, together with the fossils which he
found in them ; and these also are in the Cambridge Mu-
seum. But all these men, though they did good work, still
held very erroneous notions about the way in which the
crust of the earth had been formed.

The first geologist who gave any real explanation of the
facts was Lazzaro Moro, an Italian, born at Friuli in Lom-
bardy, in 1687. Moro pointed out, as Woodward had done
before him, that the different strata lie in a certain order one
above the other, and that within them are imprisoned fossil
fishes, shells, corals, and plants, in all countries, and at all
heights above the sea. The rocks, said Moro, writing in
1740, must have been soft when these fossils were buried in
them, and some must have been near rivers, because they con-
tain fresh-water animals and plants j while others contain only
marine fossils, and must have been laid down under the sea.
It is clear, then, that they must all have been formed in lakes
or seas, and have been raised up by earthquakes, or thrown
out by volcanoes, such as we see taking place from time to
time in the world now. This explanation, though rough, was
true, and Moro deserves to be remembered as one of the
first men who led the way towards a true study of the earth.

CH. XXVI. WERNER ON GEOLOGY. 217

After him there followed many others, whom we cannot
mention here; but the next whose name is famous was
the great Werner, professor of mineralogy at Freyberg in
Saxony.

Werner calls Attention to Geology, 1775. — Abraham
Werner, the son of an inspector of mines in Silesia, was
born in 1750. His first playthings were the bright minerals
which his father's workmen gave him, so that he knew them
by sight, even before he could tell their names ; and as he
grew up he seemed to care for nothing but mineralogy and
the wonderful facts it revealed about the formation of the
earth. Freyberg, when he first began to lecture there, in
1775, was only a small school for miners ; but it was not long
before he raised it to the rank of a university, so great was
the fame of his lectures. He pointed out to those who came
to learn of him, that the study of the rocks was something
more than merely searching for minerals ; and that the crust
of the earth was full of wonderful histories, which might be
read by those who cared to take the trouble. He pointed
out how some formations were stratified, that is, arranged in
layers, and contained fossil shells and other organic remains ;
while, on the other hand, some were unstratified, and had
no fossils in them. Some rocks were bent, as in Fig. 35 ;

Fig. 35. . ,

Diagram of Bent Rocks. (Page.)

Others had been snapped asunder and forced one up and
the other down, as in Fig. 36 ; and he bade them try to seek
out the reason of these bendings and breakings of the earth's
crust. He reminded- them also that mining was one of the
11

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great roads to wealth, and that even the history of nations
often depended upon the kind of ground which they had
under their feet. By facts such as these he opened men's
eyes to see the wonders of the earth's crust, so that people
began to talk everywhere of the geological lectures of Werner,
and numbers flocked from distant countries, and even learnt
the German language, that they might come and hear him.

In this way he spread the love of geology all over Eu-
rope. He was so eager and earnest himself that his pupils
could not fail to catch some of his enthusiasm, and to try to
follow out his ideas. But, unfortunately, this very enthu-

Diagram of rocks which have been rent apart at the pointy) and tilted up, i, i, 2, 2,
&c., Beds which before the distuibance were continuous.'

siasm led him to insist upon a theory which kept back his
favourite science for many years.

Neptunists and Vulcanists. — Werner had only studied a
small part of Germany, and there were then very few de-
scriptions of other parts of the world which he could read ;
and so, from want of knowledge, he formed the mistaken
idea that in olden times, after the globe had cooled down
and become fit for living beings, there were no volcanoes
for long ages, but that basalt and other rocks, which we
now know were made by volcanic heat, were all laid down
by water. There were men living in Werner's time who
knew that this was a wrong theory, but he would not listen
to their arguments, and the two parties became so violent
that many years were lost in angry disputes between the

' Kindly drawn for me by Professor Ramsay.

CH. XXVI. BUTTON ON GEOLOGY, 219

Neptunisfs, or those who thought all rocks were laid down
by water, and the Viikanists^ who contended that many rocks,
such as basalt, were made by volcanic heat.

Hutton teaches that it is by the Study of Changes
going on now that we can alone learn the History of the
Fast. — While these discussions were going on upon the
Continent, a Scotchman was setting to work in the right
way to settle the question. This man was Dr. Hutton,
one of the greatest geologists that has ever lived ; and the
reason of his greatness was the same which we have found at
every step in our history of science. Before he made any
theory he sought out the facts. He travelled and observed
for himself, he collected patiently details about the layers or
strata in the formations of all countries through which he
passed \ and it was only after all these investigations that in
1788, when he was sixty years of age, he wrote his famous
' Theory of the Earth,' in which he showed how the history
of the earth's crust might be traced out This work, al-
though very interesting, was not much read ; but one of
Hutton's favourite pupils, the celebrated Dr. Playfair, wrote
a book called ' Illustrations of the Huttonian Theory,' by
means of which Hutton's opinions became well known.

About Hutton himself there is very little to tell. He was
born in Edinburgh in 1726, studied medicine, and took his
doctor's degree in Leyden in 1749, and then returned to
Edinburgh, and devoted all his life to science. Of his
teaching I should like to write a great deal, but we must
content ourselves with a little which you can understand.
His great principle was that it was useless to try and guess
how the rocks had been made and fossils buried in them,
for this had only led to endless confusion and disputes.
Men must go, he said, and see with their own eyes how

220 EIGHTEENTH CENTURY. pt. hi.

rocks are being made now, how rivers and glaciers are
carrying down earth and stones from the mountains into the
sea, and how volcanoes are throwing out melted matter
which cools dowTi into hard rock j and then they must com-
pare these with the older rocks in the crust of the earth, and
see whether they were not formed in the same way.

Aqueous (or water-made) Rocks. — When we find a piece
of marble made up almost entirely of oyster and other shells,
and of pieces of coral, we cannot doubt that it must once "
have been a heap of loose shells and corals such as we now
see on the shore or under the water, and that it has since
been hardened into Hmestone. When we find that by
crushing or scraping sandstone we can turn it into sand
like that which we see on the seashore, and which we know
has been made by the sea grinding the stones and rocks of
the beach against each other, then we cannot doubt that
the sandstone has once been loose sand, and before that was
part of a rock which has been ground down by the waves.

And so we are led to the conclusion that the rocks of
our earth, as we see them now, have been formed out of the
materials of still older rocks which existed before them, and
are being gradually moulded into other and newer rocks,
which will exist when these have been destroyed. Our solid
earth is being wasted every day. The sides of the moun-
tains are washed down and their materials are carried through
the valleys by the running water. In this way the soil is
brought down to the coast, and here it is eaten away by the
waves of the sea, and falls to the bottom of the ocean, out
of which it will be raised again by earthquakes, volcanoes,
and other movements of the earth's crust, such as can be
proved to be going on in parts of the world at this day. As
far back as investigations and reasoning can go we find

CH. XXVI. IGNEOUS ROCKS. 221

everywhere signs that these gradual and incessant changes
have always been going on, and that the face of our earth,
as we now see it, has been moulded out of the ruins of an
older world.

Igneous (or fire-made Eocks). — But how are we to decide
about those rocks, such as basalt, which Werner thought
were made by water? Hutton was convinced they were
formed in volcanoes ; and yet it was true that they did not
contain bubbles of air as lava does, which has poured
down the sides of a volcano in the open air. Here his
friend and pupil Sir James Hall came to his assistance by
melting pieces of rock in his chemical laboratory, and letting
them cool do\^n under very heavy pressure. When this was
done they could hardly be distinguished from pieces of
basalt which he took out of the earth. It is clear, there-
fore, he said, that these rocks have either cooled down in-
side the volcano, with a great weight of rocks above them,
or have been poured out under the sea, which would press
down heavily upon them and shut out the air.

Another question which Hutton cleared up in the same
way was that of the formation of granite. Werner believed
that all the granite rocks, of which you may see plenty in dif-
ferent parts of he world, were made first, before any other
rocks were laid down by water. Hutton did not think this was
true, but that, on the contrary, granite might be even now form-
ing deep dowm within the crust of the earth. But how was
he to prove this ? He said to himself, ' If melted granite
forms under the softer strata which have been laid down
by water, it ought occasionally to obtrude itself into them
in narrow wedges when it is expanded by heat, and I shall
be able somewhere to find veins of granite piercing the
rocks above.'

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EIGHTEENTH CENTURY.

FT. U\,

To prove whether this was so he made a journey to the
Grampians, where there are large masses of granite ; and
there, in Glen Tilt, he found the veins of red granite branch-
ing out into the clay-slate and limestone rocks above, as
in Fig. 37. It is easy in this diagram to see that the
water-made layers, «, b, must have been there before the
granite was melted, otherwise it could not have sent the
straggling veins, c c, up into them. And so he convinced
himself that softie granites are newer than the aqueous rocks
which lie above them. It is said that he was so delighted

Fig. 37.

Granite Veins in Glen Tilt.
a. Clay slate, b. Limestone, c. Granite veins.

at finding this proof that the guides who were with him
thought he had discovered a vein of gold.

This is one out of many examples of the way in which
Hutton worked and corrected the mistakes which had
sprung up in the German school of geology. Werner had
taught his pupils that there was really something to be learnt
from the study of the rocks ; that they could be made to
tell real histories of the past and help men to get wealth for
the future, and thus he persuaded them to give time and
thought to this work. Hutton showed that to carry on this
study rightly they must open their eyes to all that is going

CH. XXVI. WILLIAM SMITH. 223

on now, and that the only way to read the history of the
past is to compare it with the present.

"William Smith surveys the Rocks of England. — Mean-
while another man, whom we must not forget to mention, was
working away very quietly without any help, and with very
little money \ and yet in his way was doing at least as much
work as the others. This was William Smith, a plain Eng-
lish surveyor, who was so much struck with the arrange-
ment of the different formations in the hills among which
he travelled that he determined to try and map them out
so as to show exactly how the strata are placed one above
the other, and what counties they pass through.

He began his work in 1 790, and travelled over the whole
country, chiefly on foot, marking as he went all the different
positions of the rocks, and collecting the shells and other
fossils which he found in them. He had not gone on long
before he observed that certain fossils which appeared in the
lower beds disappeared when he reached those which lay
above them, and that others took their place ; so that in this
way it was possible to use the fossils to trace out the age of
any particular rock, just as the face of a coin helps you to
tell the reign in which it was cast ; and the story told by
the fossils agreed very well with the divisions which he had
worked out by the position of the rocks above each other.
He was even so observant that he distinguished between
the fossils which had their edges fresh, showing that they
had not been disturbed since they were buried in the earth,
and those which were rubbed and water-worn. The fresh
ones only, he said, are of use to tell the age of a rock, for
those which are rubbed may have been washed out of some
older formation by rivers.

In this way William Smith, for pure love of science, and

224 EIGHTEENTH CENTURY, pt. hi.

without any hope of gain, travelled over the whole of Eng-
land and Wales, mapping out the rocks and noticing all
their peculiarities. In 1799 he published a list or tabular
view of the formations with their fossils, and the places
where they might be seen in the hills; and in 18 15 he at
last succeeded in completing a geological map of England,
which has ever since formed the foundation of our British
geology, and which remains a lasting monument of what one
man may accomplish by patience and indefatigable industry.
William Smith fairly earned the title of the ' Father of Eng-
lish Geologists,' which has ever since been given him, and,
with Werner and Hutton, deserves to be remembered as one
of the founders of the science of geology.

Chief Works consulted. — Lyell's 'Principles of Geology;' Lyell's
* Student's Elements of Geology ; ' Page's ' Advanced Text-Book of
Geology ; ' Hutton's ' Theory of the Earth ;' Fitton's 'Notes on Pro-
gress of Geology in England ; ' ' Life of Werner ' — ' Naturalists'
Library,' vol. xxxix.

CH. XXVII. MODERN CHEMISTRY. 225

CHAPTER XXVn.

SCIENCE OF THE EIGHTEENTH CENTURY (CONTINUED).

Birth of Modern Chemistry — Discovery of 'Fixed Air,' or Carbonic
Acid, by Black and Bergmann — Working out of * Chemical
Affinity ' by Bergmann — He tests Mineral Waters, and proves

* Fixed Air ' to be an Acid — Discovery of Hydrogen by Cavendish
- — He Investigates the Composition of Water — Oxygen discovered by
Priestley and Scheele — Priestley's Experiments — He fails to see the
true bearing of his Discovery — His Political Troubles and Death
— Nitrogen described by Dr. Rutherford — Lavoisier lays the
Foundation of Modern Chemistry — He destroys the Theory of

* Phlogiston ' by proving that Combustion and Respiration take up a
Gas out of the Air — Discovers the Composition of Carbonic Acid
and the nature of the Diamond — French School of Chemistry —
Death of Lavoisier.

During the last half of the eighteenth century, while Hunter
and Linn^us were adding to our knowledge of living beings,
and Werner and Hutton were reading the history of the
crust of the earth, a little group of men in England, France,
and Sweden were making discoveries which entirely altered
the science of chemistry. These men were Bergmann and
Scheele in Sweden ; Black, Cavendish, and Priestley in Eng-
land ; and Lavoisier in France.

In order to understand what their discoveries were, and
what they taught us, it is necessary to bear in mind that up
to this time chemists had believed fire, air, and water to be
simple substances which could not be decomposed or split
up into any other kind of matter. Mayow, indeed, had

226 EIGHTEENTH CENTURY. pt. hi.

shown that the atmosphere could be separated into two
gases, but his experiments had been passed over and for-
gotten; and though Dr. Hales, at the beginning of the
eighteenth century, had collected several gases, he had not
distinguished them from air. The fact was that Stahl's
imaginary ' phlogiston,' which was supposed to pass out of
burning and breathing bodies into the air, was a constant
source of confusion, and led men away from the truth.

But the time had now come when these misty ideas were
to be dispelled, by the discovery of the four gases — carbonic
acid, hydrogen, oxygen, and nitrogen.

Discovery of ' Fixed Air,' or Carbonic Acid, by Black,
1756. — The first step was made by a Scotch physician
named Black, who was bom in 1728, and became Professor
of Chemistry at Glasgow in 1756. Here he made many
valuable experiments, and among other things he was very
anxious to find out why limestone altogether changes its
character when it is burnt. If you take a piece of ordinary
limestone or chalk, and put it in water, it will remain
without any change unless you add a little acid to the
water, and then the limestone will effervesce, and bubbles
will begin to rise up from it. But if you take a piece
of the same limestone and burn it in a fire, it turns into
a powder called quick-lime, v/hich will no longer give out
bubbles when you pour acid upon it, but directly you mix
it with water it will swell up and become intensely hot,
as you may see for yourself if you watch bricklayers making
mortar by the roadside. This complete change in the lime-
stone, caused by merely heating it, had been a great problem
to chemists; and Dr. Black was still more puzzled by finding
that the lime was lighter after it had been burnt, although
he could not discover that it had lost anything except a Httle

CH. XXVII.

BLACK'S 'FIXED AIR:

22'/

water, which was not enough to account for the loss of
weight.

At last he remembered that Dr. Hales had driven air out
of substances, and collected it in bottles ; and he began to
consider whether the heat of burning might not have driven
some heavy kind of air out of the limestone, and so made it
lighter. To prove this he made the experiment which has
since been always used for making small quantities of car-
bonic acid gas. He put some pieces of limestone in the
bottle, a. Fig. 38, and poured upon them some water and

Fig. -,8.

Carbonic Acid rising from Limestone and Acidulated Water (Griffin).

a. Bottle containing pieces of limestone in water and acid, b. Connecting tube.

c. Inverted jar, out of which the rising gas is driving the water.

some acid. He then stopped the bottle with a tight cork,
and joined it by the tube ^ to a large glass jar, c, filled with
water, and standing with its open end downwards in a
vessel of water. In a few moments the bubbles began to
rise from the limestone, and passing into the jar, c, drove
out the water and filled the jar with gas.

This gas Black called ' fixed air,' because it had been
fixed in the limestone before it was driven out by the
acid. He collected and weighed it, and found that it exactly

228 EIGHTEENTH CENTURY. pt. hi.

made up the weight which the limestone had lost. He then
reversed the experiment, and taking some water which had
lime dissolved in it, he passed some 'fixed air' into it, and,
as he expected, the gas joined itself to the lime and formed
a powdered white chalk at the bottom of the bottle. By
these two experiments he proved that limestone is composed
of lime and * fixed air.'

He then proceeded to examine the gas itself. He found
that animals died in it, and that a flame would not burn in
it, and also that it was the same gas as that which bubbles
out of beer and other liquids when they ferment, and often
out of mineral springs. He also proved that there is ' fixed
air ' in our breath, by breathing into a glass of lime-water,
and thus forming powdered chalk, which fell to the bottom
of the glass.

All this Black discovered about ' carbonic acid,' which is
sometimes called ' fixed air ' even now, when people speak
of it in efiervescing drinks. He did not know that it is an
acid ; this discovery was made by Bergmann of Sweden, of
whom we must now speak.

Bergmann shows that Fixed Air is an Acid — Works
out 'Chemical Affinity' of many Substances. — Torbern
Bergmann, who was born in 1735 in West Gothland, was
the son of a tax-collector, and he had the greatest difficulty
in getting permission to study science. His father had in-
tended him for the law or the church, and it was not until
his scientific books had been burnt, and he had fallen ill
with disappointment, that they saw it was useless to oppose
him, and he was allowed to take his own course. From
that time he was happy ; he put himself under the great
Linnseus, and in 1761 became Professor of Natural Philo-
sophy at Upsala, and afterwards of Chemistry at Stockholm.

CH. xxvii. CHEMICAL AFFINITY. 229

Bergmann made a great advance in chemistry by working
out the ' che7nical affinity ' of many substances, and showing
how to make use of it to test or try mineral waters.

Nearly a hundred years before Bergmann began to study
chemistry, Newton, when writing on attraction, had pointed
out that when substances are mixed together some kinds
attract each other very strongly and join together, making
one compound substance. For instance, he said, if you
put copper into nitric acid the copper will dissolve and dis-
appear ; but if you plunge a piece of iron into the liquid the
copper will re-appear and fall to the bottom of the glass,
because the iron attracts the nitric acid more strongly than
the copper does, and so it takes it up out of the liquid,
setting the copper free.

Chemists had till now neglected this observation of
Newton's, but Bergmann followed it out, and by a number
of experiments he made out a table of those substances
which seemed to have the greatest affinity for each other,
and which would unite whenever the conditions would allow
them. This he called a table of ' elective affinities.^

It is easy to see how this could be used for testing or
trying what substances lie hidden in mineral waters. Iron,
for instance, in the case given by Newton, would show when
copper was dissolved in a liquid containing nitric acid.
Boyle, too, had shown that a blue liquid extracted from the
lichen called lit^nus turns to a bright red directly it touches
an acid j so that blue litmus is a sure test of an acid. Again,
common salt put into a clear liquid containing silver, turns
it cloudy ; while tincture of gall-nuts makes a purple cloud
in a solution containing iron. Bergmann worked out a
number of these tests^ and by means of them analysed or
separated out the substances contained in mineral waters ;

230 EIGHTEENTH CENTURY. PT. ni.

he even melted solid minerals in acids and tested them in
the same way.

One of the first uses that he made oif his tests was to try-
Black's 'fixed air.' When he heard of this gas he suspected
that it must be an acid, because it Joined itself to lime,
which is an alkali, that is, a substance in all respects unlike
an acid ; and he had found that unlike substances nearly
always attract each other most strongly. So he made
some ' fixed air ' and tested it with blue litmus, and, as the
litmus turned red directly, he knew that he was right in
supposing it to be an acid, and he called it ' aerial acid,' or
acid air. He then weighed it and proved that it was heavier
than common air, and bypassing it through water he showed
that a large quantity of it would dissolve.

Thus these two men, Black and Bergmann, had arrived
at a pretty good knowledge of this gas. They had proved
that it is an invisible heavy kind of air ; that it dissolves in
water ; that it is acid and joins itself to lime, forming Hme-
stone or chalk ; that it destroys life when breathed, and
puts out a flame ; that it is given out by fermenting liquids,
and from mineral springs, and is contained in our breath.
One thing they had not found out, namely, that it is made
up of two elements ; this, as you will see (p. 238), was dis-
covered by Lavoisier in 1779, when he gave it the name of
* carbonic acid.'

Discovery of Hydrogen by Cavendish, 1766. — The next
gas discovered was hydrogen, and its discoverer was Henry
Cavendish, grandson of the Duke of Devonshire, who was
bom in 1731. Cavendish was a very shy and reserved man,
who lived much alone and found his greatest pleasure in
studying science for its own sake. It is even related of him
that he taught all his servants to understand by signs what

CH. XXVII. HYDROGEN AND OXYGEN. 231

he wanted in order that he might be able to think without
interruption.

In the year 1766 he read a paper before the Royal

Society upon a gas which he called ' inflammable air/

because it burst into a flame whenever a light was brought

near it, and also because he believed it to be the cause of

the explosions which so often take place in mines. He

obtained this gas by pouring sulphuric acid and water upon

zinc, iron, or tin, and then collecting the bubbles as Black

had done (see Fig. 38, p. 227). But when he began to make

experiments with this gas he found it very different from

Black's ' fixed air.' It is true that a candle would not burn,

nor could animals breathe in it ; but when a light was brought

near it, it took fire and burnt with a pale blue flame inside

the bottle. Then instead of being heavy like ' fixed air,' it was

lighter than the atmosphere, and for this reason it was soon

used for filling balloons. It had also another remarkable

peculiarity, that when mixed with air in a bottle, it exploded

with a loud noise directly a light was brought near it, leaving

drops of moisture inside the bottle. Cavendish did not

understand the cause of this explosion at first, but in^ 1784

(after Priestley had discovered oxygen) he mixed pure oxygen

and hydrogen in a closed vessel, and lighted them by an

electric spark, and then he made the great discovery that

these two gases, when lighted, rush together and form zvater,

which is therefore a compound substance made of oxygen

and hydrogen.

Oxygen discovered by Priestley in 1774, and by Scheele
in 1775. — The next gas discovered was oxygen, the most
common and the most useful of all the substances in our
globe. It was discovered independently by two men —
Priestley, a dissenting minister at Leeds, and Scheele (born

232 EIGHTEENTH CENTURY. pt. hi.

1742), a small apothecary at Kj5ping, a little village in
Sweden.

There is no doubt that Scheele deserves as much credit
for this discovery as if Priestley had never made it, for he had
not heard of his experiments, and he added many useful
facts which Priestley did not know. Still, as they both went
over much the same ground, we cannot afford space here to
give Scheele's experiments. You must not, however, forget
his claim, for though the world often forgot him because he
remained a poor apothecary all his life, yet Scheele was
really one of the first chemists of Europe. We owe to him
the discovery of chlorine ; and of manganese, barytes, fluor-
spar, and many other earths whose names I cannot expect
you to know. Indeed, his merit was so great that Bergmann,
his friend and patron, once said, ' The greatest discovery he
ever made was when he discovered Scheele.'

Joseph Priestley, the discoverer of oxygen, was born in
1733- The greater part of his life was spent in writing upon
religious subjects, and it was only in his leisure hours that
he studied chemistry. He tells us in his autobiography that
he first began to take an interest in such things in conse-
quence of visiting a brewery next door to his house and
watching the fixed air which rose from the beer-vats. His
first chemical experiment of any value was to force this ' fixed
air ' into pure water^ thus making an effervescing drink much
the same as the soda-water we drink now. He next tried
what effect growing plants have upon air, and by keeping a
pot of mint under a bell-jar in which the air had been spoilt
by burning or breathing, he proved that plants take up the
bad air and render the remainder fit again to support a
flame or life. He did not, however, yet know why this took
place. He also invented a number of troughs and other

CH. XXVII.

PRIESTLEY'S DISCOVERIES.

233

apparatus for collecting and washing gases, and amused
himself as Hales had done in driving gas out of different
substances.

And thus it happened that one day, August 1, 1774, he
made an experiment which led to a great discovery. He
took a red powder called mercuric oxide^ which he knew
contained mercury and something else besides, and he put
it into the bulb, a^ Fig. 39 ; the rest of the tube he filled

Fig. 39.

Priestley's Apparatus for procuring Oxygen.

a. Bulb containing red mercuric oxide, h, Vessel containing mercury, c. Inverted
jar for collecting the gas. d, Burning glass.

with mercury, and passed it into the basin b, and up
into the jar r, both h and c being also filled with mercury.
He next took a powerful burning-glass, d^ and brought the
rays of the sun to a focus upon the red powder. As soon
as the powder became very hot a gas rose out of it and
passed along the tube into the jar, <:, driving out the mer-
cury j while the red colour began to disappear in the bulb,
a, and only pure shining mercury remained behind. So far
he ?iad only proved that red mercuric oxide is made up of
mercury and a gas.

When he had collected enough gas to experiment upon,

234 EIGHTEENTH CENTURY. pt. hi.

he passed some of it through water and found that it did not
dissolve as ' fixed air ' does j but what surprised him still
more was that a candle put into it burnt with a large
vigorous flame, and a piece of red-hot charcoal burst into
flame in it and burnt furiously. It was clear then that this
could not be either ' fixed air ' or ' inflammable air/ for
neither of these would feed a flame. He next put two mice
into some of the gas, and he found that they lived much
longer than in ordinary air. When he breathed it also into
his own chest he felt singularly light and easy for some time
afterwards. * Who can tell,' he writes, * whether this pure
air may not at last become a fashionable luxury? As yet
only two' mice and myself have had the privilege of breathing
it.'

Here, you see, we have come back again to Mayow's
fire-air, so long forgotten, which supports life and flame.
Priestley had learnt more about it than Mayow had, for he
had collected it separately, had burnt it, and breathed it with-
out other air being mixed with it ; and he had moreover
shown that it could be driven out of metallic compounds,
for mercury is a metal. Yet it is disappointing to learn that,
in spite of having gone thus far, Priestley was so imbued
with'Stahl's theory of 'phlogiston,' that he did not really
understand the great discovery he had made, but called his
gas * dephlogisticated air,' or air which had lost that
imaginary ' phlogiston ' which was always confusing men's
minds.

There is no doubt that he discovered the gas and showed
that it was the chief actor in combustion and respiration,
and for this discovery and that of an immense number of
other gases, he was elected a member both of the Royal
Society and the Academic des Sciences, and his fame was

CH. XXVII. NITROGEN. 235

great all over Europe ; yet still he had not hit upon the
entire truth — he had given the facts, and it remained for
Lavoisier to read the riddle.

Besides his chemical writings, Priestley published many
books on theology, and though he was a singularly gentle
quiet man, yet his religious and political essays were often
very severe, and they led to his being driven out of Bir-
mingham, and his house burnt by the mob, when they at-
tacked the leading Dissenters during the panic caused by
the French Revolution. After living for some time near
London he emigrated to America, where he died in 1804.
He continued his chemical experiments up to the time of
his death, and made many important discoveries, but the
chief discovery which will always be connected with his
name was that oi oxygen, in 1774.

Properties of Nitrogen determined by Dr. Rutherford
in 1772. — There now remains to be mentioned only one of
the four gases spoken of at page 226, namely, nitrogen.
This gas was first properly described by Dr. Rutherford in
1772, but there is very little to be said of it except that it
has scarcely any of those properties which belong to the
other gases. It does not support life or flame like oxygen ;
it does not make lime-water cloudy as carbonic acid does,
nor does it burn like hydrogen. In fact, it is a dull sleepy
gas, which remains after oxygen has been taken out of the
air, and which can be driven out of many solid bodies,
especially nitre or saltpetre.

Lavoisier lays the Foundation of Modern Chemistry,
1778. — The determination of nitrogen completes the history
of the discovery of those gases of which fire, air, and water
are composed ; but you will have noticed that we have not
yet arrived at the new explanation of chemical changes which

236 EIGHTEENTH CENTURY. pt. iir.

was to take the place of * phlogiston.' The fact is that
Black, Bergmann, Cavendish, Scheele, and Priestley, were all
so cramped by the old theory, that though they discovered
the facts they could not make the right use of them. The
man who did this, and who laid the foundation of modern
chemistry, was the celebrated French chemist, Lavoisier.

Antoine Laurent Lavoisier was bom in Paris in 1743.
His father, who was a wealthy merchant, gave him a
splendid education, and when he was still quite young the
new discoveries which were being made in chemistry tempted
him to learn that science. At twenty-one years of age he
received a gold medal from the Academie des Sciences for
a very elaborate and learned essay on the best way of light-
ing the streets of Paris. At five-and-twenty he was elected
a member of the Academie, and from that time he deter-
mined to devote his life to chemistry.

As early as 1770 Lavoisier had begun to suspect that
the famous theory of phlogiston was false. His chief reason
for thinking this was that he found, as Geber had done more
than 900 years before (see p. 44), that when metals are
heated so that they turn into powder, the powder weighs
more than the original metal did before it was heated.
Moreover, he also found that the air which remained behind
in the vessel in which the metal had been heated had lost
exactly as much weight as the metal had gained. So it seemed
to him clear that the metal must have taken something y9'^w.
the air instead of giving anything to it.

For eight years Lavoisier worked incessantly at this
problem. He heated many metals, such as iron, lead, tin,
&c., and other substances such as sulphur and phosphorus,
and in every case, if he collected all that remained, he found
it heavier than before. But there was one point in which he

CH. XXVII.

LA VOISIER'S EXPERIMENTS.

237

could not succeed j he could not make the metals give back
again what they had taken from the air, so that he might
examine it. At last, in 1778, it occurred to him that
Priestley had separated mercuric oxide into two substances ;
namely, the metal mercury and a gas. Here, then, was just
the step he wanted. If he could first make mercuric oxide
by heating mercury in the air, and then afterwards separate
it back again into mercury and a gas, he would thus prove
what it had taken out of the air. He therefore took some
mercury and put it into a tube a, Fig. 40, which was connected

Fig. 40.

Lavoisier's Apparatus for Heating Mercury and making it take up Oxygen.

A, Bulb containing mercury. B, Vessel containing mercury, c. Bell-jar partly full

of air. D, Stove.

with a bell- jar c, containing air and standing over mercury.
Then he heated the bulb a over the stove d, and kept the
mercury boiling for twelve days.

During the first five days little by little red specks began
to appear on the top of the mercury in c, that is, mercuric
oxide was formed ; but after that time, when about one-fifth
of the air in the bell-jar, c, had disappeared and mercury
risen in its place, no further change took place. He then
lifted off the bell-jar and took 45 grains of this red powder
and made Priestley's experiment with it (see p. 233),

238 EIGHTEENTH CENTURY. pt. hi.

and he obtained, of course, the gas which Priestley had
called * dephlogisticated air.' He afterwards found by more
exact experiments that the amount of this gas contained in
the mercuric oxide exactly equalled the amount lost by the
air in which the mercury had been heated.

Now see what Lavoisier had done : he had proved that
the reason why air shrinks when substances are burnt in it,
is because the substances take up a gas out of the air, and he
had also shown that this gas is the same as that which
Priestley discovered. Now, at last, the false theory was
destroyed, and the starting-point of a true theory was found.
The imaginary phlogiston, which had been supposed to load
the air when anything was burnt in it, was proved never to
have had any existence; for it was clear that just the
opposite effect takes place. All burning and breathing afid
the change in metals is caused by a gas being taken up out
of the air and joined to other substances. Lavoisier called
this gas oxygen (from o^vc, acid ; ytwaM, I produce), because
he found that most substances were acid after they had
been united with it. This, too, led him to suspect that as
' fixed air ' was an acid, and could be made by burning char-
coal, it must be composed of oxygen and carbon. So he
burnt small quantities of charcoal in pure oxygen, and by
analysing the 'fixed air' produced proved that 100 parts by
weight of this gas contained 72 parts of oxygen and 28 of
carbon. For this reason he called it 'carbonic acid,' a
name which it still bears. By burning a diamond in oxygen
and producing carbonic acid, he also proved that a diamond
is pure carbon.

Lavoisier had very great difficulty in persuading the
other leading chemists that they had been labouring under a
false idea, and that substances when burning do not put

CH. XXVII. RAPID ADVANCE OF CHEMISTRY. 239

something into the atmosphere but take a gas out of it. Dr.
Black was one of the first to be convinced, but Priestley
died without giving up his old opinions. The younger
chemists, however, saw the truth of Lavoisier's explanation,
and from this time chemistry advanced very rapidly.
Lavoisier invented an entirely new set of terms instead of
the old names of the alchemists, and though his terms have
been greatly altered by later discoveries, still many of them
will always be used. He repeated with a better apparatus
Cavendish's experiment of turning hydrogen and oxygen
into water, and he gave hyd^vgen its name from vlwp^ water,
and yEvvao), I produce. Lastly, he published his * Elements
of Chemistry,' in which he gave a clear explanation of the
different chemical changes, and how students could work
them out for themselves.

Lavoisier was now at the height of his fame, full of his
new theory, and prepared to devote the rest of his life to
making chemistry a grand science ; but a very sad fate was
awaiting him. In 1793 the great French Revolution broke
out in Paris. Lavoisier was a farmer-general, that is a kind
of collector of taxes, and all the farmers-general were hated
by the people ; so he knew that he should most likely lose
all his fortune, and was prepared to work for his living ; but
he had not expected the blow which fell upon him. All the
farmers-general were condemned to death, and though a
physician named Halle, who deserves always to be remem-
bered for this act, pleaded that Lavoisier's life should be
spared till he had completed his experiments, the ignorant
and brutal Government replied, ' We do not need learned
men,' and on May 18, 1794, at the age of fifty-one, Lavoisier
was guillotined.

After his death the French School of Chemistry took the

240 EIGHTEENTH CENTURY. pt. hi.

lead for many years, until new discoveries in England, which
we shall mention by-and-by, made another great advance.
When you are able to read larger works upon the history of
chemistry you will find how very interesting the period was
of which we have been speaking. I have only been able to
give you here the very barest outline of it, so that the names
of these great chemists may not be quite unfamiliar when
you meet with them in other books.

Chief Works consulted. — 'Three Papers on Factitious Air,' by
Cavendish — 'Phil. Trans.,' 1766; Brande's 'Chemistry;' Hoefer's
* Histoire de la Chimie ; ' Cuvier, ' Histoire des Sciences Naturelles ; '
Huxley, 'On Priestley' — 'Macmillan's Magazine,' 1874; Priestley, *0n
Different Kinds of Air,' 1774 ; Thomson's ' Hist, of Royal Society ; '
Scheele's ' Chemical Experiments on Air and Fire,' translated 1 780 ;
Miller's ' Elements of Chemistry ; ' Lavoisier's ' Elements of Chemis-
tr}',' translated by Kerr, 1790.

CH. xxviii. DR. BLACK. 24.1

CHAPTER XXVIII.

SCIENCE OF THE EIGHTEENTH CENTURY (CONTINUED).

Doctrine of Latent Heat, taught by Dr. Black in 1 760 — Water con-
taining Ice remains always at 0° C, and Boiling Water at 100° C,
however much Heat is added — Black showed that the lost Heat is
absorbed in altering the condition of the Water — Watt's Applica-
tion of the Theory of Latent Heat to the Steam-engine — Early His-
tory of Steam-engines — Newcomen's Engine — Watt invents the
Separate Condenser — Diagram of Watt's Engine — Difficulties of
Watt and Boulton in introducing Steam-engines.

Discovery of Latent Heat by Dr. Black in 1760. — ^We

must now go back a few years, to the time when Dr. Black
was lecturing at Glasgow in 1760; for he then made a
remarkable discovery about heat, which belongs to the
history of physics rather than of chemistry. This was
the discovery of latent heat, or of heat which becomes lost
or hidden whenever ice is turned into water, or water into
steam.

If you put a lump of ice in a saucepan on a stove, and
when it begins to melt stir it gently so as to keep the water
well mixed, you will find that so long as the smallest piece of
ice is left in the water, a thermometer standing in the sauce-
pan will not rise higher than 0° Centigrade, or the melting-
point of ice. Now the heat from the stove must be con-
tinually entering the water, otherwise the ice would not melt.
What then becomes of this heat ?• Again, if you keep the
water on the stove after the ice is melted, it will grow hotter
12

242 ' EIGHTEENTH CENTURY. PT. III.

and hotter till it reaches ioo° Centigrade, when it will boil.
Here, again, it will remain at the same temperature, and
though you go on boiling it till it has all passed away in steam,
the last drop of water will never be hotter than ioo° C. So
that here again the heat which is added remains hidden
and does not become apparent. This last fact about boiHng
water had been long known to philosophers, but no one found
any explanation of it until Black began his experiments on
melting ice j and he then came to the conclusion that the
heat is employed in altering the condition of the water,
hat is, in changing it, in the one case from solid ice into
water, and in the other from water into a vapour.

He proved this by some simple experiments which are
not difficult to make. He took two glass flasks, and filled
one with ice just on the point of melting, and the other with
an equal weight of ice-cold water. These he hung in a
moderately warm room, which he kept all the time at the
same heat (8° -5 C). At the end of half an hour the ice-
cold water had risen four degrees (from 0° to 4°), but the
melting ice remained at 0°, and it was ten hours and a half
before the ice had disappeared and the water had reached
the same temperature as that which tlie water in the other
basin had attained in half an hour. Now the melting ice
had been receiving heat for twenty-one half-hours, and
therefore had taken in 2 1 x 4, or 84° of heat, while it only
showed a rise of 4°. It was clear, therefore, that the re-
maining 80° must have been spent in turning the ice into
water.

Black now tried the same thing in another way. He
found that a pound of water at 79° C. would, exactly melt a
pound of ice. So he again took two vessels, in one of which
he put a pound of ice-cold water at 0° and a pound of hot

CH. XXVIII. LATENT HEAT, 243

water at 79°, and when they were properly mixed he found,
as he expected, that the heat of the mixture was half-way
between the two, that is 39^°. In the other vessel he put a
pound of ice at 0° and a pound of hot water at 79°, and
here, when the ice had disappeared, the mixture still re-
mained at 0°, showing that the whole 79° of heat in the
boiling water had been absorbed in melting the ice, and
remained hidden or latent in the two pounds of water. The
latent heat of water is therefore between 79° and 80°.

We know now what becomes of this heat, as you will see
(chapter xxxiv.) in the history of the science of the nine-
teenth century ; but the first step was to prove its disappear-
ance into the water, and this we ow^e to Black ; as well as the
fact that still more heat is lost in turning water into steam.

This last fact he proved by filling a glass bottle half full
of water, corking it very tightly, and then heating the bottle
till the water began to boil. He was obliged to do this very
gently, because steam expands with great power, and he did
not wish to drive out the cork or break his bottle. After a
little time the water ceased boiling, because the other half
of the bottle was full of steam, and there was no room for
more to form. But now the water began to grow hotter
and hotter, and rose above 100° C, showing that when the
heat could no longer form steam it did not remain hidden,
but increased the temperature of the water. At last, when
he was afraid to heat the bottle any more, he loosened the
cork, which flew out with great violence, followed by a cloud
of steam. And now notice what happened ; directly the
rush of steam was over, the heat of the water in the bottle
fell again to 100° C, for- all the rest of the heat had been
used in foi'ming more steam the moment the pressure was
removed.

244 EIGHTEENTH CENTURY. rx. in.

James "Watt, 1736-1819. — Black had now completed
his discovery, and from that time he taught in all his
lectures that heat becomes latent or absorbed when a solid
is changed into a liquid, or a liquid into vapour. It was
about this time that the famous engineer, James Watt, began
to study the power of steam, and as Black was his friend,
he came to him to help him solve his difficulties. The his-
tory of the steam-engine, being the history of an invention,
does not strictly belong to our work ; but the use which
Watt made of the discoveries about steam is a part of
science, and we must therefore find room for a slight sketch
of it here.

James Watt was born at Greenock in 1736 ; he was the
son of a builder and shipwright, and was so delicate as a
child that he was kept at home, and learnt reading from his
mother, and writing and arithmetic from his father. When
at last he was sent to school he found it hard work, for he
was slow and thoughtful, and the other children jeered at
him for his want of quickness. Everyone knows the story
of his being scolded by his aunt for sitting silent a whole
hour, holding first a spoon and then a saucer over the steam
rising from a kettle, and watching drops of water gathering
upon them. It was in this quiet way that little James's
mind grew, and it may be an encouragement to slow, plod-
ding boys to know that one of our greatest inventors was
considered a dull and backward child.

As he grew older James went up to London, and there,
after overcoming many obstacles, which the guilds, or trades'
unions of those days, put in the way of all independent
workers, he learnt to make mathematical instruments, and
then returned to Glasgow, where he began business. Though
he was only one-and-twenty he soon became known as .a

cii. XXVIII. JAMES WATT. 245

man of unusual ability, for the mind of the dull boy had
developed, and his thoughtfulness had begun to produce
results. Not only the students, but even the professors of
the University used to stroll into his little shop to discuss the
discoveries of the day. ' Whenever any difficulty arrested
us,' writes a student named Robison, ' we used to run to our
workman, and he never let go his hold until he had entirely
cleared up the proposed question.' One day it was neces-
sary to read a German book on mechanics ; Watt imme-
diately set to work and learnt German, and another time,
for the same reason, he studied the Italian language. It is
scarcely surprising that a man with such talent and perse-
verance as this, who was also gentle and loving to every-
body, should be sought after both by masters and students.

Among those who came to Watt's shop was one Ander-
son, professor of physics, who, finding that a little model of
a steam-engine in the University museum was out of order,
brought it to Watt to be repaired, and thus led the way to
his invention. And here it is necessary to point out two
things : First, you must not suppose that by a steam-engine
is meant a railway engine ; all contrivances which move by
the power of steam are steam-engines, and locomotive engines
which draw carriages were not made till 1804, long after Watt's
time. Secondly, you must get rid of the idea, which many
people have, that Watt was the first man to make an engine
which moved by steam. This was done long before his time.
The thing which Watt really did was to make an engine such
as we now use, working entirely by steam, without the help
of air, and doing an enormously greater amount of work with
the same quantity of fuel than any others had done before.

The Newcomen Engine, 1705. — Steam had been used
to turn a globe by Hero of Alexandria, a Greek who lived

246 EIGHTEENTH CENTURY. pt. hi.

1 20 years before Christ ; and Baptiste Porta in 1580, Solo-
mon de Cans in 1615, and the Marquis of Worcester in
1663, all tried to make use of steam to do work. Again, in
1690 and 1698, a Frenchman named Papin and an English-
man, Captain Savery, tried to make steam-engines to raise
water out of mines. But the only one of all these engines
which we need describe here was that which fell into the
hands of Watt, and which was made by a man named New-
comen in 1705. A plan of Newcomen's engine is given in
Fig. 41. Its working depended on the pressure of the
atmosphere (explained p. 123) on the piston at one end of
the beam, and the weight of the lump of iron, e^ at the other
end.

The lever-beam of this engine is balanced in such a
way that when it is not at work the weight e pulls it down
on the side away from the engine, and the piston,/,/, is drawn
up to the top of the cylinder, as in the figure. To set the
engine going a fire is lighted under the boiler, and the
tap or stopcock, a, is opened, so that the steam rises into
the cylinder, driving out the air through the air- vent, c. As
soon as the cylinder is full of steam, a is turned off, and the
stopcock, b, turned on. Immediately a small jet of cold
water from the tank t rushes through b into the cylinder,
turning the steam back into a few drops of water, which flow
out with the cold water down the pipe d. Now notice, the
cylinder is quite empty ; for the steam drove out the air, and
the cold water carried the steam away with it, while no air can
come in at c or d, because the little valves in them are kept
shut by the weight of the atmosphere outside. So there is
nothing to hold up the piston, which is being heavily pressed
down by the air above it. The consequence is, down it
comes to the bottom of the cylinder, dragging with it the

CH. XXVIII.

NEWCOMEN'S ENGINE.

247

end of the lever-beam. Directly it reaches the bottom
the stopcock b has to be shut, and a opened again. Up
rises the steam directly from the boiler, driving up the piston,
and the whole thing begins again. In this way the lever-
beam is kept moving up and down by simply turning the

Fig. 41.

Newcomen Engine (Black).

a. Stopcock between boiler and cylinder. 3, Stopcock between cold-water tank and
cylinder, c. Valve closing air-vent, d. Valve closing the outlet for condensed
steam, e. Weight which drags down the beam. /, p. Piston which is pressed
down by the atmosphere when the cylinder is empty.'

two stopcocks one after the other. These were at first
opened and shut by boys ; but one day an ingenious lad
named Humphrey Potter, who wanted to save himself the
trouble of turning the cocks, found that by tying strings from

* The boiler and cold-water tank both in this figure and in fig. 43
are draAvn much too small in proportion, in order to bring them into
the figure.

248 EIGHTEENTH CENTURY. ft. hi.

the handles to the different ends of the beam he could make
the engine open its own cocks as the beam went up and
down. This rough arrangement was soon improved, and
the machine worked by itself.

Watt's Separate Condenser. — Such was the engine as
Watt found it. When he began to examine it he saw at
once what an immense quantity of heat was wasted. Every
time the piston came down, the cylinder, as well as the
steam in it, had to be cooled down j every time the piston
rose, the cylinder had to be heated again ; and the thing
which puzzled him most about it was, that it took six pounds
of cold water to condense only one pound of steam.

It was in this difficulty that he came to Dr. Black, and
learnt from him the theory of latent heafy which showed that
there is an immense store of heat hidden in steam, which
has to be drawn out before it can become water. This was
an entirely new light to Watt, and it led him to make many
experiments still more exact than those of Dr. Black, which
convinced him that no engine would ever work well or
economically, while so much power was wasted in cooling
and re-heating the cylinder at every stroke. But how was
he to cool down the steam without cooling the cylinder
which held it ?

For months he pondered over this without finding any
answer. At last, one Sunday afternoon, when he was walk-
ing on the Green of Glasgow, the way to do it flashed upon
his mind. If he could draw the steam off into a separate vessel
and condense it there, the cylinder might still be kept hot, a7id
the thing would he done. Fig. 42 will help you to understand
how this could be effected. Here the two flasks, a and
B, are first quite emptied of air, and b is half filled with
water. Under b is placed a lamp, d ; under a, a basin of

CH. XXVIII. CONDENSATION OF STEAM. 249

ice, E. Now as long as the tap, c, is kept open, the steam
which is constantly rising from the water in b will rush along
the tube into the empty flask, a, and will there be turned into
drops of water by the cold of the ice underneath, and this
will go on as long as there is any water left in b, because
there will always be an empty space or vacuum in a to re-
ceive the steam as it rises. When the tap, c, is shut, the
steam in b will become very dense, and when it is opened

Fig. 42.

Steam condensed in a separate Vessel.

A, Flask empty of air. B, Flask half-full of water and empty of air. c, Tap con-
necting the two bottles. D, Spirit lamp keeping the water in B boiling, e. Basin
of ice cooling down the steam which passes into A.

again the greater part of the steam will rush out and be
cooled down in a, while b remains hot as before.

Watt's Engine. — This was exactly the plan Watt adopted
in his steam-engine ; b answers to his cylinder (Fig. 43),
which could be kept always hot, and a to his condenser, in
which his steam was turned back into water. We cannot
follow out all the different steps of his invention, and must
content ourselves with a rough description of his engine
after he had completed it, as shown in Fig. 43.

In the first place you must notice that cold water is kept
flowing down from the tank a into b, and out through the pipe
C, so that the condenser standing inside b is kept quite cold :

250

EIGHTEENTH CENTURY.

FT. III.

and, secondly, I must tell you that the rods, i and 2, are so
placed that when the engine-end of the lever-beam is raised,
as in the figure, the stopcocks a and c are open, and b and d
are shut ; and when that end of the beam falls, b and d will be
open, and a and c will be shut.

Let us now begin with the machine as we see it in the
figure. In this position of the beam the cocks a and c are
open j therefore, the steam below the piston will rush out at

Fig. 43.

A

COLD WATER

A, B, Cold water tanks. _ c, Outlet for cold water, d, e, Pumps for drawing off hot
water and sending it along s, s, back to the boiler, p. Tight-fitting piston.
a, d, Cocks for letting steam into the cylinder, b, c. Cocks for letting steam out
of the cylinder, e, e, Pipe which carries steam from boiler to cylinder, o, o. Pipe
which carries steam from cylinder to condenser, i, 2, Rods connecting the cocks
with the lever-beam.

c into the condenser, there to be turned into drops of water,
while the steam from the boiler, entering at «, will force the

CH. XXVIII. WATT'S ENGINE. ■ 251

piston down. But now, the piston having pulled doA\Ti the
beam, a and c will be closed and the other two cocks, b and
d, will be opened. So the steam above the piston will rush
out at b into the condenser, while the steam from the boiler
will pass directly from e down to d, and coming in below the
piston, will drive it up again. In this way, although the cylin-
der is never cooled, the piston moves steadily up and down ;
because the steam is driven off into the condenser standing
in B, where it is turned into water, and is drawn up by the
two pumps D and e, and sent along the pipe, s, s, back to the
boiler.

This was the principle of Watt's double-acting steam-
engine, and if you understand the difference between Figs.
41 and 43 you will see that, though Watt was not the first to
make engines move by steam, he was the first to make a
pure sfeatn-engme, where the piston moves up and down
without any help from the outside air, or of the counter-
balancing weight e, Fig. 41, and without the enormous waste
of heat and fuel which made all the earlier engines com-
paratively useless.

I have only told you here of the way in which he applied
steam to his engines ; all the numberless other improvements
which he made you must read about in books on engineering.
For twenty long years he went on improving and inventing
without reaping any reward for his labour. Other men tried
to steal his ideas and to make a profit out of his genius, and
he had to fight against prejudice and injustice, and against
constant depression caused by his own ill-health. Yet he
found many kind friends upon his road, and amongst the
most famous of these was Boulton, the Birmingham manu-
facturer, who became his partner in 1769, and stood by him
manfully in all his difficulties and troubles. It was from

252 EIGHTEENTH CENTURY, pt. hi.

Boulton's manufactory at Soho (a suburb of Birmingham)
that Watt's engines went forth to the world, and worked that
great change in the manufactures of England which has
made us one of the first nations of the world.

The names of Boulton and Watt deserve to be classed
together as benefactors of mankind. Watt was the inventor,
the man who loved science, and who could not live without
creating. Boulton was the large-minded, enterprising man
of business j he gave Watt men, money, courage, and sup-
port to carry out his inventions \ and by his sympathy with,
and command over the workmen, he led the army which
conquered indifference, persecution, and difficulties, and
established steam machinery in all the workshops of the
world. Watt died in 1819, in the eighty-third year of his
age, and was buried in Handsworth Church, near his friend
and partner Boulton, who had died ten years before.

Chief Works consulted. — Black's 'Elements of Chemistry,' 1803;
'Edinburgh Review,' vol. xiii. 'History of Steam-engines;' Arago,
'Biographies of Scientific Men,' 1857 ; Smiles's 'Lives of Boulton and
Watt ; ' Everett Deschanel's ' Natural Philosophy ; ' Tyndall's ' Natural
Philosophy ; ' Balfour Stewart's ' Treatise on Heat j ' Beckman's ' His-
tory of Inventions.*

CH. XXIX. BENJAMIN FRANKLIN. 253

CHAPTER XXIX.

SCIENCE OF THE EIGHTEENTH CENTURY (CONTINUED).

Benjamin Franklin, bom 1706 — His Early Life— Du Faye discovers
two kinds of Electricity — Franklin proves that Electricity exists in
all bodies, and is only developed by Friction — Positive and Nega-
tive Electricity — Franklin draws down Electricity from the Sky
— Invents Lightning-conductors — Discovery of Animal Electricity
by Galvani — Controversy between Galvani and Volta — Volta
proves that Electricity can be produced by the Contact of two
Metals— Electrical Batteries— The Crown of Cups— The Voltaic
Pile.

Benjamin Franklin, born 1706.-— He Investigates the
Nature of Electricity, 1746. — Benjamin Franklin, the printer
and man of science, was born at Boston, in America, in the
year 1706. He was the son of a tallow-chandler, and had
so many hard struggles in his early life that he does not seem
to have turned his thoughts to science till he was nearly
forty years of age. His father intended him for the Church,
but there was not enough money to pay for his education, so
he was apprenticed to his brother, who was a printer. Here
he worked very hard, yet he used to snatch every spare
moment to read any books which came within his reach ;
but his brother being unkind and harsh to him. a quarrel
sprang up between them, and Benjamin at last ran away to
New York, and from there to Philadelphia. In this last
place he got a little work, but hoping to do better in
England he came to London, where he learnt many of the

254 EIGHTEENTH CENTURY, pt. ill

newest improvements in printing. After a time he went
back to Philadelphia, and from that time he began to succeed
as a printer and became a well-known and respected man.

It was in the year 1746 that he first began to pay atten-
tion to the experiments in electricity which were being made
in England and France. A great deal had been learnt
about this science since the time when Otto Guericke made
the first electrical machine in 1600, and a Frenchman named
Du Faye had shown that two different kinds of electricity
could be produced by rubbing different substances. You will
remember that a pith-ball, when filled with electricity from
a stick of electrified sealing-wax, draws back, and will not
approach the sealing-wax again (seep. 124). But Du Faye
discovered that if you rub the end of a glass rod with silk,
and bring it near to this ball, it will draw the ball towards
itself, showing that the electricity in the glass rod has
exactly the opposite effect to that in the sealing-wax. In
other words, while Guericke had shown that substances
filled with the saine kind of electricity repel each other, Du
Faye showed that substances filled with diffe7'ent kinds of
electricity attract each other. Both these men thought that
electricity was a fluid which was created by the rubbing, and
which was not in bodies at other times ; when Franklin, how-
ever, began to make his experiments he saw clearly that this
was not as they had supposed, but that all bodies have more
or less electricity in them, which the rubbing only brings out.

The way in which he proved this is very interesting ;
but to understand it you must first know that any body
which is to be filled with electricity requires to be so placed
that the electricity cannot pass away from it into the earth.
The best way to do this is to stand it upon. a stool with glass
legs, because electricity does not pass easily along glass.

CH. XXIX. EXPERIMENTS IN ELECTRICITY. 255

You must also know that when any substance is full of
electricity, if you bring your finger or a piece of metal near
to it, a spark will pass between the electrified substance and
your finger or the metal.

You will now, I think, be able to follow Franklin's
experiments. He put a person, whom we will call a, upon
a glass stool, and made him rub the metal cylinder of an
electrical machine with one hand and place his other hand
upon it to receive the electricity. Now, he said, if elec-
tricity is created by the rubbing, this person must be filled
with it, for he will be constantly taking it from the machine,
and it cannot pass away, because of the glass legs under the
stool. But he found that a had no more electricity in
him after rubbing the cylinder than he had before, neither
could any sparks be drawn out of him. He then took
two people, A and b, and placing each of them on a glass
stool, made a rub the cylinder, and b touch it, so as to receive
the electricity. Now notice carefully what happened, e was
soon so full of electricity that when Franklin touched him,
sparks came out at all points ; but what was still more curious,
when Franklin went to A and touched him, sparks came out
between them just as they had done between him and b.

This he explained as follows : ' a, b, and myself,' he said,
* have all our natural quantity of electricity. Now when a
rubbed the tube, he gave up some of his electricity to it, and
this B took, so that a had lost half his electricity and b had
more than his share. I then touched b, and his extra
charge of electricity passed into me and ran away into the
earth. I now went to a, and I had more electricity in me
than he had, because he had lost half his natural quantity,
and so part of my electricity passed into him, producinfr
the sparks as before.'

256 EIGHTEENTH CENTURY. pt. hi.

This Franklin believed to be the case with all electricity,
namely, that every body contains its own amount of it, but
that when for any reason it is distributed unequally, those
which have no more than they can well carry, give some up
to those which have less, till they have each their right
quantity. And this explained at once why a man cannot
electrify himself, for so long as he has no one else from whom
he can procure electricity, he is only taking back with one
hand what he gives out with the other. Those who had too
much electricity were called by Franklin positively electrified^
and those who had too little, negatively electrified, and from
this come the terms positive and negative electricity, which
are now used.

I should tell you here that it is now believed that
electricity is composed of two different kinds existing to-
gether in all substances. These two kinds are supposed to
remain at rest as long as they are equally balanced, but
when a body contains too much of one kind, it is always
trying either to give it up or to get some of the other kind
to balance it. This theory explains some facts which
Franklin's theory does not ; but it is not yet really known
what electricity is, only it is certain that Franklin was riglit
in saying that it is not created when we see its effects, but
only drawn out of bodies which contain it.

Franklin draws down Lightning from the Sky. — It
was in 1749, when he had already made most of his experi-
ments upon electricity, that Dr. Franklin began to consider
how many of the effects of thunder and lightning were the
same as those which he could produce with his electrical
machines. Lightning travels in a zigzag line, said he, and
so does an electric spark ; electricity sets things on fire, so
does lightning ; electricity melts metals, so does lightning.

CH. XXIX. FRANKLIN'S KITE. 257

Animals can be killed by both, and both cause blindness ;
electricity always finds its way along the best conductor, or
the substance which carries it most easily, so does lightning ;
pointed bodies attract the electric spark, and in the same
way lightning strikes spires, and trees, and mountain tops.
Is it not most likely that lightning is nothing more than
electricity passing from one cloud to another just as an
electric spark passes from one- substance to another ?

Franklin communicated these ideas to the Royal Society
in London, suggesting at the same time that, if he was right,
it would be possible to prevent a great deal of the harm
done by lightning by fixing upright rods of iron near high
buildings so that the electricity might run down from the
clouds into the earth without doing any harm. But this
notion seemed so absurd, even to clever men, that they
could not help laughing when his papers were read, and did
not even think them worth printing. You will easily un-
derstand that after this Franklin was ashamed to speak of
an experiment he meant to make by which he hoped to
bring down electricity from the sky. So we find that he
told no one but his son, whom he took with him upon this
strange expedition.

Franklin's idea was that if he could send an iron rod
up into the clouds to meet the lightning, it would become
charged with the electricity, which he believed was there,
and would send it down a thread attached to it, so that he
might be able to feel it. He took, therefore, two light strips
of cedar fastened crossways, upon which he stretched a silk
handkerchief tied by the comers to the end of the cross, and
to the top of this kite he fixed a sharp-pointed iron wire
more than a foot long. He then put a tail and a string to
his kite, and at the end of the string near his hand he tied

258 EIGHTEENTH CENTURY. pt. hi.

some silk (which is a bad conductor), to prevent the elec-
tricity from escaping into his body. Between the string and
the silk he tied a key, in which the electricity might be
collected.

When his kite was ready he waited eagerly for a heavy
thunderstorm, and, as soon as it came, he went out with his
son to the commons near Philadelphia and let his kite
fly. It mounted up among the dark clouds, but at first no
electricity came down, for the string was too dry to conduct
it. But by-and-by the heavy rain fell, the kite and string
both became thoroughly wet, and the fibres of the string
stood out as threads do when electricity passes along them.
Directly Franklin saw this he knew that his experiment had
succeeded ; he put his finger to the key and drew out a
strong bright spark, and before long he had a rapid current
of electricity passing from the key to his finger. The wise
men of London might now laugh if they pleased, for the dis-
covery was made j he had drawn lightning from the sky, and
proved that it was electricity ! Soon after this he made an
apparatus in his own house for collecting electricity from the
clouds, which rang a peal of bells when it was sufficiently
charged for him to make experiments with it. He also
introduced iron rods as lightning conductors, which were
for the future placed near all high buildings to attract the
lightning and carry it away into the ground.

Franklin had now earned a great name ; he was made a
Fellow of the Royal Society, and many honours were paid to
him by all the countries of Europe. He made many other
very valuable experiments, and was besides an active citizen
and politician. He died in 1790, in his eighty-fifth year,
after a life of hard labour and toil, for which, however, he
v/as well repaid by success.

CH. XXIX. ANIMAL ELECTRICITY. 259

Discovery of Animal Electricity by Galvani, and of
Chemical or Voltaic Electricity by Volta, 1789-1800.—-

Only a few months before Franklin died a new fact had
been discovered about electricity, which would have given
the old man great delight if he could have lived to see the
results. This discovery was made by Galvani, Professor
of Anatomy at Bologna, or perhaps we ought to say by
Madame Galvani, for it was her observation which first . led
her husband to study the subject.

Aloysius Galvani was born at Bologna in 1737, and we
know little of his early life except that, instead of becoming
a monk as he first intended, he married a professor's
daughter, and became the Lecturer on Anatomy in the
University of Bologna. He had in his house an electrical
machine which he used for experiments, and one day in
1789, as Madame Galvani was skinning frogs for a soup, one
of Galvani's assistants was working the machine near her.
Just as the flow of electricity was going on rapidly, this
. young man happened to touch a nerve of the leg of a dead
frog with a dissecting knife, and to his great surprise the leg
began to move and struggle as if it were alive. Madame
Galvani was so much struck by this that she told her hus-
band of it directly he returned, and he repeated the experi-
ment many times, and found that whenever the flow of
electricity from the machine was brought near the nerve of
the frog's leg it produced convulsions. He next tried
whether lightning brought down upon the nerves of the leg
would have the same effect, and the experiment succeeded
perfectly.

Meanwhile another accident showed him that the con-
vulsions could be produced without either lightning or an
electrical machine. He had prepared the hind legs of

26o EIGHTEENTH CENTURY. it. hi.

several frogs and hung them by copper hooks upon an iron
balcony outside his house. As they hung there the wind
swayed them to and fro, so that the ends of the legs touched
the iron of the balcony; and every time they did so
he noticed that the legs were convulsed just as they had
been by the electrical machine and the lightning. But this
time he could not see that any electricity had come near
them from outside, so he supposed that there must be an
electric fluid in the leg itself, which passed round every time
the two ends of the leg were joined by the metal. These
discoveries of Galvani soon became spoken of far and wide
under the name of galvanism, and the supposed fluid was
called the galvanic fluid.

Among the celebrated men who were attracted by this
new discovery was Alessandro Volta, Professor of Natural
Philosophy at the University of Pavia, who was bom at
Como in 1745, and was at this time a well-known naturalist.
Not satisfied with merely reading about Galvani's experi-
ments, Volta tried them himself, and he began to suspect
that the electricity was not, as Galvani imagined, in the frog's
leg, but was produced by the two metals, copper and iron,
upon which the legs had been hung, and which were acted
upon by the moisture in the flesh.

Then began a very famous controversy. Volta insisted
that the electricity came from the metals^ Galvani that it
came from the animal. In each new experiment which
Galvani brought forward to prove his point, Volta still
showed that the electricity could be produced without the
animal, until at last Galvani succeeded in finding a test
which he thought must silence Volta for ever. He found
that by laying bare a "nerve of the leg of a frog, called the
* crural nerve,' and bringing the end of it to the outside of
the muscles of the leg, he could produce the convulsions

CH. XXIX. GALVANI AND VOLT A. ' 261

without any metal at all. But Volta was not so easily con-
vinced ; he still insisted that it was the different fluids and
tissues being brought together which caused the electricity,
and that there was not a current running through the
animal. At this point, just when the truth would probably
have been worked out, Galvani died (in 1798), leaving
Volta in possession of the field ; and for twenty-eight years
no more was heard of animal electricity. We know now
that both the professors were right. Volta was right in
saying that the convulsion of the frog's legs on the balcony
was produced by the contact of the two metals in con-
nection with a fluid ; while Galvani was right in saying that
there is an electricity in animals which acts without any
other help. In 1826 an Italian named Nobili repeated
Galvani's experiment, and having then an instrument called
a galvanometer (see p. 351), by which the passage of the
faintest electric current can be detected, he proved that
such a current does exist in the frog, and it has since been
found to be common to all animals.

Meanwhile, however, Volta had also made a very re-
markable discovery, namely, that two different metals when
joined together in contact with moisture, and separated from
other substances, produce a current of electricity. This
may easily be tried in its very simplest form. If you take
a piece of copper and a piece of zinc and put one above
your tongue and one below it, you will feel nothing remark-
able so long as the two metals are kept separate, but directly
you let them touch each other at the ends, a tingling sensa-
tion will pass through your tongue, proving to you that an
electrical current is passing between the metals. If you put
the zinc under your upper lip, so that the copper may re-
main outside, you may, perhaps, even see a slight flash
when the two metals meet.

262

EIGHTEENTH CENTURY,

PT. III.

Volta found not only that it was necessary to have
moisture between the two metals, but that some acid put in
the water greatly increased the strength of the electricity.
Fig. 44 shows the first electric battery which he made, and
which is the one now commonly used for simple experi--
ments. In this battery each piece of zinc is joined to one
of copper, and where the two are not united they are in the
same cup, so that the liquid acts as a link to them. We
know now what Volta did not know, that a chemical change
is going on between the zinc and the acid water, which sets
the action going, but we do not yet know exactly what the
electricity itself is. The movement in Fig. 44 begins on the

Fig. 44.

Volta's Crown of Cups (Fownes).

z, Zinc, c. Copper, a a, h. Connecting wires. The arrows show the course of
the positive currents.

left-hand side at z. Here the current^ is set up by the
action of the acid and water upon the zinc, and is passed on
to the copper, c j then along the wire a, to the next z, and so
on till it reaches the last cup, when it is carried by the wire
b back to the first piece of zinc, and so the round is com-
pleted.

> There are always two currents passing along the wire — the positive
current, starting from the copper to the zinc, and the negative current,
going the opposite way from the zinc to the copper ; but to avoid con-
fusion, the positive current is always called the current^ and no notice
is taken of the other.

CH. XXIX.

THE VOLTAIC PILE.

263

This battery is called the ' Crown of Cups,' but though
it is so simple, it has not become as famous as the second
battery made by Volta, which is still called the ' Voltaic
Pile '"(see Fig. 45). In this battery the metals are laid one
above the other, and have small pieces of card or flannel
between them which are wetted with salt and water. The
battery ends with a plate of zinc at the bottom, and of
copper at the top, and these are connected by the wire, a a.
The action passes round this battery just as it did through
the cups, and if the wire, a a, is P^^

cut in the centre and tipped
with charcoal (which, being a
had conductor, causes the elec-
tricity to pass with difficulty),
a bright stream of fire will be
kept up between the points as
long as the battery is at work.
Such was Volta's discovery,
and we owe to it all the power-
ful galvanic batteries with
which our most valuable ex-
periments are now made. He
completed his Voltaic pile in
1800, just at the close of the
century, and even from this slight sketch you may see what
grand strides had been made in electricity during the past
fifty years.

Franklin had proved the real action of electricity, had
shown it to be the same as lightning, and had brought it
down from the sky. Galvani had proved its existence in
animals, and led the way to Volta's discoveries ; and Volta
had produced it in enormous quantities by two metals and

The Voltaic Pile (Fownes).

z, Zinc, c, Copper, a, a. Rod con-
necting the top layer of copper with
the bottom layer of zinc.

264 EIGHTEENTH CENTURY, pt. hi.

acidulated water, so as to keep up a constant flow, which
would travel any distance so long as the circuit was not
broken. Here, you will see, was the first step towards the
electric telegraph. It was but a commencement, anH for
nearly forty years no further advance was made ; but the
seed was sown, and when we reap the benefits we must
always remember the names of Franklin, Galvani, and
Volta, as the great pioneers in the science of electricity.

Chief Works consulted. — Lardner's Cyclopedia, ' Electricity,
Magnetism, and Meteorology ; ' * Encyclopsedias Britannica,* and
' Metropolitana,' art. 'Electricity;' Franklin's * Experiments and Ob-
servations on Electricity/ 1749; Priestley, 'On Electricity,' 1785;
Thomson's * Hist, of Royal Society,' 181 2; 'Life of Franklin,' by
himself, 1833; Bennett's 'Text-Book of Physiology;* Fownes's
• Chemistry ; ' Wilkinson's * Galvanism. '

ciL XXX. BRADLEY AND DELISLE, 265

CHAPTER XXX.

SCIENCE OF THE EIGHTEENTH CENTURY (CONTINUED).

Bradley and Delisls, Astronomers — Aberration of the Fixed Stars —
Nutation of the Axis of the Earth — Delisle's Method of Measuring
the Transit of Venus — Lagrange and Laplace — Libration of the
Moon accounted for by Lagrange — Laplace works out the Long
Inequality of Jupiter and Saturn — Lagrange proves the Stability
of the Orbits of the Planets — Sir William Herschel constructs his
own Telescopes — Discoveiy of a New Planet — Discoveiy of Binary
Stars — Herschel studies Star-clusters and Nebulae — Theory of
Nebulas being matter out of which Stars are made — The Motion of
our Solar System through Space — Weight of the Earth determined
by the Schehallien Experiment — Summary of the Science of the
Eighteenth Century.

Astronomical Labours of Bradley and Delisle. — And
now, as we approach the end of the eighteenth century, w^e
must take up once more the history of Astronomy, which we
have neglected since Newton died in 1727. Since that
• time many good astronomers had been occupied in making
different observations, but the only two who need be men-
tioned were Bradley, the Astronomer- Royal (bom 1692, died
1762), and Delisle (born 1688, died 1768).

Bradley explained two difficult astronomical problems ;
the first of these is called the * aberration of the fixed stars,'
which is an apparent movement of each fixed star in a small
circle in the heavens, but which is really the combined
effect of the yearly motion of our own earth, and of the time
which light occupies in coming down from the stars to us.
13

266 EIGHTEENTH CENTURY. pt. hi.

This question is very difficult, as is also his second discovery
of the nutation^ or slight oscillation, of the earth's axis j but
it is necessary to bear in mind that he made these obser-
vations, for they are very important in astronomy.

Delisle will interest you because he proposed a second
method of measuring the transit of Venus, which is now
used at stations where Halley's rule (see p. i6o) cannot be
applied. Delisle's method consists in marking the time at
which the transit is seen to begin in one part of the world,
and to end in another ; instead of measuring, as Halley did,
the duration or length of time occupied by the whole tran-
sit as seen at each place. It requires that the clocks of all
the different stations from which the transit is observed
should be set exactly to the same time, and then it answers
as well as Halley's.

These discoveries are all that need be mentioned during
the first half of the eighteenth century, but during that time
there had been bom within a few years of each other three
men, Lagrange, Laplace, and Herschel, who were to light up
the close of the century with the most brilliant discoveries.
The two first of these were Frenchmen, the last we may fairly
claim as an Englishman j for though he was born at Hanover
in 1738, of German parents, still Sir William Herschel came
over to England at the age of twenty-one, and all his dis-
coveries were made here. It was our King George III. who
gave him the pension which enabled him to devote himself
to science; and his son Sir John Herschel was, like his
father, one of our greatest astronomers, and made England
his home and country.

Lagrange and Laplace. — Louis de Lagrange was born
at Turin in 1736. His father, who had been Treasurer of
War, lost all his fortune when his son was quite a child, and

CH. XXX. LAGRANGE AND LAPLACE. 267

Lagrange often said that it was partly owing to this mischance
that he became a mathematician. His talent showed itself
so early that before he was twenty he was appointed
Professor of Mathematics in the Military College of Turin,
where nearly all his pupils were older than himself From
there he went to the Academy of Sciences at Berlin, and
remained twenty years, during which time he worked out
most of his celebrated problems. In 1787 he settled in
Paris, where he died in 18 13, at the age of seventy- seven.

Pierre Simon Laplace was the son of a farmer, and was
born at Beaumont-en- Auge, near Honfleur, in 1749. He,
too, began work very early in life, foi: in 1769 the famous
geometer D'Alembert was so struck with his talents that he
procured for him the chair of Mathematics in the Military
School of Paris, and from that time for more than fifty years
Laplace devoted himself to the pursuit of science, never
letting his active life as a politician interfere mth his
scientific studies. He died in 1827.

The work which was done both by Lagrange and Laplace
in astronomy was purely mathematical, and dealing as it did
with some of the most complicated movements of the
heavenly bodies, it cannot be rightly understood by any but
mathematicians. But some general idea may be formed of
the problems they solved, and we will take these in the
order of time, for they treated so much of the same questions,
one taking up the subject where the other left it, that it is
difficult to separate their work.

Libration of the Moon accounted for by Lagrange,
1764r-1780. — Long before the time of Lagrange it had been
known from observation that the moon always turns the
same side of her globe towards our earth as she goes round
it, so that we never see, and never can see, more than one

268 EIGHTEENTH CENTURY. pt. hi.

side of her surface, so long as she has the same movement
as at present.

In 1764 the Acaddmie des Sciences offered a prize for a
complete explanation of this curious fact, and Lagrange was
thus led to study the question, which he solved quite satis-
factorily in 1780.

Many people find it very difficult to understand how the
moon can be always turning round upon her own axis, as a
top spins, and yet always keep the same side towards us ;
therefore, it will be as well to make a simple experiment
which explains it quite clearly. Take a round ball and stick
a pin in one side of it, then turn the ball slowly round like a
teetotum, and notice as it goes round that the pin points
successively to each of the sides of the room one after the
Pj^ g other; then sew a piece oi

cotton to the side of the ball
opposite the pin, and fasten
the other end down to the

Diagram showing why one side of the table (aS at E, Fig. 46). If yOU
Moon is always turned towards the

Earth. now Toll the ball round the

'''' ?epJi?ndX"the^centS^^^ table, you wiU obscrvc that

i>, Pin to mark the side of the moon . , • • , , i • j r

which is never turned towards the the pm pomtS tO Cacll Side 01
earth. .-, . ...

the room m succession, as it
did before, showing that it has been turning slowly once
upon its own axis while going once round the point e, and
that, for this reason, the same side has been facing e all the
time.

This is the case with the moon as she travels round our
earth, and Lagrange proved mathematically that it must be
so, as Newton had already suggested, on account of the at-
traction of the earth upon the bulge at the moon's equator.
But Lagrange also showed that as the moon moves in an

CH. XXX. ORBITS OF JUPITER AND SATURN. 269

ellipse round the earth, and therefore goes at one time a
little faster, and at another a little slower, while her rotation
on her own axis does not vary, she doss not keep always
exactly the same face towards us, but we catch little glimpses
farther round her globe, sometimes on one side and some-
times on the other. This balancing movement is called the
llbration of the moon.

Laplace works out the Long Inequality of Jupiter and
Saturn, 1774-1783. — The next calculation about the planets
was made by Laplace, and is more difficult to understand.
You will remember that Newton showed that every planet^
attracts every other planet, and has some effect upon its path
round the sun. Now it had been found by comparing old
astronomical tables with later ones that these different
attractions had altered some of the ellipses in which the
planets move ; and both Lagrange and a celebrated mathe-
matician named Euler had tried to calculate these changes
and find out whether the planets would ever come back into
their old places. Laplace, however, carried the calculation
farther than either Lagrange or Euler had done, and he
showed that the whole machinery does work round in the
course of a long period. Only two planets, Jupiter and
Saturn, did not seem to follow this general law, but behaved
in a very eccentric manner; for it appeared that during
the seventeenth century Jupiter had been moving more
quickly every year and Saturn more slowly. If this went on
it was clear that Jupiter would draw nearer to the sun, and
at last fall into it, while Saturn would go farther off, and dis-
appear entirely from our system, and this would upset the
balance of our planets, and might lead eventually to our
being all drawn into the sun.

This v/as a very serious question, and it was a grand step

270 EIGHTEENTH CENTURY. pt. hi.

when Laplace answered it, and showed that there was no-
thing to fear, for that, odd as their movements appeared,
these two planets really obeyed the law of gravitation, and
would return to their old places like the other planets after an
immensely long period. He showed that their irregularity
arises from the fact that Jupiter travels two-and-a-half times
round the sun while Saturn travels once, and on this account
Jupiter is always catching Saturn up, so that the two planets
are often near together, or in conjunction^ as it is called.
When this happens, they pull each other so strongly that
they are drawn each out of its proper path. If they always
met in the same places, and so were pulled in exactly the
same direction, they would never right themselves again ;
but as Jupiter does not quite make three rounds while Saturn
makes one, their points of meeting vary a little each time,
and this brings them round at last to their old positions.
Laplace's calculation of this movement is called the long
inequality of Jupiter and Saturn.

Laplace also discovered the reason why the moon goes on
for a long time moving more and more quickly round our
earth, and then gradually more and more slowly. This pro-
blem, which is too long to examine here, was the last which
remained to complete the proof that Newton's theory of
gravitation would account for all the movements of the
heavenly bodies.

Xagrange proves the Stability of the Orbits of the
Planets, 1776. — And now, in the year 1776, came Lagrange's
great conclusion. He and Laplace had worked hand in hand,
proving more and more at every step how beautifully all the
heavenly bodies move in order, so that an equal balance is
preserved between them all. At last Lagrange, taking up
all the known facts and uniting them in one grand mathe-

CH. XXX. SIJ? WILLIAM HERSCHEL. 271

matical problem, proved that whatever might be the changes,
and they are almost infinite, caused by all the attractions of
the different planets on each other, yet in the course of long
ages every part of the solar system remains stable. Each
planet has its appointed road, along which it travels, through
many twists and turnings, but from which it cannot escape,
for the grand force of gravitation holds them all in one
eternal round about their sun.

These are some of the problems solved by Lagrange and
Laplace. You cannot expect to understand their full signi-
ficance, nor must you imagine that these few pages contain
more than a very small fraction of the work which these two
mathematicians accomplished. Laplace made some beau-
tiful calculations explaining the theory of the tides, and you
will also often hear him mentioned as the author of the
* Nebular Hypothesis,' by which he taught that our earth
and all the planets were in the beginning formed by the
condensation of gases and fluid matter. All this, which is
too difficult to enter upon here, is discussed in his famous
work, the 'Mecanique Celeste,' published in 1799. But
the main points to be remembered are that Lagrange
and Laplace proved the regular order of the movements of
the planets, and explained all those anomalies which had
seemed to be out of harmony with Newton's theory of gra-
vitation.

Sir William Herschel constructs Ms own Telescopes,
and discovers XJranus, 1781. — ^A\''illiam Herschel, who was
born in 1738, was one often children. His father, who was
an eminent musician, brought him up to follow his own
profession, and when William came over to England with
his regiment he started in life as a teacher of music. The
first three years in this country were years of hard struggle

272 EIGHTEENTH CENTURY. ft. ill.

and privation, but at last he was appointed organist at Hali-
fax in Yarkshirej and from there he went in 1766 to Bath,
where he soon became known as a talented musician, play-
ing in the Octagon Chapel and at concerts and parties with
immense success, and procuring a large number of private
pupils.

It was at this time, in the midst of active work which
kept him fully occupied all the day, that Herschel began
those nightly observations which have made his name famous.
His interest was at first excited by seeing the stars through
a small telescope only two feet in length j and his desire was
so great to be able to penetrate farther into the starry depths,
that he sent to London to order a large telescope. When
the answer came, however, he found that the price of the
instrument was quite beyond his means j and so determined
was he to carry out his project, that he set to work to con-
struct a telescope with his own hands. The first one an-
swered so well that he made several others, and at last
succeeded in completing one forty feet long.

From that time he spent the greater part of every night
in observing the stars, and on March 13, 1781, when he was
examining some near the constellation Gemini, or the
' Twins,' he caught sight of one star more conspicuous than
those around it. Struck by its size, he put a stronger mag-
nifying power on to his telescope, and found to his surprise
that this star became larger, while those round it remained
as small as before. The fixed stars, as you know, are so far
off that no magnifying power makes any difference in their
apparent size ; so Herschel began to suspect that this must
be a body very much nearer to our earth than the stars which
surrounded it. This led him to watch it, and he soon found
that instead of being fixed it moved onwards steadily. He

CH. XXX. THE PLANET URANUS. 273

thought at first that he had discovered a comet, but it was
not long before his wandering star was proved to be a new
planet, moving round the sun outside Saturn. This planet
is about half the size of Saturn, and takes more than eighty-
four years to go once round the sun. It was first called the
' Georgian star,' after George III. ; then it was called ' Her-
schel,' after its discoverer; and lastly it received the name
Uranus, which it still retains. It was through this discovery
that Herschel became known, and George III. gave him a
pension of 300 guineas a year, and a house near Windsor,
in order that he might devote himself entirely to astronomy.

Star-gauging and Discovery of Binary Stars, 1781-
1802. — One of the first tasks which Herschel undertook, was
to divide the stars into groups, according to their bright-
ness. Thus he classed the most brilliant as stars of the
first magnitude, those a Httle less briUiant as of the second
magnitude, and so on. While he was thus gauging^ or
measuring the distance of the stars by the intensity of their
light, his attention was arrested by some which appear
single when seen through a small telescope, but which prove
to be two stars when they are greatly magnified. A few of
these double stars were known already when Herschel began
to observe them, but he soon detected no less than 500
scattered about in different parts of the sky.

Now it had always been believed that these stars ap-
peared close together because one was almost directly behind
the other a long way off, just as two posts standing one at
some distance behind the other will appear to touch if they
are nearly on a line with your eye. But this explanation did
not satisfy Herschel, for he observed that many of these stars,
instead of merely passing to and fro in a straight line across
each other, as they would appear to do in consequence of

274 EIGHTEENTH CENTURY. pt. III.

the movement of our earth in its orbit, had another pecuHar
curved motion, as if they were both moving round some point
half-way between them. This movement was so slow that it
was twenty-five years before he could be sure about it ; but at
the end of this time he was able to tell the Royal Society
that these double or binary stars, as they are called, are not
one behind the other, but are actual pairs of stars moving
round and round each other, as if they were connected by a
rod suspended by its centre, and then set revolving !

To understand how great a discovery this was, it is neces-
sary to bear in mind that Newton had only been able to
prove that gravitation acts between the sun and the planets ;
but here was a reason for believing that even in the far-off stars,
miUions of miles away from our system, the same force is
holding distant suns together, and keeping them in their
orbits. This great discovery has been still more clearly
proved by later investigations, and groups of two, three, and
even more stars are now known, in which these bodies re-
volve round a common centre, held together by the force
of gravitation.

Herschel studies Star-clusters and Nebulae, 1786. — The
next discovery which Herschel made was quite as remark-
able as that of the binary stars. As long ago as the time of
Ptolemy (loo B.C.) five curious stars had been observed,
which he called * cloudy stars,' because they looked as if
they were covered by a mist ; and the number of these
cloudy masses had been increased by different astronomers
as time went on. When Herschel turned his attention to
them he discovered so many that, in 1786, he published a
catalogue of no less than a thousand, and added fifteen hun-
dred more a few years later ! Some of these bodies, such as
the bright spot called the 'beehive,' in the constellation

CH. XXX. STAR-CLUSTERS AND NEBULA. 275

Cancer, were simply clusters of stars which might be seen
distinctly through a telescope. In others the separate
stars couTd not be seen even with the strongest magnifying
power, but the group looked so much more distinct through
a powerful telescope than through a feeble one, that it seemed
most likely the stars were there, if only they could be dis-
tinguished. But a third set of cloudy bodies did not appear
in the least more separated, even with the largest telescopes,
and these Herschel called nebulcE, or clouds, because he
believed they were made up of mere masses of matter which
had not yet formed themselves into stars.

It was at this point that the grand thought forced itself
upon his mind that in these nebulae we might be looking
at the actual beginning of new worlds : and that the creation
of the different bodies of the universe was not begun and
finished long ages ago, but is even now going on under
our eyes. The nebulae he believed to be composed of star-
matter, out of which stars might be slowly forming, so as to
be first seen scattered like minute points in some of the more
hazy star-clusters, and then clearly visible, as in the ' bee-
hive ' in the constellation Cancer. In those days Herschel
could get very few astronomers to believe in this idea, but ^
you will see in the history of the nineteenth century how the
discoverers of the spectroscope (seep. 327) have proved that
some of the nebulae are made of gaseous matter ; so that it
becomes extremely probable that Herschel was right, and
that, in far distant space, star-mist is forming into stars, and
creating new suns to illuminate the universe.

The Motion of our Solar System through Space, 1783.
— The third and last theory which we can mention as coming
from Sir William Herschel is that of the motion of our sun
through space. In 1783 he showed from a study of the

276 EIGHTEENTH CENTCTRY, pt. in.

astronomical catalogues of past centuries that the stars do
not stand in exactly the same places with regard to us as
they did in ages gone by, and that, therefore, either we or
they must be moving through space. Now, when everything
around you appears to be moving backwards, it is most
likely, to say the least, that it is you who are moving forw^ards,
and not that all other things are in motion ; therefore Her-
schel concluded that the reason of the apparent change in
the place of the stars was the real movement of our sun and
its planets among them.

But, if such were the case, then there ought to be
one point straight in front of our path which would not
appear to move ; for if you walk into a forest you will
observe that the trees on either side appear to spread farther
and farther apart as you approach, but that those exactly in
front of you will not seem to change their places. Now
Sir W. Herschel found one point in the sky, in the con-
stellation Hercules, where the greater number of the stars
do not appear to move, while those to the right and the
left seem to be gliding off each in their own direction. He
therefore concluded that our sun is carrying the earth and
the other planets straight towards this point in the con-
*stellation Hercules. The rate at which this movement
goes on is not accurately known, but it must be very
great, probably at least as much as 150,000,000 miles every
year.

And here we must leave the discoveries of this great
astronomer, although we have only glanced at them very
superficially. The immense strides in astronomy made by
Laplace, Lagrange, and Herschel cannot be understood in a
moment ; and I wish you always to remember that you can
only gather crumbs of knowledge from this book, which

CH. XXX. THE DENSITY OF THE EARTH. 277

may, I hope, lead you to long and seek for more solid
food. Before, however, we take leave of Sir W. Herschel,
we must not forget to mention the faithful assistant who
was so great a help to him in his labours.

Wlien George III. gave Herschel his home and pension,
the astronomer sent to Hanover for his sister Caroline, and
she lived with him and received a small salary as his assist-
ant. She shared his night-watches and mapped down the
stars, star-clusters, and nebulae, as he came across them with
his slowly-moving telescope ; she helped to draw up his
catalogues, to write his papers, and to make his calculations.
In a word, she fulfilled one of the highest duties of a woman,
in becoming the patient helpmate of a great and noble mind ;
and for this reason although she never sought fame for her-
self, the name of Caroline Herschel will always be associated
with the labours of our great astronomer. Sir William died
in 1822, in his eighty-fourth year, leaving behind him a son,
the late Sir John Herschel, who will be mentioned in the
next chapter.

Determination of the Density of the Earth by the Sche-
hallien Experiment, 1774. — ^After speaking of the wonders
of the vast universe, and of suns so distant that we cannot
even guess at the space which lies between them and us, we
must now come back to our little planet and mention a re-
markable experiment which was made in 1774 by Maskelyne,
who was then Astronomer- Royal of England. This was the
finding out of the weight of the earth compared to its size,
or in other words, the density of the earth.

If our globe were made of one material, it would be easy
to weigh a small piece and multiply that by the size, which
we know pretty accurately, and so to get at the weight of the
whole. But as the rocks of the earth's crust differ very much

278 EIGHTEENTH CENTURY^ PT. in.

in weight, and we do not know what the middle of the globe
is made of, this plan is not possible. We know, however,
that every atom of matter has the power of attraction, so
that if we could find out how much attraction our earth pos-
sesses, by comparing it with the attraction of some other
body which we can weigh, then we could arrive at the weight
of the earth.

Now Newton, in his * Principia,' had pointed out that a
plumb-line, that is, a piece of string with a weight of lead at
the end of it, will not point straight to the centre of the
earth when it is held near a mountain, because the mountain
attracts the lead and draws it slightly towards itself. There-
fore, if the size and weight of the mountain were known, and
it were also known how great its pull is compared to the
pull of the whole earth, this would enable a mathematician
to calculate the weight of our entire globe.

A man named Bougler was the first to make this experi-
ment near a high mountain in Peru in 1738, but he suc-
ceeded very imperfectly, and in 1772 Maskelyne proposed
to the Royal Society to repeat the observation. Accord-
ingly, he went in 1774 to a very high mountain called Sche-
hallien, near Loch Tay, in Perthshire, and there he measured
the inclination or slope of the plumb-line on each side of
the mountain. You will remember that, according to the
theory of gravitation, the lead at the end of the line would
point straight to the centre of the earth c if the mountain
did not disturb it \ ^ and if the plumb-line is taken to two
places a certain distance apart and its inclination measured
by means of one of the stars overhead, it is easy to find out

• This is not strictly true, on account of bulge at the equator and
flattening of the poles ; but the discrepancy is of no importance to the

argument.

CH. XXX. THE SCHEHALLIEN EXPERIMENT.

279

Fig. 47.

exactly how much the lines d f will slope towards each
other when no mountain is between them. This measure-
ment being known, Maskelyne then made two observations,
one on each side of Schehallien, and found that in this case
the inclination, instead of being from d to f on each side,
was from e to f, because the mountain drew the lead towards
itself on either side. So the deflection e f d through which
the plumb-line was drawn
from the perpendicular showed
the difference between the pull
of the whole earth and the pull
of the mountain.

Then Dr. Hutton, the cele-
brated geologist, set to work
to find out the size and weight
of Schehallien. This he did
by surveying it and measuring
it in every direction, and then
taking pieces of the different
rocks it contained and weigh-
ing them carefully. When
this was done it was found
that the mountain pulled half
as strongly in comparison to
its size as the earth did for its
size. This showed that the materials in the mountain were
half as heavy as the average of those in the earth generally,
and as they were also about 2 J times as heavy bulk for bulk
as water it was proved that the whole globe is about five
times heavier than it would be if it was made entirely of that
fluid.

Schehallien Experiment for estimating
the Density of the Earth (Herschel).

A B, Surface of the earth, d, c, d, Angle
formed by the two plumb-lines point-
ing to the centre of the earth.
E, G, E , Angle formed by the two
plumb-lines when drawn aside by the
mountain M.

This calculation must be very near the truth, for the

28o EIGHTEENTH CENTURY. pt. hi.

chemist Cavendish obtained nearly the same result from
quite a different experiment made with a pendulum. This,
which is called the ' Cavendish experiment,' is too difficult to
explain here. In our own times. Sir Henry James, Sir
Edward Sabine, and others, have repeated these observations
and found them to be correct.

Summary of tlie Science of the Eighteenth Century. —

This sketch of the advance of astronomy brings us to the
end of the science of the eighteenth century ; for although
the greater number of the eminent scientific men of our day
were bom before the year 1800, yet their works belong
chiefly to the nineteenth century. Before going farther
therefore we must now look back and see how far science
has travelled since our summary of the seventeenth century.
Biology, or the science of life, had made great progress.
It had been enriched by the study of organic chemistry.,
founded by Boerhaave, by which we learn the elements of
which living bodies are composed ; by a more complete
knowledge of anatomy, or the structure of the body in all
its most minute parts, as Haller studied and represented
them in his anatomical works j and by a knowledge of
comparative anatomy, as taught by John Hunter ; or the Com-
parison of each organ as it appears in different beings, from
the lowest animal up to man. But even now the chief point
remains to be mentioned, for all these are of little use with-
out the study of physiology, or the science of living beings,
in which we must not only learn the great facts of the work-
ing of our own bodies and those of animals, but must take
into account the strange freaks of nature taught us by the
experiments of Bonnet and Spallanzani. In the history of
the nineteenth century we shall have to consider some of

CH. XXX.

SUMMARY. 281

these facts, and see how Cuvier, Lamarck, and Darwin have
carried out the study of physiology to great results in our
own day. But we have still more to include under Biology.
After learning the nature of living beings, we must have some
order of arrangement by which we can distinguish them.
Here we come to the work of Linn^us, one of the grandest
men of the eighteenth century. While Buffon was popular-
izing natural history, we find the great Swede patiently
working out all the minute characters and general features
of animals and plants, and reducing the whole kingdom of
life into such beautiful order, that after his time it could be
studied accurately and usefully by all who cared to take time
and trouble.

Thus, even without mentioning the science of medicine,
which has grown far beyond our power of following it up, or
the wonderful work with the microscope, which had increased
rapidly since the days of Grew and Malpighi, biology grew
during the eighteenth century into a group of sciences,
the works upon which would fill a library, and each branch
of which requires the study of a lifetime to master it.

Greology.— Side by side with biology arose about this
time the modest and almost unnoticed science of the earthy
then generally called physical geography, but now known as
Geology. This was a small seed sown in the eighteenth
century, to grow into a large tree only in our time ; yet it
was a great step when Scilla insisted that fossils were the
remains of living beings, and that the rocks containing them
were formed gradually under lakes or seas. And when
Werner taught men to study the earth's crust, and Hutton
forced them to see that Nature is, and has always been,
building up our present world out of the ruins of the past,
the foundations were laid for the real study of the earth and

282 EIGHTEENTH CENTURY. pt. hi.

its formation. Meanwhile William Smith toiled over Eng-
land, mapping out the position of each rock as he saw it, and
thus he led the way to a long series of careful observations,
by which the whole geology of England has been worked
out.

Chemistry. — But the science which before all stands
forth in the eighteenth century is cheinisUj) for here the
discovery of the different gases led to certainty where all had
been guess-work before, showing the actual chemical changes
which are taking place on all sides in the world around us,
and teaching men to weigh and test invisible substances, and
not to rest satisfied with their knowledge of any substance till
they had traced it home to its first and simplest elements. We
need not recapitulate here the different discoveries of Scheele,
Bergmann, Black, Cavendish, Priestley, and Lavoisier. You
will remember how they all helped to overthrow the
imaginary theory of Phlogiston, and to prove that combus-
tion and respiration are merely chemical changes taking
place between different substances and the oxygen of our
atmosphere ; and this truth is the starting-point of modern
chemistry.

Physics. — Of Physics I have told you but little in this
century, but the two points we have considered have caused
greater changes throughout the world than any previous dis-
coveries. When Black proved the amount of heat which is
lying hid in water and in steam, and when Watt applied
it to the steam-engine, a giant power was bom into the
world which has worked marvels. Visit any of the little
towns all over England and see the machines of all kinds
moved by the simple power of steam ; then go to the
great manufacturing towns and see the huge engines doing
the work of thousands of horses, with no other help than

CH. XXX. SUMMARY. 283

that of a man feeding the furnace with coals. Look at any
one of your own clothes, at the ironwork in all parts of your
house, from the rough heavy iron of fireplaces and fenders
to the delicate steel spring which moves the hands of your
watch ; look at the planks on your floors, and the carpets
which cover them ! All these have been woven, and forged,
tempered, sawn, and worked by steam machinery. Then
think of the way in which people are carried from one place
to another of the world ; so that in one month a man may
be in India, and the next in London j while food, clothing,
and goods of all kinds are spread over different countries in
a few weeks whenever they are wanted. And then remem-
ber that all this has sprung out of the latent heat of steam,
and its application by Watt to the steam-engine.

The next discovery is perhaps even more wonderful.
Franklin tries experiments upon the peculiar power known
by the name of electricity, and he suspects that it is every-
where and in everything. He proves its passage from one
body to another, and finds out many of its properties. In
spite of the derision of his friends, he seeks to bring it
down from the sky, and succeeds in making a prisoner of the
lightning and working with it in his own laboratory. Galvani
next finds this wonderful power hidden in the nerves of a
frog ; while Volta crowns the whole by showing how power-
ful electricity can be produced by two metals placed in a
little acid and water, and how this can be carried along
a wire of any length which touches the battery at both its
ends. Here lies hid the germ of the electric telegraph \ but
the grand secret of carrying messages from one end of the
world to another in a few moments was not to come yet.
That remained for the nineteenth century to accomplish.

Astronomy — Lastly we come to astronomy, and to some

284 EIGHTEENTH CENTURY. pt. hi.

of the most tremendous problems in the working of our
universe. Here we find Lagrange proving that the system
of our sun and planets is self- regulating, so that in spite of
all its infinite changes, there is no real irregularity or change-
ableness in its machinery, but all moves in one perfect and
constant round. Laplace shows the reason of those irregu-
larities which seemed to contradict Newton's law of gravita-
tion, and proves that they are all explained by that law,
thus completing the work of the great astronomer. Then
Herschel takes up the story, and after discovering a new
planet, he studies the cloudy nebulae, and points out the
probable formations of new suns going on now in far-distant
regions; he pictures our own sun rushing through space at
the rate of 150,000,000 miles a year, carrying with it our
earth and all the other planets ; and above all he traces
the law of gravitation into the distant star- world, and shows
it there holding suns together and causing them to revolve
round each other. And so, out into space as far as the
mind can reach, we find everlasting order reigning through
out the visible universe.

List of Works consulted. — Herschel's 'Astronomy;' Arago, *Vie
et travaux de Herschel,' 1S43 ; Proctor's 'Essays on Astronomy,'
' The Universe, ' 'Other Worlds than Ours' j Grant's 'History of
Physical Astronomy ; ' Arago, ' Eloge of Laplace ; ' Airy's ' Astro-
nomy ; ' ' Encyclopsedia Britannica ' — ' Astronomy ; ' ' Orbs of
Heaven,' Mitchell.

SCIENCE OF THE
NINETEENTH CENTURY

Some of the Chief Men of Science of the i<^tk Century
who are mentioned in the following pages.

Piazzi

Olbers .

Encke

Gauss

Sir J. Herschel

Airy

Adams .

Leverrier

Galle .

Schwabe

Young .
Malus
Fresnel .
Arago
Seebeck .
Oersted .
Ampere .
Brewster
Sabine .
Fraunhofer
Wheatstone
Bunsen .
Kirchhoff

A.D.
I 746- 1 826

I 758-1 840

I79I-I865

I777-I855
I792-I87I

1 80 1, living
1818, living
181 T, living
18 12, living
1788-1875

1773-1829
1775-1812
I 788-1 82 7
1786-1853
1770-1831
1777-1851
1779-1864
I 784-1 868
1 788, living
I 787-1 826
1802-1875
181 1, living
1824, living

Huggins

A.D.

1824, living

Miller .

1817-1870

Wollaston

1766-1828

Biot

. I 774-1862

Berzelius

1779-1848

Dalton .

. 1767-1844

Davy .\

. 1778-1829

Faraday'.

1791-1867

Liebig .

. I 803- I 873

Humboldt

. 1767-1835

Buckland

. 1 784-1856

Lyell .

. 1797-1875

Agassiz .

. 1807^1873

Lamarck

. I 744-1829

Goethe .

I 749-1833

Cuvier .

I 769-1 832

G. St. Hilaire

1 772-1844

Von Baer

1792, living

Boucher de Perthes

I 788-1868

Wallace .

1822, living

Darwin .

1809, living

CH. XXXI. ASTRONOMY. 287

CHAPTER XXXI.

SCIENCE OF THE NINETEENTH CENTURY.

Difficulties of Contemporary History — Discovery of Asteroids or
Minor Planets between Mars and Jupiter — Dr. Olbers suggests they
may be fragments of a larger Planet — Encke's Comet, and the cor-
rection of the size of Jupiter and Mercury — Biela's Comet noticed
in 1826 — It divides into two Comets in 1845 — Irregular movements
of Uranus — Adams and Leverrier calculate the position of an un-
known Planet — Neptune found by these calculations in 1846 — A
Survey of the whole Heavens made by Sir John Herschel— His
work in Astronomy — Comets and Meteor- systems.

We have now arrived fairly at the beginning of our own
century, and shall have to speak of events which happened
as it were but yesterday, and of men whom our grandfathers,
or even perhaps our fathers, have seen and known. How
are we to find our way through the mass of discoveries
which have been made in every science during the last
seventy years, or to make our choice among the number of
famous men whose names we meet with every day ? We
must begin at once by recognising that it is impossible to
mention all, even of the leading points, of the science of our
time, and then we may try to learn a few of them, if we do
so with a clear understanding that we are leaving important
gaps unfilled.

There are two special difficulties which we must en-
counter in the history of this century; first, we cannot
avoid mentioning the work of some living men, while at the

288 NINETEENTH CENTURY. pt. in.

same time we omit others who are equally eminent ; and
secondly, we must speak of many subjects which are still, as
it were, on their trial, and which will not be finally settled
till they can be judged dispassionately by future generations.
I have tried, however, to follow as far as possible the plan I
adopted in the earlier centuries, of mentioning only a few
great men whose work you can understand and follow; and
stating on doubtful subjects what is the opinion of those who
are best able to judge from the evidence. Therefore you
must constantly bear in mind that this last portion of the
book cannot be said to contain a history of the science of
the nineteenth century, but only an account of a few of the
leading discoveries and theories of our times and of the men
who made them.

Advance in Astronomy. — The science of Astronomy, in
particular, has spread far beyond our power to follow it.
We have seen that astronomers up to the end of the
eighteenth century were always striving to work out the laws
which govern the movements of the heavenly bodies. The
key to this problem was found by Newton, and the work was
completed when Laplace and Lagrange showed that even
those planets which seem to have the most irregular orbits
are really governed by the force of gravitation. From that
time astronomy became really an exact science, and men had
only to make their calculations with perfect accuracy in
order to be able to foretell what was going to happen ; or if
they failed, then they knew there must be some other un-
known heavenly body (such as Neptune, p. 294) causing the
irregularity. Therefore, the science of astronomy in our
century has been chiefly occupied in discovering new planets,
stars, and star-clusters ; at every step giving us new proof
that gravitation rules throughout the visible universe. And

CH. XXXI. ASTEROIDS OR MINOR PLANETS. 289

side by side with this has grown up a new study, namely
that of the nature of the sun, planets, stars, comets, meteors,
&c., telling us what they are like in themselves, whether they
have an atmosphere like our own, and of what materials
they are made. This study has been carried on partly by
powerful telescopes, but chiefly by the wonderful method
called spectru77i analysis, of which we shall speak presently.
Meanwhile we must first begin by naming a few new bodies
lately observed in the heavens.

Discovery of the Asteroids and Minor Planets between
Mars and Jupiter, 1801-1807.— Not long after the dis-
covery of Uranus, a well-known astronomer named Bode
pointed out that the distances of the planets from the sun
seemed to follow a remarkable arithmetical law. The only
exception to this law was between Jupiter and Mars ; and
here the gap was t\vice as large as it ought to be according
to the calculation. Therefore astronomers suspected that
there must be a planet between these two which had not
yet been seen ; and in the year 1 800, at a meeting at Lilien-
thal, in Saxony, they agreed to search diligently for this sup-
posed missing body.

Signor Piazzi, the Astronomer of the Observatory at
Palermo, in Sicily, was one of these planet-searchers, and on
the first night of the year 1801 he caught sight of a small
star in the constellation Taurus, which had not yet been
noticed in any catalogue. The next night he looked for it
again, and found that it had moved its position. He did
this for twelve nights, and the movement seemed to show
that it was the planet he was seeking. Just at this point,
however, he was taken ill, and although he had told other
astronomers of what he had seen, no one could find the
planet again. Months passed, and people began to doubt
14

290 NINETEENTH CENTURY. pt. iii.

whether he had not made a mistake ; but at last a young
German astronomer named Gauss set to work to calculate,
from the facts which Piazzi had given, whereabouts in the
heavens the planet ought then to be, and turning his tele-
scope to the point, there he found it ! This planet was
called Ceres; it was very small compared to the other
planets, but the astronomers were satisfied at having filled
up the supposed gap.

Before two years had passed away, however, in the year
1802, another astronomer, Dr. Olbers, of Bremen, suddenly
announced that he had found another little planet near
Ceres, which he called Pallas, and in 1804 a third was found
by another astronomer named Harding, who called it Juno.
It seemed very strange that so many bodies should be
moving round the sun at nearly the same distance from
it, and Dr. Olbers suggested that they might perhaps be
parts of one large planet which had broken up into fragments.
If this was so he expected to find more, and truly enough in
1807 a fourth was discovered, which he called Vesta. In
1845 and 1847 two more were added to the number.
Since then some have been found every year, till now no
less than 153 of these small planets, or asteroids as they
are called, are known to be moving round the sun be-
tween Mars and Jupiter. Pallas, the largest of these, only
measures about 600 miles across, and when it comes nearest
to the earth does not look larger than a star of the eighth
magnitude. Whether they are really fragments of a planet is
not proved, and we have still a great deal to learn about them.

Encke's Comet, 1819. — The next bodies of interest which
were discovered were two returning comets, each of them
remarkable for different reasons. The first of these was
observed in 181 9, through the telescope at Marseilles, by a
Freiicliman named Pons. It was very small, and is mainly

CH. XXXI. RETURNING COMETS, 291

of importance because after Professor Encke, of Berlin, had
calculated that it returned regularly every three years and a
quarter, he found that it arrived two hours and a quarter
earlier each time. "Why it should come earlier is a question
which is still very perplexing to astronomers, though several
explanations have been suggested. In order to find out
how fast this comet moved, Encke was obliged to calculate
very accurately how much the different planets attract it ;
and this led him to discover that Jupiter is larger than the
earlier astronomers had supposed, while Mercury is much
smaller.

Biela's Comet, 1826. — In 1826 another remarkable
comet was observed by an Austrian officer named Biela,
and on that account called * Biela's comet' M. Clausen, a
German astronomer, computed that it revolved in an elliptic
orbit in a period of six years and eight months, and it was
then shown to be the same comet which had been observed
in 1772, 1805, and 1818. This comet has had a very curious
history. In the year 1832 great alarm was excited because
the astronomers calculated that it would cross the orbit of
our earth on October 29. People who did not understand
the question thought this meant that it would run into us
and perhaps destroy our earth ; and many even sold their
houses and land because they thought the end of the world
was at hand. The people in Paris especially were so
frightened about it that the Academy of Sciences were
obliged to ask Arago, the French astronomer, to quiet their
fears, and he wrote a popular essay showing that though the
comet crossed the path of our earth, yet on that day we
should be fifty-five millions of miles away from the spot.

But it was in 1845 ^^^ Biela's comet proved most
interesting. On November 26 in that year it came at the

292 NINETEENTH CENTURY. pt. hi.

time it was expected, and was seen each night afterwards as
usual till January 12. On that night, however, when
Lieutenant Maury looked at it from the observatory at
Washington, in the United States, he saw, not one comet, but
two distinct and separate comets moving along together. This
seemed so strange that it would scarcely have been believed
if several astronomers had not watched the comet for
more than a month, and satisfied themselves that it had
really split up into two parts, each part being a perfect
comet, with a bright head and a glowing tail ! These two
comets returned in 1852, still keeping each other company
at the same distance apart as in 1846, but since then they
have never been seen again. Many other comets have been
discovered besides these, and we know that many thousands
or even millions must be wandering through space, but of
these we cannot speak here.

Adams and Leverrier determine the Position of an
Unknown Planet by its Influence on the Orbit of Uranus,
1843-1848. — The next discovery which we must consider is
one of the most remarkable in the history of astronomy,
because it was not made with the telescope but was worked
out independently by two men entirely by means of Newton's
theory of gravitation. You will remember that in 1781 Sir
William Herschel discovered the planet Uranus moving out-
side all the other planets (see p. 272). Now many astrono-
mers had noticed this body in earlier ages, and supposing it
to be a star, had marked its position from time to time in the
heavens, and from these observations it was now possible
to calculate its path round the sun. When this was done
it was found, however, that the planet did not move as
it ought to do according to the theory of gravitation. The
pull of the sun and the known planets did not account for

CH. XXXI. DISCOVERY OF NEPTUNE. 293

its orbit, for it roamed farther out into space than it should
do if they were the only bodies which attracted it. Either,
therefore, the early astronomers had marked the position of
the planet wrongly, or some unknown and unseen body
m-ust be pulling it out of its course. This last seemed the
most likely explanation, but no such planet could be seen,
and the problem remained unsolved.

It was at this point that a young student of St. John's
College, Cambridge, named John Couch Adams, then only
twenty-three years of age, made a memorandum in his note-
book to work out the movements of Uranus, and see if by
this means he could discover whether there was another
planet farther away from the sun. As soon as he had taken
his degree as Senior Wrangler in 1843, ^^ set to work to
carry out his intention, and two years afterwards he sent a
paper to Mr. Airy, the Astronomer-Royal at Greenwich,
stating in what part of the heavens astronomers ought to
look for the unknown planet which would explain the
capricious movements of Uranus.

It is not easy for any but mathematicians to understand
what a wonderful thing it was to calculate accurately, in this
way, where a planet would be found which had never been
seen. When Pallas was discovered between Mars and Jupi-
ter, Piazzi saw it through the telescope for some days, and
it was only found again by following out the movement
which he had recorded. But in Adams's case nothing had
ever been seen, and the only reason for suspecting anything
to be there, was that astronomers could not make their very
difficult calculations of the attraction of the different planets
come out right. Adams, therefore, had first to calculate all
the attractions of the sun and the planets, in their different
positions, and then to find out how they would affect Uranus

294 NINETEENTH CENTURY. pt. in.

in his path ; and wherever the planet did not follow their
pulling he had to calculate where another body must be to
draw it away from them. This he accomplished, and it is
very remarkable that the great living French . astronomer
named Leverrier also worked out the same problem, without
having heard that Adams had done it

In the year 1839 Leverrier had begun a long series of
calculations (which were only completed last year, 1874), to
find out the varying attractions, and by that means the size
and weight, of the different planets, and while he was at
work at this he became convinced that there must be some
unseen body pulling at Uranus. Now it so happened that
just at the time when Adams and Leverrier began to feel
after this supposed planet, Uranus had lately been very much
disturbed, and so they knew that the disturbing cause must
have approached near to him, and this showed them in
which part of the heavens the attracting planet ought to be.

Leverrier published his calculations in the Journal of
the Academie des Sciences at Paris for June 1846, and when
the Astronomer- Royal read the paper he was astonished to
find that the French astronomer had fixed the place of the
unknown planet within one degree of the spot which Adams
had named. This led him to read Adams's paper again
more carefully, and to put the two astronomers into com-
munication with each other ; and the consequence was that
Leverrier wrote another paper in August 1846, stating still
more accurately where the planet ought to be found. This
paper he sent to his friend M. Galle, of the Berlin Obser-
vatory, on September 23, 1846, asking him to look for
the planet in that part of the sky which he pointed out. M.
Galle did so, and on that sa??ie night, by foUoming the instruc-
tions of the two astronomers^ he found the unknown planet.

CH. XXXI. SIR JOHN HERSCHEL. 295

So true is the law of gravitation that two men sitting at
home in their studies were enabled, from slight irregularities
in the motion of Uranus to predict the existence and place
of a disturbing body, rolling on through space ! This new
planet is called Neptune, and is a little larger than Uranus;
it has certainly one moon, discovered by M. Lassell, and
Herr Struve thinks he has seen a second.

Sir John Herschel's work in Astronomy. — While these
different discoveries were being made in the observatories of
Europe, Sir John Herschel was carrying on the work his
father had begun of gauging or measuring the brilliancy of
the stars. Born at Slough, close to his father's observatory^,
in 1792, the young John Herschel spent his early life with
his father and aunt, and saw them always busy night and
day studying the heavens. In 18 13 he was Senior Wrangler
at Cambridge, and after that he turned his attention to
double stars, and in 1828 completed a list of no less than
2,000 of these wonderful double and sometimes treble suns
which revolve round each other. When he had completed
the survey of the whole of our northern skies, he went in
1833 to the Cape of Good Hope, where an observatory
had been built in 1820, and there he spent four years
gauging the stars of the southern hemisphere and classing
them according to their brilliancy, as his father had classed
those of the northern hemisphere. He was thus the first
astronomer who swept his telescope over the whole of the
heavens which are visible from our planet, and who saw
with his own eyes every star, planet, and nebula then
visible in the sky. Among the remarkable appearances
which he examined were those cloudy masses of light called
the Magellanic Clouds^ which are the Milky Way of the
southern hemisphere, and he found them to be made up of

296 . NINETEENTH CENTURY. pt. hi.

Stars, star-clusters, and nebulas, mingled together in wonder-
ful complexity.

When he returned to England in 1838, you can imagine
what a wonderful picture he must have had in his mind of
the whole universe as far as we can see it. It was then that
he wrote his famous ' Outlines of Astronomy,' which was a
new edition of a little book he had written years before. In
this great work Sir John Herschel first taught ordinary
people what a grand science astronomy is. Before his time
the different discoveries and theories had been scattered
about in various scientific papers, too difficult and too
tedious for the public to read. But Sir John wrote simply
and plainly about the great truths which had been worked
out from the days when Aristarchus first asserted that the
earth moved round the sun to the time when Sir William
Herschel pictured our whole solar system travelling onwards
through endless space ; and through his book many who
would never otherwise have studied the science learnt to
know something of the wonders of the heavens and the
lessons they teach. Sir John was a true lover of the works
of nature, and he taught all his readers to love them too,
and to feel a true reverence for the Infinite Mind of the
Creator of them all. He died in 1871, and was buried in
Westminster Abbey, but never will those who knew him
forget the beautiful truth-loving spirit which breathed in
every word he wrote or spoke.

Sir John Herschel is the last of our great astronomers
who is no longer living, and here we should close the history
of physical astronomy, if it were not that a wonderful disco-
very has been made within the last ten years which must at
least be mentioned.
Discovery of the Paths along which Meteors travel,

CH. XXXI. METEORS. 297

and the Agreement of two of these with the Orbits of Re-
turning Comets, 1862. — Everyone has heard of falling or
shooting-stars, and most people have probably seen one or
more of these bright meteors rush across the sky on a calm
summer evening, and then vanish as suddenly as it appeared.
The rude Lithuanian peasants have a touching legend about
these falling stars. 'To every new-born child,' they say,
* there is attached an invisible thread, and this thread ends
in a star ; when that child dies the thread breaks, and
the light of the star is quenched as it falls to the earth.'
Science has taught us a different, but a not less wonderful
history. It is now known that these meteors are solid
stones, 'pocket planets' as Humboldt called them, which
travel round the sun in the opposite direction to that in
which we are going, "WTien we meet them they rush through
our atmosphere so fast that they become heated, and give out
light for a short time till they are burst into fine dust and
vanish. When they are too large to be consumed before
they reach the earth, they fall, often with great violence, and
are split into countless fragments. A large collection of
these meteoric stones is to be seen in the British Museum,
some weighing hundreds of pounds, others only a few grains.
They have been analysed, and are found to be composed
chiefly of iron, tin, sulphur, olivine, and oxygen.

Before the present century all that was known about these
bodies was very vague and unsatisfactory. From time to time
accounts of stone-falls came from different parts of the world,
but they were not much attended to, and people found it
difficult to believe that stones and mineral masses actually
fell from the sky on to the earth. But in 1803 a fiery globe
was seen to rush over the town of Aigle, in Normandy, and a
stony mass was dashed to the ground and shattered into

298 NINETEENTH CENTURY. pt. hi.

thousands of fragments, some of which weighed as much as
1 7 J lbs. This created so much astonishment that the French
Government sent M. Biot, a celebrated French chemist, to ex-
amine into the matter, and he reported that there could be no
doubt that a shower of hot stones had fallen upon the earth.

From this time more interest was taken in meteors and
meteoric stones. People had remarked for a long time that
shooting-stars were more abundant from the 9th to the nth
of August than at other times, and more lately it was also
noticed that a shower of the same kind happens about the
T3th of November. Astronomers began, therefore, to think
that these meteors must move in regular orbits, crossing
the orbit of our earth in certain places, so that we pass
through them. There were also reasons for thinking that
the November meteors travelled in an enormous ellipse,
passing at one end even outside the planet Uranus.

It was not, however, till thirteen years ago that anything
was really known. In the year 1862 an Italian astronomer
named Schiaparelli made a very remarkable suggestion. He
noticed that a comet which was seen in that year crossed the
earth's path just at the point where we are always in the
middle of the meteor- shower on August 10, and it occurred
to him whether it might not be possible that the August
meteors were travelling in the same orbit as the comet. His
guess turned out perfectly right, and by a calculation which
we cannot follow here he proved that the comet and the August
meteors travel along ;precisely the same path in the shape of a
long ellipse passing at one end outside the planet Neptune,
the most distant of the known planets. This was the first
time that the orbit of any set of meteors had been traced
out.

The next was that of the November meteors, which was

CH. XXXI. METEOR-SHOWERS. 299

determined by Adams, and also independently by Leverrier.
It had been shown by searching out all the past accounts of
November showers that in times gone by, the earth passed
through these meteors a little earlier in the year than she
does now, and this could not be accounted for by any
irregularity in the movement of the earth. It looked there-
fore as if the orbit of the November meteors must be slowly
shifting, just as the orbits of the planets do, within certain
limits. It was upon this shifting that Adams founded his
calculations, and he worked out the meteor path with great
accuracy, showing that those astronomers had been right
who thought it extended beyond Uranus. This time the
problem was solved by pure astronomical reasoning and not
by a happy guess. But perhaps the most remarkable part
of the story is that in 1866, long after Adams had deter-
mined the orbit, a new comet was seen which was found to
move exactly along the path of the November meteors, in the
same way that the comet of 1 8 1 2 agrees with those which
fall in August.

Although these two meteor-showers are the most impor-
tant, they are by no means the only ones crossed by our earth.
Any clear night, if you watch carefully, you may see (according
to the astronomer Proctor) about six shooting- stars in one
hour; and Professor Newton, of America, has calculated that
7,500,000 meteors large enough to be seen without a telescope
pass through our atmosphere in one single day and night.
At least a hundred sets of meteors, or meteor-systems as they
are called, are known to astronomers, and each one of these
is composed of millions of bodies; and you must bear in
mind that these systems do not move round us, but round
the sun, so that it is only because we happen to cross their
path that we know anything of them. It would be idle to

300 NINETEENTH CENTURY. pt. hi.

suppose that these hundred meteor- systems which we come
across are the only ones existing. On the contrary, we
have every reason to think that they are only a few out of
thousands of meteor-systems which we never meet, and
which must grow more numerous the nearer they approach
the sun.

And so we arrive a,t the wonderful thought that the
whole of our solar system is swarming with meteors rushing
along with immense speed ! What their use is we do not
know. Some astronomers imagine that the heat of the sun is
kept up by these meteoric stones falling in countless myriads
on his face, but this is disputed by others ; and for the pre-
sent it is enough if we can picture to ourselves these rings
of meteors whirling round and round in space, and flash-
ing into light as they rush through our atmosphere whenever
we happen to cross their path.

I have chosen out these new facts about meteors be-
cause, of all modern discoveries, they give the best idea of
the wide fields of knowledge which are opening out before
us. Within the last fifty years a number of most interesting
observations have been made about the nature of the sun
itself; but they would require long explanations, and being
all the work of living men they scarcely belong to our
history.

In the chapter on Spectruni Analysis we shall learn some-
thing of the atmosphere of the sun and stars, and in the
chapter on Magnetism something of the spots on the sun
and their effects on our earth. But for the history of the
discovery of the photosphere, corona, red prominences, and
other wonderful appearances upon the face of the sun, you
must read special works on the subject.

CH. XXXI. ASl^RONOMICAL WORKS. 301

Chief Works consulted. — Airy's 'Report on Astronomy,' British
Association, 1833 ; J. D. Forbes's * Progress of Mathematical and
Physical Science ' — Sixth Dissertation ; ' Encyclopaedia Britannica,'
new edition ; Guillemin, * The Heavens ; ' Herschel's 'Astronomy ;'
Grant's ' Physical Astronomy;' 'Reports of the Astronomical So-
ciety;' ' The Orbs of Heaven,' Mitchell ; Proctor, ' On Shooting-
Stars and Meteors.'

302 NINETEENTH CENTURY. pt. hi.

CHAPTER XXXII.

SCIENCE OF THE NINETEENTH CENTURY (CONTINUED).

Discoveries concerning Light made in the Nineteenth Century — Birth
and History of Dr. Young — He explains the Interference of Light
— Cause of Prismatic Colours in a Shadow — And in a Soap-bubble
— Malus discovers the Polarization of Light caused by Reflection —
Birth and History of Fresnel — Polarization of Light explained by
Young and Fresnel — Complex Vibrations of a Ray of Light — How
these Waves are reduced to two separate Planes in passing through
Iceland Spar — Sir David Brewster and M. Biot explain the colours
produced by Polarization.

We must now go back to the history of Light, which we left, as
you will remember, at the end of the seventeenth century, at
the point which Newton and Huyghens had reached. During
the whole of the eighteenth century very little was learnt about
this science, and it remained for the men of our own time to
make the next step and to discover the grand laws of light
which we must now consider. It will be best to divide our
subject into two parts — ist. The discoveries which have led
to a true Theory of Light. These are very difficult to under-
stand, and you must not expect to gain more than a slight
notion of them ; 2nd. The new facts lately discovered about
the Chemistry of Lights and called Spectrum Analysis, and
of these I hope you may understand enough to fill you with
delight at the beautiful histories they reveal.

Discovery of the Interference of Light by Young, 1801. —
You will remember that Newton and Huyghens had proposed

CH. XXXII. DR. THOMAS YOUNG, 303

two different theories of light (see page 174). Newton's,
called the Corpuscular or Emission Theory, supposed light to
be made up of minute particles darting out from the sun and
every light-giving body. Huyghens, on the contrary, taught
that light is produced by the vibrations or waves of an in-
visible ether which is supposed to fill all space. This was
called the Undulatory or Wave Theory.

Newton's authority was so great, and the experiments he
made to prove his theory were so striking, that the * Corpus-
cular theory ' was generally received as the true one, espe-
cially as Huyghens had only made a few simple experiments
in support of his idea ; and it was more than a hundred
years after Huyghens first published his ' Treatise on Light '
before a man arose to defend the Undulatory theory and to
bring it again into notice. This man was Dr. Thomas Young,
the first Professor of Natural Philsophy at the Royal Insti-
tution of London.

Thomas Young, who was the son of a Quaker, was born
at Milverton, in Somersetshire, in 1773, ^"^^ died in 1829.
He was brought up at home, and seems to have been a very
clever lad, for he knew seven languages at the age of four-
teen, besides having studied Natural Science as an amuse-
ment. He then went to the Edinburgh University, where he
worked under dear old Dr. Black, whose enthusiasm, no
doubt, helped much to increase his love of science. When he
was only twenty he sent a paper on ' Vision ' to the Royal
Society, and was elected a member the following year. He
then went to Cambridge in order to be able to satisfy the
College of Physicians, and practised as a medical man in
London, where, in 1801, he was also made Professor of
Natural Philosophy at the Royal Institution, which had just
been founded, and Editor of the Nautical Almanack He is

304 NINETEENTH CENTURY, pt. iii.

very famous as one of the first men who deciphered the
Egyptian hieroglyphical writings, and yo.u will often hear
him mentioned as an Egyptian scholar \ but what we have
now to consider are his discoveries about Light.

Young tells us himself that it was in May 1801 that he
first made an experiment which seemed to him to prove
that light must be a succession of tiny waves moving across
space as Huyghens had supposed. His experiment was the
following. He made a hole in the window-shutter of a
dark room, and covered it with a piece of thick paper, in
which he had pricked a small hole with a needle. He then
put a small looking-glass outside the shutter, so as to throw
the sunlight very fully upon the hole and send a cone of
spreading light through it. In this cone of Hght he held a
very narrow strip of card and watched the shadow which it
threw on the wall, or on another piece of card behind it.
On each side of the shadow there were some faint fringes of
colour, but besides these he saw in the shadow //i"^^ dark and
light upright bands, which finished off in a faint white band
in the middle of the shadoAv. It was from these faint bands,
which many men would have thought not worth noticing,
that Young worked out the truth of the Wave Theoiy of
Light.

The first question he asked himself was — ' Why should
there be any light at all in the shadow ? ' This was not
difficult to answer, for as light travels in all directions, a part
of it, passing on each side of the strip of card, will spread
out behind it. But why should this light arrange itself in
stripes and not fall equally all over the shadow ? It seemed
at first impossible to explain this; but when Young placed
his hand so as to prevent the light passing along one of the
edges of the card he found that the fi'inges or bands dis-

CH. XXXII. INTERFERENCE OF LIGHT. 305

appeared enth'ely^ and when he took away his hand they
returned. It was clear, then, that so long as the Hght passed
in one direction only behind the card it spreads itself out
equally, but directly the two sets of rays from the two sides
met each other, dark and light bands appeared.

Now Newton's emission theory would give no explana-
tion of this curious fact, for if light were made of tiny par-
ticles there is no reason why these particles in crossing each
other should make dark bands. On the contrary, the more
of them there were the more light there ought to be. The
Undulatory or Wave Theory, however, explained the bands
perfectly, and this we must now try to understand.

You will remember that Huyghens supposed an ether
filling all space to be set in motion by the sun, or any other
luminous body, and to heave up and down in tiny waves just
as the sea heaves, or the water of a pond when you agitate it.

Suppose, therefore, that a number of waves of water, all
of the same size, are moving along one side of a lake as at a,
Fig. 48, p. 306, and flowing out through a narrow channel at
the end, and suppose another set of waves to be moving along
the other side, b, so that the two sets meet at the mouth of the
channel. Then, if the two waves c and d are both rising up
when they meet, they will join together into one large wave,
and will continue to flow in large waves down the channel.
But if they meet, as in Fig. 49, when c is falling and d is
rising, then c will flow into the hollow of d and fill it up,
and instead of a large wave being made, the surface of the
water will become smooth.

Now Young pointed out that this is exactly what happens
to the undulations of light. After passing through the hole
in the shutter, they move on till they come to the card, and
here they wheel round each edge of the card and meet

;o6

NINETEENTH CENTURY.

PT. III.

behind it. Those which meet in the middle of the shadow
have each travelled exactly the same distance with the same
number of waves, so they meet as in Fig. 48, and a strong
undulation is produced, causing a band of light. But on
either side of the exact middle the rays will not have tra-
velled exactly the same distance, but one will have made
half a wave more than the other, so they will meet as in Fig.
49, and destroy each other, causing a band of darkness.
Outside these again the ray which has come the longer dis-

FlG. 48.

Fig. 49,

Diagrams illustrating the Interference of Waves.

In Fig. 48 the waves, c d, meet in the same phase, and produce strong undulations.
In Fig. 49 the waves, c d, meet in the opposite phase, and' interfere with each
other.

tance has had time to make up another half-wave, so it meets
the other ray as a friend again, and both of them rising
together, a strong wave and a light band is the result. In
this way they go on, first helping and then interfering with
each other, and thus making alternate bands of light and
darkness across the shadow. For this reason Young called
his discovery the * Interference of light*

CH. XXXII. COLOURS CAUSED BY INTERFERENCE, 307

If this experiment is made with light of one colour only,
as, for example, with light which has been passed through
red glass, and so is composed only of red rays, then the
bands are simply dark and light. But if sunlight is used
another curious effect is seen, namely, the bands are faintly
tinged with the colours of the rainbow \ and this too Young
showed to be beautifully explained by the Undulatory Theory.
It was stated at p. 177 that the colour of the light which
reaches our eye depends upon the rapidity of the vibrations
of the ether, just as the sound of a note upon our ear
depends upon the rapidity of the vibrations of the air.
Consequently the waves of the prismatic colours are of
different lengths, so that when the two rays of light meet
behind the card the waves of the various colours do not
all arrive together. For example, those waves which cause
us to see the colour violet are much shorter and more
rapid than those which cause us to see red. Therefore,
when the red waves meet each other as friends (as in
Fig. 48), and make a strong vibration, the violet ones will
meet each other as foes (as in Fig. 49), and interfere with
each other ; and so we shall see a bright red stripe made by
the strong red wave, while the violet waves will be destroyed
A little farther on the violet waves will meet as friends, and
then we see a violet streak, while the red ones will in their
turn be destroyed.

Colours on the Soap-bubble. — The beautiful colours of
the soap-bubble are caused in this way, and an explanation
of them will help you to picture to yourself this effect of the
interference of light. If you have ever blown a well- shaped
soap-bubble, and watched it settle down quietly where there
is no wind to disturb it, you cannot fail to have noticed the
colours which appear upon it. If the bubble is very perfect

3o8

NINETEENTH CENTURY.

PT. III.

these colours arrange themselves in rings, beginning with a
dark spot at the top of the bubble and forming alternate
bands of blue, yellow, orange, and red, which grow fainter
and fainter down the sides of the bubble till they dis-
appear. The reason of these colours is that, when the
sunlight falls on the thin film of the bubble, a little of the
light is reflected straight back to the eye from the surface <7,
Fig. 50 j but most of it passes on to the second surface ^,
and there again some is reflected, so that two sets of waves
are constantly reaching the eye, one from a and one from b.
These two sets meet before they come to our eye, and we
have just seen (p. 306) that it depends entirely how they
meet whether we see light or darkness.

Suppose the film is just thick enough for the two rays to

Fig. so.

^y^

Reflection of Light from the two surfaces of a Soap-bubble.'

R, Ray of light, part of which is reflected from the surface a, and part from the
inner surface, b, to the eye.

meet when the red waves of each are 7-isi7ig ; we shall then
have a full red wave upon our eye. But in that case, as the

' The film of a soap-bubble is really only the thickness of a fine
line even in the thickest part ; but it was necessary to exaggerate the
two surfaces in the diagram to show the passage of the ray of light.

CH. XXXII. MALUS ON POLARIZATION. 309

violet waves are a different length, they will not have met as
friends, but as foes, one up and the other down, and will
destroy each other ; and so will the waves of all the other
colours, because they are not of the same length as the red
waves. Therefore the only impression on our eye will be
that of red. But the bubble is always growing gradually
thicker down its sides because the soapy liquid is creeping
downwards. So a little lower down the red waves from the
two surfaces « and b will no longer fit each other, but will
meet unevenly and the red colour v/ill be destroyed. It will
now be the turn of the violet rays to combine and make a
strong wave to our eye \ a little lower down it will be the
turn of the green waves, then of the yellow, and then the
film will be thick enough for the red wa^es to come together
again, and so it will go on ; each colour in its turn will pro-
duce a strong wave, while all the others are quenched, until
the film is too thick for the effect to be produced.

This is a very rough idea of the way in which the Undu-
latory Theory explains the colours which we see in shadows
and in the soap-bubble. When you study the subject of
light you will see how very complicated these wave move-
ments really are ; but without special knowledge you cannot
understand more than I have given you here. The colours
on mother-of-pearl, on a duck's neck, on' the transparent
wings of insects, and even on the scum floating on a pond,
are all produced by the interference of light, and we owe
the discovery of this simple and beautiful explanation to
Dr. Thomas Young.

Malus discovers the Polarization of Light by Reflection,
1808. — The next step in the science of light was made by
Etienne Louis Malus, a young French engineer officer, who
was born in 1775, and died in 181 2, when he was only

3IO NINETEENTH CENTURY. pt. hi.

thirty- seven years of age. He was a most accomplished
mathematician, and if he had lived longer would probably
have been one of the most celebrated men of our century.

You will remember that in 1669 a Danish physician
named Bartholinus discovered that a ray of light is split
into two rays in passing through Iceland spar in any direc-
tion except along the axis of the crystal ; and that Huyghens
explained this by saying that the crystal was more elastic in
one direction than in another, so that the waves moved at
different rates through it (see p. 180). To understand
Malus's discovery you must also remember that one of
these divided rays, if it falls upon a second crystal in the
same manner as the first, goes on its way as a single ray,
but if the second crystal is turned round a little the ray splits
up again into two rays, one much blighter than the other.

In the year 1808, M. Malus was standing at his study
window in the Rue d'Enfer, in Paris, looking through a
prism of Iceland spar at the sunlight reflected from the
windows of the Luxembourg Palace, which stood opposite.
All at once he observed to his surprise that he saw only one
image through the prism instead of two. Turning his prism
a little, he got the two images again, but one was much
brighter than the other, and when he turned the crystal a
little farther the other image disappeared, and he had only
one again. In fact, the light which was reflected from the
window at one particular angle (56° 45') behaved just like
one of the divided rays which has come out of a crystal, and
not like an ordinary ray which comes from the sun.

This remarkable peculiarity puzzled Malus greatly, and
led him to make a great many experiments, by which he dis-
covered that, whenever light is reflected from glass at this
particular angle of 56° 45', it has the peculiar characters of a

CH. XXXII. THE POLARIZATION OF LIGHT. 311

divided ray which has passed through Iceland spar. Light
reflected from other substances is also divided up in this
way, only the angle at which this change takes place is dif-
ferent for each different substance. Malus was the first to
call this peculiar tf^Qct polarization, and light which behaves
in this way has since been always called ' polarized light.'

His discovery led to a completely new study, for people
had almost forgotten the experiments which had been made
by Huyghens more than 100 years before j but this novel and
curious fact attracted attention, and the subject was taken up
again. Malus did not live to explain the matter ; he found
out many remarkable facts about it, but it was Young and
the French philosopher Fresnel who really worked out the
theory of the polarization of light.

Polarization of Light explained by Young and Fresnel.
1816. — Augustin Fresnel, the contemporary and friend of
Thomas Young, was bom at Broglie, in France, in 1788.
He was a delicate backward boy, who disliked books, but
loved practical experiments, and he followed his tastes by
becoming an engineer. Being a Royalist, however, he was
harshly treated by the Emperor Napoleon I., and he retired
to Normandy to devote himself to science. He died of
consumption in 1827.

It is very difficult to decide whether Young or Fresnel
was the first to point out how certain peculiar vibrations of
the ether explain the polarization of light. But fortunately
this need not trouble us, for the men themselves were not
anxious to dispute about their claims. Young's discoveries
were very coldly received in England, for very few men un-
derstood them j and unfortunately Lord Brougham wrote
many severe articles against them in the ' Edinburgh Review,'
which made people think they were only foolish specula-

312 NINETEENTH CENTURY. pt. hi.

tions. But in France two men, Fresnel and his friend M.
Arago, understood and valued Young's labours as soon as
they heard of them, and from that time the three men helped
each other in every way without the least jealousy as to who
should have the credit of the work.

Fresnel had puzzled out the question of the * Interference
of Light' before he heard that Young had done so too; and
it happened that while Fresnel and Arago were one day
making experiments upon the way in which waves of light
interfere with each other, they found that the ordinary and
extraordinary rays coming out of crystal and Iceland spar
would not interfe7'e with or quench each other, as two ordi-
nary rays do. (See p. 306.) This led Fresnel to suspect that
the waves in the two rays must move in a different manner.
He wrote this to Dr. Young, and found that he also had the
same idea, and this led to a number of experiments, by
which they proved at last that the waves in a natural ray of
light do not move merely up and down like waves in a pond,
but also from side to side ; and that when light is polarised
this complex vibration is destroyed and the waves of each
separate ray move only in one direction.

To understand this, take a piece of string, and, fastening
one end to the wall, hold the other end in your hand. If you
now move your hand up and down, you will make waves in
the string which will point up to the ceiling and down to the
ground, making what are called vertical vibrations (a. Fig. 51).
Stop this movement, and then move your hand from side to
side ; the waves will now point from wall to wall in horizon-
tal vibrations (b, Fig. 51). If you then move your hand so
that it points to the ceiling to your right, and the floor to
your left, you get waves between the two others, and so you
can go on varying the position of the waves in all directions ;

CH. XXXII. VERTICAL ^ HORIZONTAL VIBRATIONS. 313

or, in scientific language, you cause the string to vibrate in
a different plane.

Now Young and Fresnel proved that a natural ray of
light is composed of all these different waves moving at
the same time, some up and down, some from side to
side, and some between the two. But when the light
passes through a piece of Iceland spar, there are two and
only two ways in which the waves can move : one up and
down— and along this path one ray of light goes ; the
other from side to side — and along this the other ray goes,
and so they become divided.

You can imitate this by passing your string through a
card- with a straight slit in it. Place the card upright, as
at A, Fig. 51, and it is clear that the waves will be up

fc* Diagram illustrating the passage of Waves of Light through a Crystal.

A, Waves moving in a vertical plane. B, Waves moving in a horizontal plane.

and down ; place it sideways, as at B, ^nd the waves will
be from side to side. These two positions of the card
imitate the two paths of a ray of light through a crystal,
and they show how the difference in the peculiarities of
the divided rays is caused by their moving in a different
plane.

We cannot follow this out more completely in a history,
15

314 NINETEENTH CENTURY. pt. hi.

for the polarization of light is a very difficult subject ; but
this was the first step made in it. Fresnel afterwards
worked out accurately why, when light is reflected at a cer-
tain angle, the vibrations are all made to move in one plane,
and so the light is polarized, as Malus had found it to be
from the surface of the Luxembourg windows. He also
showed how in some crystals, as in quartz crystals, the waves
are made to act upon each other, so that, instead of moving
to and fro, they wind round and round like the wire of a
corkscrew. These and many other experiments, as for ex-
ample, those upon the beautiful colours caused by polariza-
tion, were carried much farther by the eminent French
chemist, M. Biot (born 1774, died 1862), and by Sir David
Brewster (bom 1784, died 1868), but they are too long and
difficult to be explained here. As I said at the beginning
of this chapter, the ' Theory of Light ' requires a special
study, and if you have understood something of the move-
ment of the supposed ether waves — how they can interfere
with each other and produce light or darkness, how they
produce coloured rings in the soap-bubble, and how their
vibrations are altered in passing through a crystal or in re-
flection at certain angles — ^you have learnt as much as can be
easily grasped of the discoveries of Young and Fresnel.

Chief Works consulted. — Young's * Lectures on Natural Philosophy,'
1845; Peacock's 'Life and Works of Young;' Arago's *Eloge of
Fresnel;' Herschel's 'Lectures on Familiar Subjects ; ' Tyndall, 'On
Light ; ' Spottiswoode's ' Polarization of Light ; ' Wliewell's * Inductive
Sciences ; ' ' Encyclopaedia Britannica ' — Sixth Dissertation.

cii. xxxiir. SPECTRUM ANALYSIS, 315

CHAPTER XXXIIL

SCIENCE OF THE NINETEENTH CENTURY (CONTINUED).

History of Spectrum Analysis — Discovery of Heat-rays by Sir W,
Herschel — And of Chemical Rays by Ritter of Jena — Photography
first suggested by Davy and Wedgwood — Carried out by Daguerre
and Talbot — Dark Lines in the Spectrum first observed by Wollaston
— Mapped by Fraunhofer — Life of Fraunhofer — He discovers that
the Dark Lines are different in Sun-light and Star-light — Experi-
ments on the Spectrum of different Flames — Four new Metals dis-
covered by Spectrum Analysis — Bunsen and Kirchhoff explain the
Dark Lines in the Solar Spectrum — Metals in the Atmosphere of
the Sun — Huggins and Miller examine the Stars and Nebulae by
Spectrum Analysis.

History of Spectrum Analysis, 1800-1861. — We now

come to the history of Spectrum analysis^ or the study of
the various coloured bands produced by different kinds of
light when seen through a prism. This is certainly one of
the most wonderful discoveries of our century, and though
its history is difficult, partly because it belongs to our own
time and is going on even now, yet we may learn something
about it. The first step was made, as you will remember,
when Newton discovered that white light is composed of
different coloured rays, but even he little suspected what
histories those rays could be made to tell.

Discovery of Heat-rays by Sir William Herschel, 1800.
— One of the first facts which was learnt in this century about
the spectrum was, that the coloured band which is seen
when a ray of white light is passed through a prism does not

3i6 NINETEENTH CENTURY. pt. hi.

give us the whole of the dispersed ray ; for there are many-
invisible rays at both ends of the coloured part which are
very active, though we cannot see them.

It had alway^s been thought that the hottest rays must be
those, such as the yellow ones, which give the most light, and
in the year 1800 Sir William Herschel, wishing to try this,
took a thermometer and passed it gradually from one end
to the other of the coloured band. The result was curious.
He began at the violet end of the spectrum (Plate I. No. i,
p. 320), and, as he expected, the thermometer rose higher
and higher as he approached the yellow part ; but to his
surprise it did not stop here. When he passed on through
the yellow into the red, the heat still increased, and even
became more intense as he passed out of the coloured band
altogether into the darkness beyond. By this experiment he
found that the heat-rays extend for some distance beyond
the red colour, and that they are strongest in that part where
no light is to be seen.

Discovery of Chemical Rays by Hitter, 1801. — Soon
after Sir William Herschel had discovered the dark heat-
rays, a still more remarkable fact was brought to light about
the violet end of the spectrum. The Danish chemist Scheele,
who you will remember as one of the discoverers of oxygen
(see p. 232), had once remarked that nitrate of silver will
turn black if the violet rays of a spectrum are thrown upon
it. In 1 80 1, Professor Ritter, of Jena, was repeating this
experiment, and he found that the black patches appeared
slightly on those parts of the paper where the violet rays
fell, but very strongly indeed beyond those rays where the
spectrum was quite dark. So that at this end also there are
invisible rays, and these have the extraordinary power of de-
composing or breaking up nitrate of silver, and some other

CH. XXXIII. PHOTOGRAPHY. 317

substances, so as to leave distinct marks upon anything
touched by them.

Photography. — You will see at once that this is the
secret of Photography. In 1802, Sir Humphry Davy and
Dr. Thomas Wedgw^ood suggested that pictures might be
taken in this way by the rays of the sun acting upon chloride
of silver, and they even succeeded in making some. But
they could not prevent them from fading away again, and
it was not until 1839 that a Frenchman named Daguerre
learnt how to fix the pictures so that they would remain, and
Mr. Fox Talbot afterwards improved the process. We can-
not enter here into a complete account of photography, but
you may form some idea of how the rays of light produce a
picture.

When you go to have your photograph taken, the glass
plate which is to receive your picture has been bathed in
nitrate of silver, with some other chemicals. When you
stand in front of it and it is uncovered, a luminous image
of your face or body, which has been brought to a focus
on the lens of the camera, falls upon the plate, and the che-
mical rays (which are chiefly those beyond the violet end of
the spectrum) decompose the nitrate of silver. You can
see nothing when the plate is taken out of the box in which
it was placed, but by pouring some more chemicals called
protosulphite of iron and pyrogallic acid upon it, the parts
which the light has touched all start out in different shades,
exactly in proportion as the chemical waves of light have
fallen upon it strongly or feebly. It will be exactly the
opposite to your real appearance, because where most light
has fallen, there the chemicals will be most decomposed and
will leave the blackest tints.

Another fluid called hyposulphite of sodium is now

3i8 NINETEENTH CENTURY. PT. ill.

poured upon the plate to melt away any nitrate of silver
which remains, so that when the sun next falls upon it it
may not blacken the rest of the plate and destroy the
picture. Then the glass plate is again placed in the sun
with properly prepared paper under it ; and now the shades
are reversed. Under the dark parts of the plate the sun
will act feebly on the paper, and produce light patches,
while through the light parts it will act strongly and produce
shadows. And in this way the lights and shades of your
image will appear in their right places on the paper. All
this work is done by the chemical rays which are chiefly at
and beyond the violet end of the spectrum, and this explains
why bright red and yello\y objects come out dark in a photo-
graph, because these colours contain so i<s.y{ chemical rays,
while the darkest blue and violet come out nearly white,
because they act strongly upon the nitrate of silver.

WoUaston first observes the Dark Lines in the Spectrum,
1802. — In the same year that Ritter discovered the chemi-
cal rays at the dark end of the spectrum which have given
us the whole art of photography, Dr. WoUaston, one of
our most celebrated chemists (born 1766, died 1828), first
saw the dark lines in the spectrum which have enabled us to
discover the actual materials which exist in the sun and
stars. Dr. WoUaston, who made many good experiments
on light, was one day examining ordinary daylight through
a prism, and instead of letting in the light by a round hole
in the shutter as Newton had done, he made only a very thin
slit, so that the colours of the spectrum were prevented from
overlapping each other, as they had done in Newton's expe-
riment. The result was that seven dark upright lines or
spaces appeared in the band of colour, which seemed to show
that no light fell on those parts. WoUaston did notliing more

CH. XXXIII. FRAUNHOFERS DISCOVERIES. 319

than point out the existence of these Hnes j but in 181 4
Fraunhofer, a German optician, who had heard nothing of
Wollaston's experiment, discovered them over again inde-
pendently, and learnt more about them.

Fraunhofer, 1787-1826.— Joseph Fraunhofer, the son
of a glazier, was born in 1787, at Straubing, in Bavaria.
Being left an orphan when quite young, he was apprenticed
to a glass manufacturer, who kept him hard at work all day.
But he longed so much for knowledge that he borrowed
some old books and spent his nights in learning. In the
year 1801 the house in which he lived fell down one night
and killed all the people in it except young Fraunhofer,
and his cries being heard by the people outside, they set to
work to try and release him. It happened that Maximilian
Joseph, Elector of Bavaria, came to see the accident, and
he encouraged the workmen so much, that in four hours the
young man was dug out, wounded, but alive. The Elector
was so much interested in this narrow escape, that he gave
Fraunhofer eighteen ducats, and the lad used the money to
buy himself off from his apprenticeship in order to have
some free time for study. After this he lived by polishing
lenses, and he worked so well that he soon became the
master of a business, and was able to spend his spare time
in the study of Physics and Astronomy, which he loved pas-
sionately. Finally he became manager of the physical
laboratory of an academy in the town of Benedictbaiern,
near Munich. "

Fraunhofer's Discoveries about the Spectrum, 1814. —
From having been constantly at work as an optician, Fraun-
hofer had been led to study the subject of light, and among
other experiments he repeated those of Newton; and it hap-
pened that he too used a narrow slit, as Wollaston had done.

320 NINErEENTH CENTURY. pt. hi.

Thus he also noticed the black lines which divided the
colours, and by making his slit very narrow and using prisms
of very pure glass he discovered in a ray of sunlight no less
than 576 of these black lines. Plate I., No. 2, gives a few of
the principal of these, to which he put letters, and which have
ever since been called ' Fraunhofer's lines.' As none of these
lines appear when the light of a candle or lamp is passed
through a prism, Fraunhofer concluded that sunlight must
be defective, and some of its coloured rays must be missing.
For, as numberless waves of coloured light are passing
tlirough the slit and the prism spreads them out so that
each set of waves makes an upright image of the slit on the
spectrum, if any waves were missing there would be a dark
image of the slit instead of a coloured one.

By far the best way of understanding this is to see it for
yourself Sir John Herschel says that a little inexpensive
instrument may be easily made with a hollow tube of metal,
blackened inside, a prism fixed in it, and a metal plate with
a narrow slit fastened across the end of the tube. I have
not been able to find so simple an instrument as this ; the
cheapest sold by Mr. Browning, the famous spectroscope
maker, in the Strand, costs twenty-two shillings, and with
this you may see the black lines clearly when you turn
it to the sun. But if this is not to be had, you may gain
some idea of the principle of the dark lines by the following
illustration. Colour a strip of paper exactly like the con-
tinuous spectrum, No. i, Plate I., and then cut it across into
very narrow strips and place them in order side by side on a
dark ground ; each strip will represent an image of the slit,
and the whole will be a continuous spectrum as before. But
now suppose one set of waves to be wanting ; take out one
of your strips and you will have a dark space. This repre-

CH. XXXIII. SPECTRA OF DIFFERENT FLAMES. 321

sents one of the black lines in the spectrum where a dark
image of the slit is thrown, and if you take out those which
correspond to the lines in the sun spectrum No. 2, you will
have an illustration of ' Fraunhofer's lines.'

Fraunhofer measured these black lines with the greatest
care, and he found that in every ray of sunlight they came
exactly in the same places. Then he tried the light of
the moon and Venus ; still the black lines were the same,
for these planets, as you know, only shine by the light of
the sun. But, when he turned his telescope to the stars
and caught their light, he found a difference. There were
dark lines in the star- spectrum, but they were not all in
the same place as those in the sun-spectrum, as you will
see if you compare No. 2, Plate I., with the star-spectrum,
No. 5, in which the lines seen on the right-hand side of the
solar spectrum are entirely wanting.

Fraunhofer, therefore, argued in this way ; If the black
spaces were caused by some of the waves being stopped in
coming through our own atmosphere^ they would be the
same in any spectrum wherever the light came from. But
as these dark spaces are different in the starlight from what
they are in the sunlight, there must be some real difference
between the light of the sun and the light of the stars before it
comes to us. This was the first step in the study of the
heavenly bodies by means of spectrum analysis.

Experiments on the Spectra of different Flames, 1822. —
For more than forty-five years these black lines remained a
complete puzzle to all who studied the spectrum, but in the
meantime Sir John Herschel, Mr. Fox Talbot, Sir David
Brewster, and others, had made many valuable experiments
upon the colours produced by different burning lights. You
know already that it is possible to make coloured flames by

322 NINETEENTH CENTURY. PT. iii.

burning certain substances. For instance, if you put com-
mon salt in a spirit-flame, it will burn with a yellow colour,
while a substance called nitrate of strontium will give a
brilliant red flame, and is used in making red fire for the
theatres. Many other metals and earths, however, tinge the
flame so slightly that you cannot see the colour, and it is
only by passing the light through a prism that you can
detect it.

It had long been known that light from white-hot solids
when thrown on a prism produces a continuous spectrum,
that is, a coloured band unbroken by any dark lines. A
white-hot poker, for example, will give the spectrum No. i,
Plate I., and so will burning paraffin, because it contains
solid atoms of carbon. But burning gases or vapours do not
give a continuous band of colour, they only produce a few
bright lines, such as those in Nos. 3 and 4. You can s'ee
this by looking at an ordinary gas flame through Browning's
little spectroscope.

Now there is a remarkable peculiarity about these bright
lines formed by gases or vapours, namely that they are
diffe7-ent for the gas or vapour of every different substance.
Thus, if you burn any substance containing sodium, a bright
yellow stripe will appear as in No. 3 ; while hydrogen will
give one red, one blue, and one violet stripe, as in No. 4.
This test is so true and delicate that the eighteen-millionth
part of a grain of sodium will give the yellow line ; nor does
it matter if you bum many substances together, for the
vapour of each one will give its own lines without inteifering
luith the others.

It was Sir John Herschel in 1822 who first suggested
that by burning substances in a flame, and marking the bright
lines which they produced, it would be possible to detect the

CH. xxxili. BUNSEN AND KIRCHHOFF. 323

most minute quantities of any metal or earth which they con-
tained, and Mr. Fox Talbot carried out this suggestion in
1834. By this means in the course of time spectroscopists,
or men who made the spectrum their study, were able to
map out accurately the coloured lines of every known sub-
stance ; and what is still more wonderful, new metals were
actually discovered by the new lines they threw on the dark
band. The first of these two new metals, called CcEsium
and Rubidium^ were discovered by Bunsen and Kirchhoif ;
the third, called Thallium, which throws a beautiful green
line, was found by Mr. Crookes ; and the fourth, called
Iridium, by Richter and Reich. Thus you see spectrum
analysis gives us an entirely new and sure way of analysing,
or discovering the different elements in any substance.

Bunsen and Kirchhoff explain the Dark Lines in the
Sun Spectrum, 1861. — But all this time no one could solve
the question of the black lines in the solar spectrum. Sir
David Brewster came very near to it once, but just failed to
hit upon the truth. ^ At last, in 186 1, only fourteen years
ago, Bunsen and Kirchhoff, two celebrated professors of
chemistry and physics at Heidelberg, discovered the secret.

These two men had been making a long set of careful
experiments upon all the different substances of our globe,
burning them and examining their gases one by one, and
marking the bright lines of each upon the spectrum. In
doing this they- did not use one prism only as Fraunhofer
had done, but four (see Fig. 52, p. 324), so arranged that
the light coming in through a slit at the beginning of the

^ Sir William Thomson states in his address to the British Asso-
ciation in 1 87 1, that Professor Stokes gave the true explanation of
these lines in his lectures at Cambridge in 1 85 1, although he did not
publish anything about it, and his idea was not generally known.

324 NINETEENTH CENTURY. rr. in.

tube A, was spread out more and more through each prism
as it passed, and fell in a spectrum on the object glass, c, of
the telescope b, through which they examined it. They soon
found that in order to mark the exact position of the bright
lines of each gas upon the spectrum, they wanted some
fixed measure, and it occurred to them that the black lines
of the solar spectrum, which never change, would make a
good scale with which to compare all the others. So they
arranged their spectroscope in such a manner that one-half
of the slit was lighted by the sun and the other half by the

Fig. 52.

KirchhofF's Spectroscope (Roscoe).

flame of a gas. In this way No. 2, Plate I., would appear
above, and No. 3, for example, immediately below it.

While doing this they could not help remarking that the
bright yellow line of the sodium spectrum. No. 3, was exactly
in the same position as the black line, d, in the solar spec-
trum ; * and Kirchhoff found that when he passed a faint
ray of sunlight through a flame of sodium (so as to make

^ These lines are really double when seen in a powerful spectro-
scope, but they appear single in a small instrument.

CH. XXXIII. THE SOLAR SPECTRUM. 325

the two spectra, 2 and 3, cover each other), the yellow line
exactly filled up the black line with its light. He now
wished to see how bright he could make the solar spectrum
without overpowering the light of the sodium, so he let the
full sunshine pass through the sodium flame. To his great
astonishment he saw the black line at d start out more
strongly than ever. The sodium flame had revenged itself
for being overpowered by absorbing some of the yellow light of
the Sim /

This suggested to him the idea that the black line d must
be caused by the white light from the sun passing through
sodium vapour before it reaches us. There was a very simple
way of proving whether this were so ; for burning solids, you
remember, give a continuous spectrum (i, Plate I.), there-
fore, if he could produce a dark line by passing the light of
a burning solid through sodium vapour, he would imitate
one of the defects in sunlight. So he burned a lime-light,
and when he had the continuous coloured band in his
spectroscope, he burned a sodium flame between the lime-
light and the prism. The experiment was quite successful ;
the dark space, d, started out upon the spectrum, and thus
he proved beyond doubt that burning sodium vapour absorbs
in white light exactly those rays which it gives out itself when
burning.

He repeated the experiment with other burning metals,
such as potassium and strontium, and always with the
same result. Each burning gas absorbed in the white light
exactly those rays which it gave out itself when burning.

The black lines on the solar spectrum were now explained,
for each one of them must imply that some particular ray of
sunlight has been absorbed by a gas between the sun and
us, and it must have been absorbed near the sun, as Fraun-

326 NINETEENTH CENTURY. n. ni.

hofer had pointed out, because the lines are different in
Hght which comes from the stars, showing that in that case
it has passed through other kinds of gases. Therefore
Kirchhoff concluded that round the solid or liquid body of
the sun, which gives out white light, and would of itself pro-
duce a continuous spectrum, there must be an atmosphere of
gases of different kinds, which absorb or destroy particular
rays of light, and prevent them reaching us.

If this is the case, it is clear that we can tell from the
lines in the spectrum what gases and vapours there are in
this solar atmosphere. For example, there must be sodium
which cuts off the rays which ought to come to d, and there
must be also iron, magnesium, calcium, chromium, potas-
sium, rubidium, nickel, barium, lead, copper, zinc, strontium,
cadmium, cobalt, uranium, cerium, vanadium, palladium,
aluminium, titanium, and hydrogen, for the bright Hues of
all these metals are replaced by dark lines in the solar
spectrum, showing that the white light from the body of the
sun must have passed through their gases.

Dr. Huggins and Dr. Miller examine the Stars by
Spectrum Analysis, 1862.— Only a few months after Kirch-
hoff had proved that the black lines in the solar spectrum
reveal to us what elements exist as gases around the sun,
two Enghsh chemists. Dr. Miller, who died a few years ago,
and Dr. Huggins, who is still living, began to try the same
experiments with the other heavenly bodies, and the study
has since been carried still farther by Mr. Lockyer.

Their instruments were now much more perfect than
those which Fraunhofer had used, and they were able to see
the effects of our own atmosphere upon sunlight, for when
the sun is setting and its light has to pass through a long
layer of air before it reaches us, faint lines appear on the

CH. xxxiii. GASEOUS NEBULA. 327

spectrum, because some light is absorbed by the vapours in
our atmosphere. Now, when Miller and Huggins examined
the light which comes from Jupiter, they found three or four
lines like those caused by our atmosphere, showing that
Jupiter must have an atmosphere partly, but not entirely like
ours. Mars and Saturn also both showed these atmospheric
lines, and so did Saturn's rings, proving that a similar atmo-
sphere must spread over them also. But our moon gave none
of them, and this agreed with other evidence in showing that
the moon has no atmosphere.

They next passed on to examine the light of the stars, and
this was by no means an easy task, because the stars are so far
off that their light is very faint and difficult to catch. Never-
theless they proved that round one star, called Aldebaran
(No. 5, Plate I.), there must bean atmosphere of hydrogen,
sodium, magnesium, calcium, iron, tellurium, antimony, bis-
muth, and mercury, and you will notice that the last four of
these are not found in the sun. In the light of the star
Betelgeux, in the constellation Orion, and in another star,
called /3 Pegasi, no hydrogen is found, but it is found in all
the other stars, together with many other substances. In
some of the stars there are besides, lines which are not found
by the burning gas of any known substances on our earth.

Dr. Huggins proves that some Nebulae are Gaseous,
1864. — And now we come to a very interesting experiment.
You will remember that astronomers doubted Sir W.
Herschel when he suggested (p. 275) that some of the
nebulae are not made of tiny stars, but of gas which is
forming into stars. In 1864 Dr. Huggins began to examine
these nebulae with the spectroscope, and he found that they
did not give a band of colour with dark lines upon it as the
stars do, but a feiu faint lines on a dark ground^ exactly as

328 NINETEENTH CENTURY. pt. hi.

gases do which we bum here on earth. If you compare the
spectrum of sodium (No. 3), or of hydrogen (No. 4), with the
nebula spectrum (N0.6), you will see at once that the nebula
spectrum is made by a gas, and so the truth of Sir W.
Herschel's idea was proved, and there can be now no doubt
that some of the nebulae are composed of gaseous matter ;
chiefly, so far as we can learn, of nitrogen and hydrogen.

Mr. Alexander Herschel examines the Spectrum of
Falling Stars. — I have said that it was difficult to examine
the spectrum of the stars and nebulae, but something which
to an ordinary observer seems still more wonderful has been
lately done. Mr. Alexander Herschel has actually caught the
light oi falling stars in the spectroscope, and in this way has
discovered that some of them give a continuous spectrum,
showing that they are solid bodies, while others give a gas
spectrum, on which are the bright lines of potassium, sulphur,
and phosphorus, but chiefly of sodium.

Such wonderful facts as thes.e about far-distant suns and
sun-matter, we have learnt, and are still learning by means
of spectrum analysis. The whole study was only begun
fifty years ago, and it is in the works of living men that
you must look for the details of its history. But though
many eminent names are connected with it, those of Fraun-
hofer and Kirchhoff should always be remembered as the
chief founders of the science.

Chief Works consulted. — Roscoe's * Spectrum Analysis ; ' ' Edin-
burgh Review,' vol. cxvi. ; * Philosophical Magazine,' i860; Proctor,

• The Sun ; ' Tyndall's * Lectures on Light ; ' * Half-hours with Modern
Scientists;' Kirchhoff's 'Researches on the Solar Spectrum,' 1862;

* Encyclopaedia Britannica, ' art. * Optics ; ' Ganot's ' Physics ; ' Wol-
laston, * On Dispersion ' — * Phil. Trans.' 1802; Lockyer, ' The Spec-
troscope.'

cii. XXXIV. HEAT. 329

CHAPTER XXXIV.

SCIENCE OF THE NINETEENH CENTURY (CONTINUED).

Early Theories about Heat— Count Rumford shows that Heat can be
produced by Friction — He makes Water boil by boring a Cannon —
Davy makes two pieces of Ice melt by Friction — His conclusion
about Heat —How * Latent Heat ' is explained on the theory that
Heat is a kind of Motion — Dr. Mayer suggests the Determination of
the Mechanical Equivalent of Heat — Dr. Joule's Experiments on
the conversion of Motion into Heat — Dr. Him's Experiments on the
conversion of Heat into Motion — Proof of the Indestructibility of
Force, and Conservation of Energy'.

Early Theories about Heat.— From Light we will now
pass on to Heat, and in this chapter I hope to show you how
the philosophers of this century have discovered what heat is.
The subject in itself is so vast that a mere sketch of all the
men who have worked at it and their chief experiments
would fill a volume of this size, and you must clearly under-
stand that we can only select those examples which will best
enable you to comprehend the nature of heat, and how it
has been determined.

Have you ever asked yourself what heat is, or why
the mercury in a thermometer rises when it is put into
hot water? The old philosophers considered heat to be
a fluid, which passed out of substances when they were
too full of it, and which, entering the mercury of the ther-
mometer, swelled it out and made it rise. This was the
general idea about heat up to the end of the eighteenth

330 NINETEENTH CENTURY. pt. in.

century, although Lord Bacon, more than two hundred
years before, had suggested that it was not a fluid but a
movement, and the philosopher Locke, in the seventeenth
century, and Laplace in 1780, gave the same explanation.

Still most scientific men looked upon heat as a fluid,
which they called caloric, until, in the year 1798, Count Rum-
ford first showed by experiment that it is probably a kind of
motion. In following strict chronological order, this dis-
covery ought to have been mentioned at the end of the
eighteenth century, but it belongs so intimately to the modern
theory that it comes more naturally in this place.

Count Rumford shows that Heat can be produced by
Friction, 1798. — Benjamin Thompson, afterwards Count
Rumford, was born in the United States in 1753. He
spent his early life fighting in the English army against the
Americans, in the War of Independence, and afterwards
settled at Munich, and became aide-de-camp to the Elector
of Bavaria. In 1798 he came over to England, where he
was one of the founders of our Royal Institution, and finally
he died in Paris in 1844.

Rumford's inquiries into the nature of heat began in
rather a curious way. He was very anxious to make the
poorer people in Bavaria happier and more prosperous, and
to accomplish this he persuaded the Elector of Bavaria in
1790, to forbid anyone to beg in the streets. Those who
could not find work for themselves were taken up and kept
in a kind of workhouse, where they were given good food
and clothing, but were forced to work to pay for their own
support. When this law was first passed, there were no
less than 2,500 beggars to be provided for, and Rumford
was obliged to calculate very closely how he could find
food and clothing, heat and light, for the least money.

CH. XXXI V. COUNT RUMFORD. 331

Accordingly he studied how fire-places could best be built
to prevent coal being wasted, and invented a lamp which
gave a brilliant light, without burning so much oil as other
lamps did. He even went so far as to make a complete
set of experiments on different clothing materials, in order
to see which kept in the most heat. It was in this way,
and especially in using steam for warming and cooking,
that he first began to study the properties of heat, and he
became much interested in the different ways in which it
may be produced.

It happened one day, when he was boring a cannon in
one of the military workshops of Munich, that he noticed
with surprise the great heat produced by the grinding of the
borer against the gun. You can easily make a similar ex-
periment by boring a hole quickly with a gimlet in a piece
of hard wood, and on withdrawing the gimlet you will find
that it is hot enough to burn your hand. Rumford examined
carefully the gun and the chips which fell from it, and found
that they were both hotter than boiling water.

This led him to consider how it could possibly happen,
if heat were a fluid, that the mere rubbing of two metals to-
gether should produce it ; and he tried many experiments to
find out whether the gun, the chips, or the borer had lost
anything in consequence of having given out heat. But he
could not discover that they were changed in any way ; and
moreover, he found that by going on boring he could make
them give out heat as long as he liked, whereas if he
had been drawing a fluid out of the metals it seemed to
him that it ought to come to an end sooner or later.
Then he considered whether the heat could come out of
the air, and to avoid this he repeated the experiment
under water, but still the metals grew hot, and even made

332 NINETEENTH CENTURY. pt. hi.

the water warm, so it was clear they had not drawn any
heat from that fluid.

He now began to suspect that Bacon and Locke might
be right, and that the rubbing together of the two metals
might set their particles vibrating in some peculiar way so
as to cause what we call heat. If this were so, then by great
friction he ought to be able to produce any amount of heat,
and to prove this he tried the following experiment.

He took a large piece of solid brass the shape of a can-
non, and partly scooped out at one end. Into this he fitted
a blunt steel borer, which pressed down upon the brass with
a weight of ten thousand pounds. Then he plunged the
whole into a box holding about a gallon of water, into which
he put a thermometer, and fastening two horses by proper
machinery to the brass cylinder he made them turn it round
and round thirty-two times in a minute, so that the borer
worked its way violently into the brass. Now notice what
happened : When he began the water was at 60° F., but
it soon grew warm with the heat caused by the friction
of the borer against the brass. In one hour it had risen 47°
up to 107° Fahr. ; in two hours it was at 178°, and at the
end of two hours and a half // actually boiled.

' It would be difficult,' writes Rumford, ^ to describe the
surprise and astonishment of the bystanders on seeing so
large a quantity of water heated and actually made to boil
without any fire,' and he adds that he himself was as delighted
as a child at the success of the experiment j and we can
scarcely wonder, for he had proved the grand fact that
^notion can be turned into heat!

Rumford afterwards calculated that the friction caused
by one horse pulling round the cylinder against the borer

CH. xxxiv. SIR HUMPHREY DAVY. 333

was sufficient to raise 26 lbs. of ice-cold water up to the
boiling-point in two hours and a half.

Davy makes Two Pieces of Ice melt by Friction in
a Vacuum, 1799. — Only a few months after Rumford had
made the discovery that heat can be produced by friction,
Sir Humphry Davy, whose history as a chemist you will
read in chapter xxxvi., proved the same thing by a different
experiment. He took two pieces of ice, and by rubbing
them together made them melt without any warmth being
brought near them. In this case, as he said, no one could
think that the heat came out of the ice, for ice holds less
heat than, water ; and in order to be quite sure that it did
not come out of the air, he made a second experiment He
took a small piece of ice and put it in a machine under an
air-pump, by means of which he drew out all the air ; then
he set his machine to work so that it rubbed against the ice,
and in this way he melted the whole lump, without any air
being present.

Heat a Vibration. — From these experiments Davy came
to the conclusion 'that heat is a peculiar motion, probably a
vibration of the corpuscles (that is the little particles) of
bodies, tending to separate them.' Thus for example, when
you put a saucepan full of water on the fire, the quivering
motion which is going on in coals as they burn passes into
the iron of the saucepan, and through it to the water. Im-
mediately all the little particles of which the water is com-
posed are pushed asunder as if they were trying to get away
from each other ; but as they are still held together by the
force of attraction, they vibrate to and fro, struggling more
and more to get free, and it is this motion which causes in
us the feeling of heat when we come in contact with it.
Then, if a thermometer be placed in the water, the vibration

334 NINETEENTH CENTUR V. . pt. hi.

passes on through the glass of the tube into the mercury, and
the particles of mercury are also set in motion, and so the
mercury swells and rises in the tube.

The cause of Latent Heat explained. — And now, if
you will look back for a moment to chapter xxviii., and
read again about the ' latent heat ' which puzzled Dr. Black
so much, you will see how beautifully it can be explained
by this theory that heat is a kind of motion. You will
remember that, however much heat he put under a piece
of ice he found that the temperature of the water would
not increase above o° Cent, so long as a morsel of ice
remained unmeltedj and again, that boiling water never
grew hotter than ioo° Cent, while it was being turned into
steam. Now if we look upon heat as a vibration, we can
understand that the motion which is sent into ice from the
fire below, will all be employed in overcoming the force of
attraction and separating the particles of ice so as to turn
the solid into a fluid, and it will only be when the last
particles are free that there will be any movement to spare
so as to produce the quivering motion of heat. Then if
you go on heating the water still more, the struggling move-
ment will continue between the force of attraction and the
force of motion, and so the water will grow hotter and hotter,
till at last at ioo° Cent, the force of motion wins the battle,
and the little particles fly asunder and float away as steam ;
and from that moment all the extra movement is employed
in forcing asunder particle from particle, till all the water
has passed away in vapour.

It was for this reason that Watt had to use so much
more cold water to cool down steam of ioo° Cent, than
to cool down water of ioo° Cent. ; for in cooling down
steam he had not only to get rid of the quivering motion

CH. XXXIV. DYNAMICAL THEORY OF HEAT. 335

of heat, but of all the extra force which was holding the
particles asunder.

Dr. Joule's Experimeiits on the Conversion of Motion
into Heat, 1849. — It had now been shown that motion
could be turned into heat, and Rumford had even calculated
roughly how much heat was caused by a certain amount of
motion. But when a horse walks round and round you cannot
measure how much strength he gives out, and in order to
prove that motion by itself can produce heat we must
measure exactly how much motion produces a definite
quantity — say 1° Fahr. of heat, and then see if that amount
of heat can be turned back again into motion. This was
done by Dr. Joule, of Manchester, a celebrated physicist,
who is still living.

In 1839 a Frenchman named M. Seguin, and in 1842
a German physician. Dr. Mayer, of Heilbronn, both sug-
gested that by careful experiments it might be found out
how much work must be done to produce a certain quantity
of heat, and Dr. Mayer made many calculations about it. In
1843, without having heard of Dr. Mayer's suggestion. Dr.
Joule began those famous experiments which have formed
the foundation of the dynamical theory of heat, or the theory
of heat produced by motion, and he completed them in 1849.
A description of one of his experiments -wall explain the
results he obtained. He took a weight, a. Fig. 53, which
weighed i lb. and fastened it by strings to the roller,// On
to the wheel, b, of this roller he wound another string which
passed round the roller r, and this roller was attached to a
paddle which was shut into the box of water, c. He next
wound up the string on the roller / so as to draw up the
weight A, and then set it free. Immediately the force of
gravity drew the weight down to the ground, and in doing so

336 NINETEENTH CENTURY. pt. in.

pulled round the wheel b, and consequently the roller which
turned the paddle in the water. When the weight reached
the ground he took out the little pin, /, which fastened the
paddle to the roller, so that he could wind up his apparatus
without disturbing the water and begin again.

Now observe how this measured the motion and the
heat. Every time the weight fell, it turned the paddle, and
so, by agitating the water, added to its heat. The scale, d,
told him exactly how far the weight fell, while the thermo-
meter, t, in the box told him how much hotter the water
grew. At the end of an hour, therefore, he had only to see
how many feet his pound- weight had fallen, and how
many degrees of Fahr. the heat of his water had risen ;
and after allowing for the friction of his machinery and
for the heat lost in the cooling of his vessel, both of which
he ascertained by careful experiments, he could tell how
much motion had been used up in producing the heat. In
this way he found that a weight of i lb. would have to fall
']']2 feet in order to make i lb. of water warmer by i° Fahr.

He next tried the same experiment with oil and with
mercury instead of water, and also measured the heat pro-
duced by rubbing together two plates of iron ; and in every
case he found that a certain amount of work gave a certain
amount of heat and no more. For example, if the weight
in Fig. 53 fell double the distance, the heat of the water was
raised two degrees instead of one, while if it fell only half the
distance, or 386 feet, the water was only raised half a degree.

In this way Dr. Joule established what is called the
mechanical equivalent of heat, namely that the fall of a pound
weight through 772 feet equals the heating of a pound of
water 1° Fahr. And now you must try to foim a clear idea
what this means, and how it proves that heat is altered

CH. XXXIV. CONVERSION OF MOTION INTO HEAT. 337

motion. Looking at the diagram, try to picture to your-
self what would be taking place if the weight was able to
fall the whole 772 feet without stopping. First, a man must
wind up the weight, and in doing this he uses force to over-
come the force of gravitation which is pulling the weight
down to the earth ; so that the machine starts with a certain
stock of force stored up in the weight, and its amount is
called 772 foot-pounds because it has raised a weight of

Joule's Experiment on the Conversion of Motion into Heat (Phil. Trans).

A, Weight. 15, Wheel of the roller, _/"_/ c, Vessel containing water and the paddle.
D, Scale to measure the distance that the weight falls, e, Paddle contained in
the vessel, c. ff. Roller turned by the falling weight, r. Roller turning the
paddle, p. Pin which joins the roller and the paddle, t. Thermometer plunged
in the vessel, c.

I lb. to a height of 772 feet. This stock of force philoso-
phers cslX potential energy ^ or possible energy which may be
called into use at any time. When the man sets the weight
free, it begins to fall, drawn down by the force of gravity,
and the stock of energy is set free. What becomes of it?
It passes by the wheel b into the roller r, and, turning the
paddle in the box, enters the water. If the water were free,
16

338 NINETEENTH CENTURY. pt. iii.

it would pass on into the air and we should lose sight of it ;
but the water is shut in and the force cannot escape, so
now it employs itself in dashing to and fro all the little
particles which make up the water, and producing the effect
we call heat j and as it produces exactly i° Fahr. of heat
by the time the i lb. weight has fallen 772 feet, we say
that 772 foot-pounds of foi'ce equals 1° Fahr, of heat You
might easily prove to yourself in a somewhat unpleasant way
that the force is there ; for if you were to go on turning the
paddle violently for many hours, and there were no means
for the heat to escape, the motion of the particles would be
so violent against the sides of the boiler that it would burst.
Hirn's Experiments on Heat converted into Motion.
— If you have understood this explanation, you will have
some idea of the theory that heat is altered motion \ but to
complete the history we require not only to turn work into
heat, but also to turn heat into work. This had already
been done many years before by a French engineer, M.
Camot, though he did not understand its real significance,
but it has now been most beautifully proved by a long
series of experiments made by M. Hirn, of Colmar, in
Alsace. What M. Hirn practically did was to find out how
much heat can be obtained from a ton of coals, and then to
find out how much work v/as performed in an engine by
that amount of heat. This was by no means a simple task,
for much heat is lost in various ways in passing through the
engine ; and even when he thought he had allowed for all
this, it was found that some of the steam had turned back
into water on its way, and thus used up some of the heat.
At last, however, when all was carefully measured and calcu-
lated, he found that^r every pound of water heated 1° Fahr.^
enough work had been done to raise a weight of i lb. to a

CH. XXXI '/. CONSERVATION OF ENERGY, 339

height of 1"] 2 feet. This, you will notice, was exactly the con-
verse of Joule's experiment, and proved that exactly as much
motion is produced by means of confined heat as there is
heat produced by means of checked motion.

Conservation of Energy. — And thus we arrive at one
of the grandest discoveries of modern science, namely, that
the whole amount of enei'gy, or power of doing work, pos-
sessed by any set of bodies, remains unaltered whatever
transformations it may undergo. It may exist in one of
two forms — either djs> potential or stored-up energy, which is
unseen by us, or as visible enei'gy, when it is actually per-
forming work ; but while it changes from one form to another
its amount never alters. Thus in Joule's experiment the
energy stored up in the weight which had been pulled up
772 feet was gradually transformed, as soon as the weight
was released, into an amount of heat capable of raising the
temperature of a pound of water 1° Fahr. ; while Him
showed, on the other hand, that exactly this amount of heat
can be turned back into enough energy to raise a weight
to the height of 772 feet at which it stood before.

The potential energy, or power of-doing work, remained,
therefore, exactly the same whether it was stored up in the
weight or in the hot water, and reproduced exactly the same
amount of visible energy or actual work. And even though
we know that practically some energy disappears at every
part of a machine when it is at work, yet this is not lost ; for
it turns into heat wherever it disappears as motion. If you
grease the wheels of a machine, you will detect this heat
beginning to do work again by turning the solid grease into
a liquid.

By whatever means, therefore, heat is turned into motion,
or motion into heat, the energy which causes them both

340 NINETEENTH CENTURY. pt. ill

remains the same, and this is one out of many proofs that
force cannot be destroyed, but is only lost in one form to re-
appear in another.

Other Experiments on Heat. — Although the experiments
and calculations which have proved heat to be a kind of
motion are some of the most interesting which have been
made of late years, yet they are by no means the only ones.
In 1811 Sir John Leslie carried on a most interesting series
of observations on the reflection of heat j and the Italian
physicist Melloni has traced the whole passage of heat-
rays through different solid bodies. All these discoveries
are clearly and simply described in Professor TyndalFs
work on 'Heat,' where you may also find the great addi-
tions that he has himself made to the work of these men.

We must content ourselves here with remembering that
the physicists of the nineteenth century have shown that
heat is 'a mode of motion,' and have traced it through
all its many wanderings both in earth, air, and sky. They
have even followed it from the sun down to our earth,
through the plant-world into the beds of coal which are
stored up in our rocks, and back again, when this coal is
burnt, to the motion which carries our steam-engines and
steam-ships across the world. All this lies before you to
study in books of scien'ce, but now we must pass on to
new discoveries in two remarkable sciences, namely, elec-
tricity and magnetism, which, we shall find, are closely
bound up with heat and motion.

Chief Works co7tsulted, — Rumford's 'Essays,' vol. ii. — 'Friction a
Source of Heat,' 1798; Davy's 'Works,' vol. ii. — 'Essay on Heat
and Light ; ' Joule's ' Mechanical Equivalent of Heat ' — ' Phil, Trans.,'
1850; Mayer's 'Forces of Inorganic Nature' — 'Phil. Mag.,' 1843;
Tyndall's ' Heat a Mode of Motion ; ' Watts's ' Diet, of Chemistry,'
art. 'Heat ;' Clerk-Maxwell's 'Theory of Heat.'

cii. XXXV. OERSTED. 341

CHAPTER XXXV.

SCIENCE OF THE NINETEENTH CENTURY (CONTINUED).

Oersted discovers the effect of Electricity upon a Magnet — Electro-
magnetism — Experiments by Ampere on Magnetic and Electric
Currents — Ampere's Early Life — Direction of the North Pole of the
Magnet depends on the course of the Electric Currents — Magnetic
Currents set up between two Electric Wires — Electro-magnets
made by means of an Electric Current — Arago magnetises a Steel
Bar with an ordinary Electrical Machine — Faraday discovers the
Rotatory Movement of Magnets and Electrified Wires — Produces
an Electric Current by meams of a Magnet — Seebeck discovers
Thermo-electricity, or the production of Electricity by Heat —
Schwabe discovers Periodicity of the Spots on the Sun — Sabine sug-
gests a connection between Sun-spots and Magnetic Currents — This
proved in 1859 by observations of Carrington and Hodgson —
Electric Telegraph — Wheatstone — Cooke — Steinheil — Morse —
Bain.

Oersted discovers the Effect of Electricity upon a Mag-
net, 1820. — We left the history of electricity at p. 264, at
the point where Volta had shown in 1800 that two diffe-
rent metals joined by a wire and placed in acid and water
will set up two currents of electricity flowing in opposite
directions from one metal to the other along the wire, and
back through the water. Every galvanic battery^ that is, an
apparatus for producing electricity by chemical action, is
made on this principle. You will hear of Grove's battery,
Bunsen's battery, Daniell's battery, and many others, all of
which have been invented in the present century ; but all

342 NINETEENTH CENTURY. rx. in.

these are only different and more perfect methods of carry-
ing out Volta's discovery. The next great step in the study
of electricity was made by Oersted, Professor of Physics at
Copenhagen, in 1820, twenty years after the invention of
the voltaic pile.

Hans Christian Oersted was born in 1777, and died in
185 1 ; he was a very eminent man, and wrote many works in
Latin upon chemistry and magnetism, but the one discovery
which has made him famous was that of electro-magnetism.
We have seen (p. 53) that the invention of- the mariner's
compass in the fifteenth century arose from Flavio Oioja
noting that a needle which has been rubbed along a piece of
loadstone always points north and south. But why should
the needle lie in this direction ? What force m^akes it turn
round when you leave it free after placing it another way ?
Ever since the fifteenth century people had asked this ques-
tion, and when Volta and Franklin showed that electrical
currents are constantly passing to and fro in our atmosphere,
scientific men began to consider whether it might not be
some force like electricity which acted upon the magnet ; es-
pecially as it had been observed that when a ship was struck
by lightning, the needle of the mariner's compass was some-
times thrown quite out of its right position.

Still nothing was really known until the year 18 19. In
that year, when Professor Oersted was one day making some
galvanic experiments at a lecture, it happened that a magnetic
needle poised upon a point (as in Fig. 54) was standing
near the wire along which an electric current was passing.
All at once, when the current was very strong, the needle
became excited and began to turn round upon the point.
Oersted and his assistants were much surprised at this, and
the consequence was that for several months Oersted made

CH. XXXV.

ELECTRO MA GNETISM.

343

a series of experiments by which he proved that an electric
current passing near a magnetic needle will always make it
turn round so as to lie across the path of the ctcrretit.

For example, if the bar of copper wire a b, supported on
the glass rods <f, e, be so placed that the end b points to the
north and a to the south, then the magnetic needle c will
lie exactly in a line with the bar, because a magnet always
points north and south. But if the two ends of the copper
rod a^ bf are fixed to the wires of a voltaic battery d, Fig. 54,
so that an electric current runs along the rod from a to b,
then the north end of the needle will begin to move away
from the north towards the west, that is towards the left side

Fig. 54.

Magnet turned by an Electric Current.

a h. Rod of copper wire. c\ Magnetic needle, d. Voltaic pile (explained p. 263).
e e, Glass supports to prevent the current running down to the ground.

of the current j and it will turn more and more as the current
grows stronger, till it lies right across it, pointing direct east
and west.

This was a very grand fact, and it has become the begin-
ning of a new science called electro-magnetism, for it shows
that electricity and magnetism act upon each other in some
peculiar way. Oersted did not publish an account of his
experiments until 1820, and then the whole of Europe rang
with the news of the discovery.

Ampere, 1775-1864.— One of the first men who heard

344 NINETEENTH CENTURY. pt. ill.

of it was Ampere, one of the professors at the Ecole Poly-
technique in Paris. We must pause a moment to learn
something of the early history of this man, for it is very inte-
resting. Andre Ampere was born at Lyons in 1775. When
he was quite a little boy he delighted in arithmetic, and
used to do long sums for his amusement by means of little
pebbles which he arranged in groups. Once when he had a
severe illness his mother took the stones away, but, having
left him alone one day for a little time, she found on her re-
turn that he had broken his biscuit into little bits and was
using them to work with instead of his lost pebbles. As he
grew older his father began to teach him Latin, but the boy
disliked it so much that it was given up, and he devoted all
his time to Algebra and Euclid.

One day he persuaded his father to take him to his friend,
the Abbe Daburon, to borrow the ^vritings of Euler and
Bernouilli, two great mathematicians. The Abbe stared at
this little boy, only twelve years old, asking for books which
very few men could understand. ' Do you know, my little
fellow,' said he, ' that these works are Avritten in Latin, and
that the differential calculus is used in them ? ' Andre's
countenance fell for a moment, for he knew neither of these
things. But he soon brightened up again. * Never mind,'
he replied, * I can learn them,^ and he set to work that very
day to learn Latin with his father, and the differential calculus
with the Abbe, and in a few months was able to come back
for the books he coveted.

Before he was eighteen he had not only read the whole
of Laplace's 'Mecanique Celeste,' but had even worked
out all the complicated problems in it. He had, however,
overtaxed his brain, and when his father was killed in the
terrible French Revolution of 1793, the grief broke down his

CH. XXXV.

AMPERE.

345

intellect. For a whole year he was almost an idiot, and it
was a long time before he could take up his mathematical
studies again. When he did, it was with his old love of
work, and he became a teacher first at Lyons, and afterwards
in Paris.

Ampere's Experiments upon Magnetic and Electric
Currents, 1820. — This was the man who heard of Oersted's
discovery in 1820. You can imagine the delight with which
he seized upon the new idea. He worked at it incessantly, as
he had done with his pebbles when a boy, and before a week
was over he had proved several new facts about electro-
magnetism. He found that it was quite true as Oersted had
said, that the magnet always lies across the electric current;
but he showed that the north pole of the magnet turns
different ways, according to the direction in which the

Fig. 55.

Fig. 56.

d ^

r

•

i

^

*

|M

V

/

Q

m

S

^

^

N

M

^p

^"^

k

'^S

f

E

1

£?-^=-£-

Diagrams showing the direction of a Magnet acted upon by Electric Currents.
a, b, c, d. Direction of current.

current flows. Thus, if the current ^ flows from sotctk to north
above the magnet, in the direction a b, Fig. 55, then the
north pole of the magnet turns towards the west ; but if it
runs from north to south above the magnet, in the direction

' You must bear in mind that there are always two cuiTents, one
from the negative and the other from the positive pole of the battery ;
but to avoid confusion the positive current is always spoken of as t?ie
current.

346 NINETEENTH CENTURY, pt. hi.

a b, Fig. 56, then the north pole turns towards the east.
Again, if it runs from north to south below the magnet, in
the direction c d, Fig. 55, the magnet will again turn to the
west ; while lastly, if it runs from south to north below the
magnet, c d, Fig. 56, the north pole turns again to the east.
In order to remember these different directions easily,
Ampere gave something like the following rule. If a man
will imagine himself to be standing so that the positive current
would come out of his mouth and return by his feet ^ the north
pole of the magnet will always be on his left-hand side. If
you are fond of standing on your head, and will try the
positions in Figs. 55 and 56, you will see that this is so— the
north pole of the magnet will always be towards your left
hand.

Magnetic Currents set up between two Electric Wires. —
The next discovery which Ampere made was a very impor-
tant one. It was already well known that two magnetic
needles will either attract or repel each other according to
the position of their poles. Thus, if the north pole of one
needle is held towards the south pole of another, they are
attracted strongly together, but if the two north poles are
brought near together, the movable needle is repelled. Now
Ampere argued that if an electric current always causes a
magnetic current across itself, then two electric wires side by
side will have magnetic currents running across them,and they
ought to attract or repel each other as if real magnets were
lying between them. And this he proved to be true. He
put two wires side by side in such a position that they could
move freely, and when he sent an electric current in the
same direction through each of them they moved towards
each other-; while, if he sent the currents one way through
one wire and the other way through the other, they drew

CH. XXXV. EXPERIMENTS IN MAGNETISM. 347

apart ; exactly in the same way as magnets attract or repel
each other, according to the direction in which they lie.

This may be difficult to understand without more expla-
nation, but you can remember that Ampere proved that eke-
tric*currents J>roduce magnetic cui'rents at right angles to them-
selves in the air, without needing any bar of steel to help them.

Electro-magnets made by means of an Electric Current.
— It now occurred to Ampere that if electric currents give
rise to magnetic currents he ought to be able to magnetise a
steel bar by passing an electric current round it. So he
wound a copper wire (covered with silk to prevent the
electricity running into the iron) round a steel bar, and,
fastening the two ends of wire to a voltaic battery, he passed
a current through it (see Fig. 57). After a short time he took

Fig. 57.

^is^^^s^iet^K^Ki^^c^^i^^

Coll of Electrified Copper Wire turning a Steel Bar into a Magnet.

the bar out and found it was a perfect bar magnet, which
would attract iron. The current of electricity, in passing
along, had magnetised the steel just as if it had been
rubbed on a loadstone.

Steel is very close and hard, and when he used a steel
bar the magnetism remained after it was taken out of the
electric wire, but if he used a piece of ordinary soft iron the
magnetism passed away when the current ceased. He called
these magnetised bars electro-magnets, because they are made
by electricity. You can easily make them for yourself, and
you will find that an iron rod will hold up needles, nails, or
even keys as long as the current is passing, but they will all
fall off as soon as it stops, showing that it is the electric
current which causes the iron to act as a magnet.

348 NINETEENTH CENTUR K pt. iil

Professor Arago, whom we mentioned before (p. 311) as
making experiments on light, succeeded in magnetising a
steel bar with currents from an ordinary electrical machine,
that is, a glass cylinder rubbed against silk, instead of using
a battery. *

Michael Faraday, 1791-1867. — We must now travel
back to England, where one of our greatest philosophers was
watching these new discoveries with intense interest. Michael
Faraday, the son of a poor journeyman blacksmith, was born
at Newington Butts in 1791. When he was thirteen years
old he went as errand boy to a bookseller named Mr.
Rieban, in Blandford Street, Manchester Square, and it was
there that the books fell into his hands which first awoke
his love of science. Mrs. Marcet's ' Conversations on
Chemistry,' Lyons's ' Experiments on Electricity,' and other
books of a like kind made the lad long for more knowledge
about these wonderful sciences. He constructed an elec-
trical machine, and spent his evenings in making experi-
ments, and he persuaded his brother Robert to pay a few
shillings for him to attend some lectures given by a 'Mr.
Tatum on Natural Philosophy.

But one of the first great pleasures of his life was when
a customer at the bookshop, a Mr. Dance, took him to four
lectures at the Royal Institution, given by Sir Humphry -
Davy. These lectures filled him with an intense longing
to learn more, and he took the bold step of writing a letter
to Davy, enclosing the notes which he had made of the
lectures, and asking for some employment connected with
science. It will always be remembered to Davy's honour
that he did not throw this letter aside, but wrote a kind
reply, telling the young man to come and see him, and
in the end made him his assistant at the Royal Institution

CH. XXXV. FAI^ADAY.

319

in Albemarle Street, \vhere Faraday afterwards became Pro-
fessor of Chemistry.

It is impossible in a short sketch to give you any idea of
the simple and noble nature of the man who from that time
for more than fifty years laboured at science in the Royal
Institution. It is not yet eight years since he died, and you
may talk with many who have known and loved him, and
if you wish to learn the story of his- life you must read it in
the book called ' Michael Faraday,' written by Dr. Gladstone.
Even of his experiments we can only mention a few, for these
subjects are becoming almost too deep for us ; but those
which we must now consider were some which have helped
to make his name famous.

Faraday discovers the Mutual Rotation of Magnets
and Electrified Wires, 1821. — It was in 1821 that Faraday
began to repeat for himself Ampere's experiments on elec-
tricity and magnetism, and he soon saw that if an electric
current going round a wire gave rise to magnetic currents at
right angles to it, he ought to be able to make an electric
wire revolve round a magnet, and a magnet round an elec-
tric wire. Accordingly, he took two cups of mercury, a b.
Fig. 58, p. 350, and drilling a hole in the bottom of each, he
passed the wires e^ e', of a battery up into them j then he
took two magnets d, d' ; d he fastened by a thin thread to
the battery wire in the cup a, so that it floated upright in
the mercury, and the top of it could move round easily ; the
other magnet, d, he fixed firmly upright in the cup b. He
then hung the copper rod c above the cups, so that the end
f, which was fixed, dipped into the cup A, and the other
end, which was made of a loose moveable wire, f, dipped
into the cup b. Thus in a the magnet was free to move
and the wire was fixed, while in b the wire was free to move

35^

NINETEENTH CENTURY,

PT. III.

and the magnet was fixed. He now sent a current through
the wires e, e', and immediately in the cup a the magnet d
began to move round the fixed wire^ while in b the wire/'
moved round the fixed magnet, d'. In this way he proved
that magnetic and electric currents move round and round in
circles at right angles to each other. He made the magnet go

Faraday's Experiments on the Rotation of a Magnet and of an Electric Wire

(Brande).

A B, Section of cups of mercury, c. Copper rod. The current coming in at e passes
up through the mercury in a, and along the rod c down into the mercury in b,
and back by ^ to the battery. On its way it causes the floating magnet, d, to
revolve round the rod, f, and the loose wire, _/', to revolve round the fixed
magnet, d!.

a great way round the circle, but not spin quite round as
the wire had done. Ampere, however, who repeated the
experiment, succeeded in making the magnet spin round and
round like the hands of a clock.

Electric Current produced by means of a Magnet.—
Faraday's mind was now full of the wonderful effect which
electricity and magnetism produce on each other, and he
began to consider whether it might not be possible to reverse
Ampere's second experiment (p. 347), and instead of making
a magnet by means of an electric current, whether he might
not set up an electric current by means of a magnet.

CH. XXXV.

THE INDUCTION COIL.

351

To try this he wound from 200 to 300 yards of wire
round a hollow cylinder a, Fig. 59, and carried the two
ends of the wire to a little instrument b, called a galvano-
meter, which was invented by Ampere, and the needle of
which moves directly the slightest current passes through it.
He then took a powerful bar magnet, c, and held it within the
cylinder. The moment he put it in, the needle of the galvano-
meter showed that an electric current had passed through

Fig. 59.

Faraday's Experiment on creating an Electric Current by means of a Magnet

(Ganot).

a. Coil of wire round a wooden cylinder connected at the two ends with b, a galvano-
meter, the needle of which shows directly a current passes through the wire ; c, a
powerful magnet.

the wire in one direction, and the moment he drew it out
another rush of electricity occurred in the other direction,
showing that the magnet had set up an electric current in a
coil of wire. While the magnet remained in the cylinder
there was no current \ it was only at the moment of going in
and coming out that it produced the effect. By a more
complicated apparatus Faraday succeeded in making these
currents strong enough to produce electric sparks ; and it is

352 NINETEENTH CENTUkY. pt. iir.

on this principle that the induciion-coil is made which is
now used to increase the power of the electricity coming
from an electric battery.

Professor Seebeck discovers Thermo-electricity, or the
Production of Electricity by Heat. — The fact was now
clearly established that electric and magnetic currents move
at right angles to each other, and this gives to a certain
extent the answer to our question. Why does a magnet
turn to the north? Ampere suggested quite early in the
discussion, that if an electric current will turn metals into
magnets, the electric currents which we know are flowing
from east to west round our globe, may turn the earth
(which is full of metals) into a great magnet. But it is
also true that exactly the opposite effect is possible, and that
the magnetic currents may be started ^by some other cause
and may set up the electric currents, so that we do not
really know which gives rise to the other.

An interesting discovery was, however, made in 1822
by Professor Seebeck, showing a possible cause of the
electric currents flowing from east to west. He wished to
try whether he could not give rise to a current of electricity
in two metals by merely using heat instead of acid and
water. For this purpose he took a half ring of copper and
fastened to it a bar of a metal called antimony, so that the
two metals had the form of a stirrup, and inside this stirrup
he hung a magnetic needle, which would show if any
current passed along the metals. Then he heated one of
the corners where the metals joined, and immediately the
magnet began to turn, showing that an electric current was
passing through the copper, and back through the antimony.
He tried this with many other metals, and in every case
when one of the parts where they joined was made hotter

CH. XXXV. SCHWABE AND SABINE. 353

than the rest, a current of electricity was caused. This he
called thermo-etedricity^ or electricity caused by heat, and it
gives us another beautiful instance of the transformation of
energy. We saw in chapter xxxiv. that heat is altered mo-
tion and motion altered heat ; since then we have learnt that
electricity produces magnetism and magnetism electricity,
and now we have heat in its turn causing electricity, while
we know from the electric spark that electricity produces
both light and heat. In all these changes we see additional
proof that force or energy cannot be destroyed, but only
exhibits itself in different ways.

But to return to the magnet. Seebeck's experiment sug-
gests a possible answer to the direction of the magnetic
needle to the north. Our globe is composed of different
metals and earths, and is always turning round from west to
east, so that one part after another comes under the heat of
the sun, and is made hotter than the rest. Therefore, since
heat produces electricity, it has been suggested that this may
cause the electric currents to flow round from east to west,
as they did through the metals in Seebeck's stirrup, thus
inducing magnetic currents to flow round from north to
south. Our knowledge on this subject is, however, very
imperfect, and the observations of which we shall next speak
seem to point to some closer connection between the sun
itself and magnetic currents.

Periodicity of the Spots on the Sun, and their Effect on
the Earth's Magnetism, discovered by Schwabe and Sabine,
1825-1859. — It was mentioned at p. 92 that Galileo and
other astronomers of the seventeenth century first observed
that from time to time dark spots appear on the face of the
sun. These spots were much studied by the astronomers
who came after Galileo; but Sir William Herschel was the

354 NINETEENTH CENTURY. pt. hi.

first to suggest in 1793 that they are caused by the opening
of bright luminous clouds which float round the sun, and
break away sometimes in one place and sometimes in an-
other, allowing us to see down through the gap into the
body of the sun itself, which thus has the appearance of a
dark spot. This is the explanation now received by astro-
nomers as most probable, and it accounts for the constant
appearance and disappearance of the spots.

In the year 1826, a well-known German astronomer,
Herr Schwabe, of Dessau (who died in 1874), determined to
take regular notes of the periods when there were most spots
to be seen on the face of the sun. Every day during twelve
years, when the sky was clear enough for him to observe the
sun, he examined it through his telescope, and noted how
many spots he could see.

In this way he discovered that there was a regular de-
crease in the number of spots for about five years and a
half, and then during the next five and a half years a gradual
increase, till they were very numerous indeed. This led him
to think that the spots went through a complete round 01
cycle of changes in about eleven years j but as he found it
difficult to persuade other astronomers of the fact, he actually
carried on his daily observations for twenty years longer, and
then, at the end of thirty-four years of daily observation, he
was able to assert boldly that he had established the truth of
his theory.

He had now kept an account of three periods of eleven
years. ■ At the beginning of each of these periods the sun
was for some time smooth and almost free from spots ; then
from year to year they increased, till, at the end of five and
a half years, as many as fifty or sixty could be seen at one
time. Then they decreased again till, at the end of another

CH. XXXV. SPOTS ON THE SUJV. 355

five and a half years, the sun's face was comparatively smooth
and spotless. During the time that Schwabe was studying
these changes, other men in the different observatories of
Europe had noticed some remarkable peculiarities about the
magnetic needle. As long ago as 1722, a famous astronomer
named Graham pointed out that the magnetic needle shifts
from side to side a little every day as the sun passes from
one side to the other of the globe. The movement is so
small that it cannot be seen without very accurate instru-
ments, but it shows that the sun's course does affect the
magnet ; and when very careful notes began to be made in
different observatories, it was noticed that this daily shifting
was greater some years than others. In 1850 an astronomer
named Lamont, of Munich, pointed out that the movement
became greater each year for about five and a half years, and
then grew less during the same period ; this led Sir Edward
Sabine to suggest that perhaps the spots on the sun had
something to do with the magnetic currents, since they both
went through a regular cycle of changes in about eleven
years.

And now comes a curious proof of the truth of this
theory. In September 1859, when a famous sun-gazer,
Mr. Carrington, was observing and measuring the spots on
the sun, he suddenly noticed a bright spot break out on the
sun's face j and fortunately another observer, Mr. Hodgson,
who was in another part of England, saw this same spot at
the same moment. The whole time from the appearance till
the disappearance did not exceed five minutes, but when
inquiry was made, it was found that the three magnetic
needles at Kew, which keep a register of their own move-
ments, had all been jerked strongly exactly at this time.
Nor was this all : the magnetic currents passing through our

356 NINETEENTH CENTURY. pt. iii.

atmosphere at that moment set up such strong electric cur-
rents in the wires of the telegraphs all over the world, that the
signalmen at Washington and Philadelphia received severe
electric shocks; a telegraphic apparatus in Norway was set
on fire, and a stream of electric light followed the pen of
Bain's electric telegraph, which writes down the message on
chemically prepared paper. Moreover, beautiful auroras
were seen in both hemispheres, and these brilliant lights are
believed to be caused by magnetic currents. The magnetic
storms on this occasion lasted for several days, and there
could no longer be any doubt that the sun at a distance of
nearly 92,000,000 miles can produce a complete hurricane
of magnetic disturbance on our earth. This connection of
the storms with the sun-spots seems indeed, as I have said,
P- 353> to suggest that the sun must have the power of pro-
ducing magnetic currents in some more direct way than
merely through the action of electric currents set up by the
varying heat on different parts of the earth.

Invention of the Electric Telegraph by Wheatstone and
Cooke, 1837. — We have spoken in the last paragraph of the
electric telegraph, and though this is more strictly an inven-
tion than a step in science, yet we can hardly close an
account of electricity and magnetism without showing how
the discovery of these two forces has made it possible for
our thoughts to be carried in a few moments of time across
land and sea to the most distant parts of the world.

Ever since Volta showed, in 1800, that an electric current
can be sent for any distance along a wire the two ends of
which are joined to the poles of a battery, scientific men had
speculated whether it might not be possible to use this
current for making signals at a distance. But there was
always the difficulty of how to make the signs at the other

CH. XXXV. WHEATSTONE AND COOKE. 357

end. In 18 16, Mr. Ronalds, of Hammersmith, hung pith-
balls on to a wire, which stood out while the current was
flowing, and fell do^vn again when it ceased; and many other
such plans were tried, but none succeeded well.

When Oersted, however, showed in 181 9 that an electric
current will cause a magnetic needle to turn from side to
side, it was clear that here was a means by which signs could
be made at any distance; and accordingly we find that
Ampere, in 1830, proposed to work signals by a magnet, and
diiferent attempts were made in Europe and America to carry
out his idea. The first electric telegraph of any value was
patented by Professor Wheatstone and Mr. Cooke in June
1837 ; and during the same year Dr. Steinheil, of Munich,
and Professor Morse, of America, both invented telegraphs
of rather different kinds. I shall not attempt to describe
all of these, but will only explain the simplest principle of an
electric telegraph as it is used in England, and to show
how it depends upon electricity and magnetism.

You will see, if you turn back to Figs. 55 and 56, p. 345,
that when the electric current flowed round one way, a b c
d, Fig. 55, the north pole of the needle turned to the west ;
when it flowed round the other way, abed, Fig. 56, the north
pole turned to the east. Now the signals of the electric tele-
graph depend upon this fact, that the direction of the current
alters the direction of the magnet. When one man wants
to send a message to another, he does it by sending an
electric current from a battery along a telegraph wire, so
that it passes a magnetic needle either from right to left or
from left to right. When it flows round one way, the needle,
even if it is a hundred miles off, turns to the right, when it
flows round the other way the needle turns to the left ; and
it is agreed that so many strokes to the right mean one

358 NINETEENTH CENTURY. pt. hi.

letter, and so many to the left another letter, and in this
way a message can be spelt out, however far off the two men
maybe. «

This is the whole secret of the electric telegraph j but to
understand how it works you must follow the explanation of
the two diagrams (Figs. 60 and 61), very carefully. Suppose
that a message is going between London and York, four
things are wanted to convey it: — i. A battery to produce an
electric current. 2. A wire to carry the current. 3. A gal-
vanometer, that is a box. A, a', holding a magnetic needle to
make the signs. 4. A little box called a commutator, b, b',
in which the position of the wires can be changed so as to
send the current first one way and then another.

1. The battery is an ordinary chemical battery such as
has already been explained.

2. The wire is stretched from station to station, resting
on little earthenware cups to prevent the electricity running
down the poles into the earth, and is arranged in a coil round
the magnetic needle at each station in such a way that when
the current flows from left to right the needle will turn to the
right, when it flows from right to left the needle will turn
to the left. You will observe that there is only one wire in
the diagram, although we know that no current will pass
unless there is a complete circuit from the battery, going
out at one pole and coming back to the other. At first
telegraphs were made with a second wire to return the
current, but Steinheil discovered that this is not needed,
for that, if the ends of the wires are sunk in the ground,
with plates of copper, f g, fastened to them, the earth
itself will act as the second wire, and carry back the re-
turn current to the battery. It is not known precisely how
the current returns ; it has been suggested that the earth is

CH. XXXV.

THE ELECTRIC TELEGRAPH.

359

a great reservoir, as it were, of electricity, so that when the
current runs into it at one place an equal amount must run
out at another ; but all that is really known is that the whole
globe acts practically as a return wire.

3. The magnetic needle is made of two or more parts, for
since it would be very inconvenient if the pointer were always
trying to turn to the north, this is avoided by fastening two
needles side by side, with the north pole of the one lying

Fig. 60.

yiiiiiiH

Fig. 61.

LDh/OON

YORK

Diagrams showing the general principle of the Electric Telegraph. •

A, a', Galvanometer, or box containing the magnetic needle. B, b'. Commutator, or
box in which the telegraph wire and earth wire are joined to each other as in a',
or to the battery, as in b. c, d, Telegraph wire, e. Earth wire, f, g. Copper
plates at the end of the earth wire. The arrows show the direction of the positive
current.

against the south pole of the other, and thus, as the earth
attracts each needle in a different way, the pull is neutralized.
This double needle is called aa'asfatic needle, and it is so
placed in the box a in the form of telegraph Vv^e are de-
scribing, that one needle is inside surrounded by the wire,
-while the other is outside on the face of the box.

36o NINETEENTH CENTURY. pt. hi.

4. The com7nutatoi% b, is a box with an apparatus inside
which is so arranged that by turning a handle (not shown
in the diagram) different ways the earth wire and telegraph
wire can be joined together, or either. of them can be joined
to one of the poles of the battery.

The commutator and galvanometer are really made in
one instrument, but I have drawn them separate to make it
more clear.

Now, when the man in London wants to send his message
to York, he first sends off a current which rings a little bell
at all the stations along the line to call attention, and then
spells out the word York. This warns the man at that
station to turn the handle of his commutator, b', so that the
telegraph-wire, d^ and the earth- wire, g, are joined together.
Then the message can be sent. The man in London turns
his handle according as he wishes the current to go. In
Fig. 60 he has turned it so that the telegraph wire, c, is
joined to the positive pole of the battery, and the current
will pass above ground along c d to the galvanometer a',
turning the needle to the right, and will then go back through
the earth hy g/e to the battery. But in Fig. 61 the man
has altered the handle, and now the earth wire, e, is joined
to the positive pole, and so the current passes underground
Sit e f, and out at^, and entering the galvanometer on the
left side, turns the needle to the left, and goes back by the
telegraph wire, d c, to the battery. In this way he turns it
from right to left as he will, and spells out the message thus :
Left, right J = A ; left, right, left, left, ^/^^ = L; left, right,
right ,// = W ; left, \ = E ; therefore J ; J, ; J, ; J/;
v; ^\^^^ v/u 3 spells ' all wellJ

It is not necessary to have a separate wire for every tele-
graphic station : one wire will do all the work so long as it is

CH. XXXV. THE AMERICAN TELEGRAPH. 361

only used by one man at a time. Therefore at every station
there is a galvanometer to point out the message, a battery
to provide the current, and a commutator to change the
current ; but these are not joined to the general wire unless
they are being used. In Morse's American telegraph, which
is generally used on the Continent, the needle pricks holes
in a strip of paper, so that the message can be kept, and
Bain's electro -chemical telegraph writes down the marks on
chemical paper. But all these are only improvements of the
same principle by which an electric current going first one
way and then another acts on a magnetic needle.

Chief Works consulted. — Lardner's * Cyclopaedia ' — ' Electricity,
Magnetism, and Meteorology;' 'Annals of Philosophy,' New Series,
1822, vols. ii. and iii. ; 'History of Magnetism ;' 'Encyclopaedia Me-
tropolitana,' art. ' Electro -Magnetism ;' Faraday's 'Experimental Re-
searches in Electricity,' 1859; Tyndall's ' Faraday as a Discoverer ; '
Gladstone's ' Michael Faraday ; ' * Nouvelle Biog. Universelle ' — * Am-
pere,' 'Oersted' ; Ampere, ' Observations Electro-dynamiques,' 1822;
Faraday, ' Various Forces of Nature ; ' Proctor, * The Sun ; ' Her-
schel's ' Familiar Lectures ; ' Brande's * Manual of Chemistry.'

IT

362 NINETEENTH CENTURY, pt. Iir.

CHAPTER XXXVI.

SCIENCE OF THE NINETEENTH CENTURY (CONTINUED).

Davy discovers that Nitrous Oxide produces Insensibility — Laughing-
gas — Safety-lamp, 1815 — Nicholson and Carlisle discover Decom-
position of Water, 1800 — Davy discovers the effect of Electricity
upon Chemical Affinity— Faraday's Discoveries in Electrolysis —
Indestructibility of Force — Various modes discovered of Decompos-
ing Substances — John Dalton, Chemist — Law of Definite Propor-
tions— Law of Multiple Proportions — Dalton's Atomic Theory —
The study of Organic Chemistry — Liebig the great Teacher in
Organic Chemistry.

Sir Humphry Davy, 1778-1829. — We saw in the last
chapter how Oersted, Davy, Ampere, Faraday, and Seebeck,
by their various discoveries, showed the connection between
Electricity, Magnetism, and Heat. We must now learn how
the connection between electricity and chemical change was
also worked out. This was done by Sir Humphry Davy and
Faraday, who thus put England once more at the head of
chemical discovery, in which the French school of Lavoisier
had so long taken the lead. •

Sir Humphry Davy, whom we have mentioned before as
making experiments upon heat, was born in 1778, at Pen-
zance, in Cornwall, and died at Geneva in 1829. His mother
being a widow, he was apprenticed when quite young to
an apothecary, and there with wine glasses, old medicine
bottles, tobacco pipes, and a syringe, he made his first
chemical experiments. When he was scarcely twenty years

CH. xxxvL SIR HUMPHREY DAVY. 363

of age, Dr. Beddoes, a physician, who had opened a hospital
for curing patients by the use of different gases, heard so
much of the young man's abilities that he invited him to
come to Bristol; where he employed him in making experi-
ments.

In this way Davy's attention was drawn to nitrous oxide,
a gas which had been declared by a celebrated physician,
Dr. Mitchell, to be very poisonous. Our young chemist
wanted to try this for himself, and actually began breathing
it in small quantities to see^whether it would affect him. He
proved that it certainly was not so poisonous as Mitchell had
thought, and, growing gradually bolder and bolder in the use
of it, he succeeded at last in breathing the gas for several
minutes, at the end of which time he lost all consciousness,
and found himself in a land of delicious dreams, out of which
he awoke gradually without being injured in any way. En-
chanted at having discovered such a delightful sensation, he
carried on his experiments for more than ten months, and
when he published the results, and told the world that the
mere breathing of a gas could make a man sleep, and dream,
and laugh without any cause, it created a great sensation,
and Davy's name soon became well known.

At this time (iSoi) the Royal Institution had just been
founded, and Count Rumford, seeing that Davy was a young
man of great talent, offered him the appointment of Assistant-
chemist. Davy accepted it, and from that time devoted himself
entirely to science. He was young, bright, and enthusiastic,
and his lectures were so clear and eloquent, that the Royal
Institution soon became famous under his influence, while
every new appliance for making chemical experiments was
given him in his laboratory. It was here that he made his
observations on flame in 181 5, and constructed his Safety-

364 NINETEENTH CENTURY. vr. 111.

lamp, which has saved so many lives, and for the invention
of which he received the title of baronet. It was here also
that he made his first experiments in electro-chemistry, which
is the only one of his many discoveries of which we can speak.

Discovery of Electrolysis, or the Decomposition of
Water by an Electric Current, 1800-1806. — In the year
1800, two men named Nicholson and Carlisle discovered by
chance that when the two wires of a voltaic battery were
dipped in water, bubbles of gas rose np from them. They
also found by experiment that the gas from one wire was
oxygen, and from the other hydrogen; but where these gases
came from, whether they were produced by the electricity, or
came from the battery, or from the water, they could not
tell. Moreover, besides the oxygen and hydrogen which
came off, there also appeared an acid of some kind at the
positive pole, as was shown by damp litmus paper turning
red (see p. 229), and an alkali appeared at the negative pole
which turned this red litmus paper blue again. This looked
as if the electric current had produced something in the
water, for Cavendish, as you will remember,' had shown
that pure water is made of oxygen and hydrogen only (see
p. 231). Many chemists, therefore, set themselves to try
to discover what effect the electric current had on the
water, and Davy in 1806 succeeded in solving the question.

The history of his experiments is especially interesting
because it shows, as we have noticed so often before, that a
patient and careful inquiry into nature always gains a true
answer in the end. Davy did not believe that the electric
current produced anything in the water ; he thought that
both the acid and the alkali came from the vessels that were
used. So he set to work steadily to clear away all possibility
of impurities. He took distilled water, and used cups first

CH. XXXVI. ELECTROLYSIS, 365

made of agate, and afterwards of pure gold, because he
found that the clay of the china cups was acted upon by the
current. Yet, in spite of these and many other precautions,
the acid and the alkali still continued to appear. Then he
used water which he had evaporated very slowly, instead of
distilling it, because he found that distilled water carried
away some salt with it. When he had done this the acid was
weaker, but the alkali was as strong as ever. At this point
it occurred to him that the alkali might perhaps come out
of the air, so he put his gold cups of water under an air-
pump, and completely exhausted the air, filling the pump
with hydrogen to make quite sure that no other gas could be
left in. When he had tried this several times and made it
perfect in every way, he succeeded at last in getting nearly
pure oxygen at one pole and hydi'ogen at the other.

By this experiment Davy not only confirmed Cavendish's
discovery that pure water is made of hydrogen and oxygen,
but he also established a totally new method of analysing
substances, and finding out the materials of which they are
composed. This method was in some ways more certain than
Bergmann's method of tests, for when you drive one ele-
ment out by putting another in its place, you have some
difficulty in finding out exactly what has happened ; but
when a substance is decomposed by electricity you literally
take it to pieces, and see the elements of which it consists.

Discovery of Potassmm and Sodium. — Having suc-
ceeded in the case of water, Davy now went on to try
the efi"ect of the electric current on other bodies, and
the first which he took were common potash and soda,
which had always been supposed to be simple substances,
which could not be decomposed. For several reasons, how-
ever, Davy believed that it would be possible to reduce them

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into more than one substance. So he heated some pure
potash in a spoon until it was quite liquid, and fastening
the two ends of the spoon to the wires of a battery, he sent
an electric current through it. After a little while the potash
began to be agitated, and to rise up in bubbles, and then
there came to the surface beautiful silver-like globules, some
of which burst into flame, while others remained covered
by a sort of white film.

' Davy's delight,' writes his brother, ' when he saw the
minute shining globules like mercury burst through the
crust of potash and take fire as they reached the air,
was so great that he could not contain his joy— he actually
bounded about the room in ecstatic delight.' It must indeed
have been a beautiful sight in itself ; but probably Davy's
excitement arose chiefly from the new truth he saw in it.
He had proved that potash was not a simple substance,
but contained something which had never before been
discovered.

At first he had great difiiculty in collecting the globules,
for they not only burst into flame when they met the air, but
even in water they took fire, joining themselves to the oxygen
and setting the hydrogen free. At last, however, he succeeded
in collecting them in rock oil, or naphtha, which contains no
oxygen. He was then able to examine them, and he found
they were composed of a metal hitherto quite unknown, to
which he gave the name of potassiwn. A few days later he
procured the metal sodium out of common soda by the same
process.

This method of decomposing substances is called electro-
lysis^ which means ' setting free by electricity.' Davy made
use of it to decompose many earths, such as lime, mag-
nesia, &c., and the great Swedish chemist, Berzelius (bom

CH. XXXVI. FARADA TS EXPERIMENTS. 367

1778, died 1848), discovered several new chemical sub-
stances by means of it.

Faraday's Experiments on the Connection between
Electricity and Chemical Affinity. — This was the practical
use of the discovery; but it had another gi-eat interest for
chemists, because it proved that electricity can overcome
that power called ' chemical affinity/ which holds two or
more elements together in one compound substance. You
will remember that Bergmann, and indeed Newton before
him, pointed out that there is some force which causes
certain bodies to choose each other out when they meet, and
to unite firmly so as to become a new substance which
has its own peculiar characters. Chlorine and sodium, for
example, when heated, unite to form common salt, Avhich is
not the least like either chlorine or sodium when they are
separate ; and in the same way hydrogen and oxygen unite
to form water. In these new states they are held together
by a power which for want of a better name we call
' chemical attraction,* or ' chemical affinity ' (see p. 229).

Now Davy showed that an electric current conquers
this power and sets the different elements free, so that they
can each go their own way. Thus the electric current
passing through the water overcomes the force which holds
the oxygen and hydrogen together, so that, at the point
where the battery wires touch the water, hydrogen bubbles
come off on one side and oxygen on the other.

It is to Faraday, however, that we owe most of our
knowledge about the intimate connection between electricity
and chemical change. He followed up Davy's experiments,
and traced out very clearly the cause and effect of the
chemical current. He showed in the first place that a sub-
stance cannot be decomposed by electricity unless it is a

368 NINETEENTH CENTURY. pt. hi.

good conductor, so that the current passes readily along it.
Thus, ice being a bad conductor, the slightest film of ice
interposed between the water and the electric wires will pre-
vent the current from setting free the oxygen and hydrogen j
and ether and alcohol cannot be decomposed at all by elec-
tricity, because they will not conduct the current.

He also showed that the electric current itself does not
depend upon any effect which the two metals have directly
upon each other, as Volta thought, but is caused by the
chemical action going on between the zinc and the water.
Thus, if you put some zinc in sulphuric acid and water, the
zinc pulls the water to pieces, and hydrogen gas comes bub-
bling off, but if you coat the zinc with mercury, hydrogen
will no longer come off, and no action will take place till
you put another metal in the water, as for example a piece
of copper and connect the two metals by a wire. Then the
hydrogen bubbles off again, but this time it does not come
off the zinc, hut off the copper. The force which overcomes
the chemical attraction in the water has been made to travel
across the vessel from one metal to the other, and this
journey may be made as long a one as you choose, and
may even be continued for hundreds of miles if only the
current has some means of finding its way home to the first
metal at last.

Now all this is a modified result of the chemical action
of the zinc and acid water upon each other; as Faraday
proved in a most beautiful way by showing that the power
of the electric current to decompose water in another vessel
depends entirely upon the violence of the action going on
between these two elements of the battery. If the battery
is weak, the water in which the ends of the wires are dipped
is decomposed slowly ; if the battery is strong, the bubbb s

CH. XXXVI. THE STUDY OF CHEMISTRY. 369

of oxygen and hydrogen come off rapidly and vehemently.
This led him to invent a useful little instrument called a
voltameter^ which measures the quantity of water decom-
posed, and so tells exactly what is the strength of the
electric current. 'Thus we see/ says Faraday in one
of his lectures, ' that the power which decomposes water,
or produces the heat and light of the electric spark, is
neither more nor less than the chemical force of the zinc —
its very force carried along the wires and conveyed to
another place.'

And here again we find ourselves brought face to face
with the truth that all the various physical forces are only
different forms of one and the same force. We learnt before
that motion can be turned into heat and heat into motion,
while heat, magnetism, . and electricity all in the same way
give rise to each other ; and now we learn that chemical
change gives rise to electricity, and electricity in its turn to
chemical change. So that the whole set of physical forces,
heat, motion, electricity, magnetism, and chemical change,
are all different phases of one indestructible force which we
lose sight of in one shape, only to find it in another.

Methods of Studying Chemistry. — ^We have now learnt
how most of the chief methods of producing chemical
change have been worked out. The science of chemistry
consists in using these methods to test and decompose all
the substances in our earth and atmosphere, and so learning
their nature.

We have seen that there are four ways of thus analysing
compound bodies. First, by testing them with other sub-
stances which attract some of their elements, and draw them
out of the compound, as when by plunging a piece of iron
into nitrate of copper the iron attracts the nitric acid and

570 NINETEENTH CENTURY. ft. hi.

draws it out, leaving the copper to fall down as a metal.
This was the method chiefly worked out by Bergmann in
1761, and which has since then been brought to much
greater perfection by other chemists.

Secondly, by heating substances gently and examining
the vapours which rise from them, and afterwards analysing
what remains by burning. This method was fairly under-
stood by Geber, and was first applied to organic substances
by Boerhaave.

Thirdly, by passing an electric current through a com-
pound substance in a fluid state, and. so overcoming the
force which holds the different elements together and
setting them free. This method, called electrolysis^ was dis-
covered by Davy in 1806, and afterwards thoroughly worked
out by Faraday.

Fourthly, there is the method of spectrum analysis
suggested by Herschel in 1822, which was carried on with
great success by Bunsen and Kirchhoff". In this method
the substance is turned into gas either by ordinary heat oir
by the electric spark, and is then examined by the spectro-
scope j the elements being determined by the position of
the bright lines they throw on the spectrum.

There is still a fifth method, about which we have
said nothing as yet, and which was chiefly brought into use
by the chemist Berzelius (mentioned p. 366), namely the
fusing of substances by means of the blowpipe. This
instrument is merely a little tube with a mouthpiece at one
end and a very minute hole at the other. By placing the
minute hole in the middle of a flame and blowing through
the mouthpiece, the centre of the flame is made to burn
furiously, and many substances can be melted and decom-
posed by it which do not yield to ordinary heat.

CH. XXXVI. JOHN DALTON. 371

By these different methods a very large number of sub-
stances have been analysed since the time of Davy and
Faraday, and sixty-four elements or simple substances have
been discovered. It is possible that some of these may
even at some future time be decomposed and shown to be
made up of two elements ; we can only affirm that now they
appear to us to be simple substances. Some of these
elements have been brought together and made to unite
into compound substances by artificial means ; as when,
for instance, oxygen and hydrogen mixed and lighted by
a spark rush together and form water, or when hydrogen
and chlorine mixed together and placed in the sunlight
unite to form hydrochloric acid.^ This method of bringing
elements together to form a compound substance is called
synthesis^ and is exactly the opposite of analysts, or the
splitting up of a compound substance into its elementary
parts.

To follow out the gradual development of synthesis and
analysis, and to see how all the different elements and com-
pounds were in this way determined, would be to write a
work upon chemistry. There is only one other general
principle which we ought to try and understand here ;
namely, the proportions in which the elements combine to
form substances. This principle, which lies at the root of
all our modern chemistry, was first worked out by a poor
schoolmaster named Dalton.

Dalton shows that the Different Chemical Elements
always Combine in Definite Proportions. — John Dalton
was bom of Quaker parents in 1766, near Cockermouth, in

' Sir H. Davy was the first to discover, in 1807, that hydrochloric
acid is made merely of hydrogen and chlorine ; before then it was
believed that every acid must have oxygen in it.

372 NINETEENTH CENTURY. rx. in.

Cumberland. He received the ordinary education of a village
school, and after being master of a small academy at Kendal,
he went to Manchester, where he supportect himself all the
rest of his life by teaching mathematics.

Fortunately for science, a blind gentleman named Gough
became interested in him, and gave him the use of his
library and chemical laboratory, which enabled Dalton to
work out many useful facts, and to establish the laws which
are now the guide of all chemists, though they differ about
some of his conclusions.

You will remember that it was only in the time of
Lavoisier that chemists began to weigh carefully the gases
into which substances can be decomposed. Before then it
had been thought sufficient to say that a substance contained
sulphur, mercury, carbon, &c., without saying how much of
it there was. But after the discovery of oxygen, when the
real nature of chemical change began to be understood,
chemists saw the importance of weighing accurately the
different elements into which a substance can be broken up ;
and when this had been done for some time, and a great
number of analyses had been made, it was seen that any
given chemical compound always contains the same elements
combined in the same proportion.

Thus, for example, all water, whether it comes from rain,
snow, dew, steam, or exploded oxygen and hydrogen, will
always be found to contain two parts by weight of hydrogen
to sixteen parts by weight of oxygen ; so that if you decom-
pose 1 8 ounces of water you will collect «

2 volumes of hydrogen weighing i oz. each . . 2 ozs.
I volume of oxygen weighing i6 ozs. . . . i6 ozs.

1 8 ozs.

CH. xxxvi. LAW OF DEFINITE PROPORTIONS. 373

And this never varies. Again, if you take some ammonia
and decompose 1 7 ounces of it you will collect

3 volumes of hydrogen weighing I oz. each . . 3 ozs.
I volume of nitrogen weighing 14 oz. . . .14 ozs.

17 ozs.

And this again never varies. Wherever you get ammonia it
will always be made up of these proportionate weights of
hydrogen and nitrogen.

This combination of the different elements in fixed
quantities is called the law of definite proportions. It was
hinted at by four chemists before Dalton j namely Proust,
Wenzel, Higgins, and Richter, but it was very little under-
stood, and some eminent chemists, such as Berthelot, even
doubted whether it was true. Dalton, however, made a re-
markable discovery which both proved the truth of the law
itself and showed that it meant a great deal more than had
been imagined.

He found that not only are the elements in any one
substance always in a fixed proportion, but that each ele-
ment, such as oxygen, has a weight of its own, and will
only combine with other elements in proportions of this
fixed weight. For example, oxygen will join itself to
nitrogen in five different proportions, making five different
substances, and in each case the same fixed weight of oxy-
gen is added. Thus, if you decompose 22*4 litres of

Volumes of Weighing

Nitrogen Oxygen Nitrogen Oxygen

Nitrous oxide, you will get 2
Nitric oxide ,, 2

Nitrous acid ,, 2

Nitric peroxide , , 2

Nitric acid ,, 2

So that each substance contains one more volume of oxygen

. . I

. 28

grammes

16 grammes

. . 2

. 28

5>

32

• • 3

. 28

>J

48 „

. . 4

. 28

>>

64 „

. • 5

. 28

> J

80 „

374 NINETEENTH CENTURY. pt. hi,

compared to the nitrogen than the one before it j and this
volume always weighs i6 grammes^ while each volume of
nitrogen weighs 14 grammes.

Oxygen behaves in this way in all compounds, only
joining itself to other elements in weights of 16 or multiples
of 16. Thus, if you heat mercury as Lavoisier did, so that
it takes up oxygen out of the air, 200 parts by weight of
mercury will combine with 16 of oxygen and no more. If
you heat carbon with oxygen, 1 2 parts by weight of carbon
will take up 16 of oxygen to make carbonic oxide, or twice
16=32 to make carbonic acid, but it will not take up any-
thing between these weights. This same law holds true of
all the elements, each one having its own peculiar weight.
Nitrogen, for example, combines in weights of 14, or twice
14=28, or three times 14=42, &c. \ sodium in weights of
23, 46, and 69, &c. This is called the law of mtdtiple pro-
portmis, which we owe entirely to Dalton, and it is a fact
about which all chemists agree. Dalton went on to try and
explain it by a theory which is still a matter of speculation,
and which some chemists do hot receive.

Dalton's Atomic Theory, 1808. — In order to explain why
each element should have its fixed weight in which it always
combines, Dalton imagined, as Democritus, Epicurus, Bacon,
and Newton had done before him, that all matter is com-
posed of tiny parts, or atoms, which are too small to be seen
and which cannot be divided. These atoms, which he
pictured to himself as round grains like very small shot,
would be of the same size in every substance, but not of the
same weight. Hydrogen atoms would be the lightest of
all, for hydrogen is the lightest substance known ; oxygen
atoms would be 16 times, and nitrogen 14 times, as heavy
as those of hydrogen.

CH. XXXVI. THE ATOMIC THEORY. 375

Now when two elements combine together they cannot
take up less, according to Dalton, than one atom of each, or
two atoms of one to one of the other, and so on, and there-
fore exactly the weight of an atom of any substance will
always be added. For example, to turn back to our table
on p. 373, Dalton wOuld say that a molecule^ or the smallest
portion which can be imagined, of nitrous oxide will contain
2 atoms of nitrogen weighing 14 each to i atom of oxygen
weighing 16 ; while nitric acid will contain 2 atoms of nitro-
gen = 28, and 5 atoms of oxygen, 5 x 16=80. If half an
atom of oxygen could be added, then it might be possible
to take up 16 + 8, or 24 parts of oxygen; but as the atoms
are supposed to be indivisible, this cannot be done, but a
whole atom weighing 16 must be added each time. There-
fore you wdll see that by an atom Dalton meant the smallest
quantity of any ele7nent ivhich can combine with other sub-
stances.

Thus, water is made up of molecules, each containing
two atoms of hydrogen and one of oxygen. But as these
atoms cannot be seen, how can it be known how many there
are in any substance, and when we have arrived at the
smallest weight of any element ? Dalton knew it in some-
thing like the following way : —

If you decompose water by electricity, you know that you
will collect two bottles of hydrogen for one of oxygen. But
you can also decompose it another way : if you take a
small piece of the metal sodium and float it on water, it will
roll round and round fizzing violently. This is because
sodium joins very readily to oxygen, and the sodium is
turning out some of the hydrogen from the water and taking
its place. When the piece of sodium has disappeared, if
you evaporate off the rest of the water, you will have a white

37<5 NINETEENTH CENTURY. pt. hi.

powder, which is caustic soda \ and if you dec.ompose this
soda, you will get out of it one measure of hydrogen, one of
oxygen, and one of sodium. The sodium, you observe, has
turned exactly half the hydrogen out of the water and taken
its place \ and this shows there must have been two atoms
of hydrogen in the water, because a single atom could not
have been divided.

In the soda we have now got the smallest quantity of
each element — sodium, oxygen, and hydrogen — which will
combine with any other. You can turn either of these
three out of the soda, but you cannot turn out a part of any
one of them. Therefore, a molecule of soda is said to be
made of one atom of hydrogen weighing i, one atom of oxy-
gen weighing 1 6, one atom of sodium weighing 23, and these
numbers are called the atomic weights of hydrogen, oxygen,
and sodium.

This will give you a rough idea of Dalton's theory of
atoms. There is always this difficulty in it that we cannot
be quite sure when we have arrived at the smallest quantity
of any substance ; for suppose that one day we were to find
that oxygen could be split up into two substances, then it
would no longer be true that an atom of oxygen could not
be divided. It would then be made up of two elements, the
smallest quantities of which, when joined together, would
weigh 16. But if we bear this possibility in mind, then the
theory is of great use in giving us the symbols which are now
used in chemical language. For when it was once agreed
that the weight of an atom of hydrogen should be reckoned
as I, then an atom of oxygen will weigh 16, and the letters
HHO express a great deal. They tell us that two atoms of
hydrogen weighing 2 are joined to one atom of oxygen weigli-
ing 16, to form a molecule of water. In the same way

CH. xxxvi. LIEBIG— ORGANIC CHEMISTRY. 377

HOjNa^ tells us that one atom of each of these substances,
weighing respectively, i, 16, 23, form a molecule of soda.
And thus a complete chemical language has sprung up, by
which chemists in all parts of the world can understand at
once what is the composition of any substance; and by
means of these simple letters the most complicated chemical
problems can be worked out clearly and intelligibly.

Dalton's theory was received very quickly by chemists,
considering how entirely new the ideas were which it
taught. His friend Dr. Thomson, an eminent chemist
(born 1773, died 1852), gave a very clear account of it in
his ' System of Chemistry,' and brought it under the notice
of Davy and Faraday ; and a great French chemist, Gay-
Lussac (born 1778, died 1850), adopted it at once, and
added another discovery in favour of it in 1809 — namely,
that when substances are reduced to gas, and the gas is
collected, it is found that the different elements combine in
equal or multiple volumes.

You will understand this by turning back to the com-
pounds of nitrogen and oxygen (p. 373), where you will see
that there was always either i, 2, 3, 4, or 5 volumes of
oxygen collected for one of nitrogen, and never a part
of a volume. This was really a different fact from the one
Dalton pointed out, that the elements combine in definite
weights, and it was necessary to complete the law of mul-
tiple proportions.

Liebig the Great Teacher in Organic Chemistry. — And
now, before closing the history of chemistry, we must mention,
in passing, one great division of the science of which we
cannot attempt to give any real account — namely, the science

» Na stands for Natrium, the Latin name for soda, now used for
the metal sodium.

378 NINETEENTH CENTURY. pt. hi.

of organic chemistry^ or the chemistry of living bodies. This
study began, as you will remember, when Boerhaave first
examined the juices of plants and the fluids in animal
bodies. But it can scarcely be said to have made any great
advance till the year 1828, when a German chemist named
Wohler first showed that urea, a substance in the bodies
of animals, can be made artificially. Since then Berthelot
and other eminent chemists have discovered how to make
many compounds in the laboratory which were before only
found in living beings.

But the great master of organic chemistry whose name
you must remember, though we can speak but little about
him, was Baron Liebig, of Darmstadt, who was born in
1803, and died only a few years ago. He was the first to
analyse organic substances satisfactorily, by heating them in
vessels with metallic oxides, and so reducing them to carbon
and their other elements ; and he also brought agricultural
chemistry to great perfection. This subject, which was first
treated by Sir H. Davy, teaches how the grov/th of plants
depends upon the chemical state of the soil in which
tliey are sown, how different crops should be sown in suc-
cession in any field so as not to exhaust the soil ; and what
manure will best give back to the ground the elements which
the plants have taken out of it. Liebig also traced out the
changes which food undergoes in our bodies, and studied
which kinds turn to fat, muscle, blood, or sugar in our system.
In 1832 he also discovered chloroform and chlorale, though
these were not used for producing unconsciousness till more
than fifteen years later by Dr. Simpson.

The whole history of organic chemistry, however, is far
beyond us It present j the science has only existed for the
last fifty years, and the chemical substances which are

4

CH. XXXVI. ORGANIC CHEMISTRY. 379

created in a living body are extremely complicated, making
the whole subject very difficult to understand. Moreover,
we do not pretend to follow out the particulars of any
science ; if you can remember the names of some of the
great pioneers of chemistry from the time of Geber in the
ninth century up to the days of Davy, Faraday, and Liebig,
and have some slight understanding of the nature of the
work they did, it is all we can attempt in a book of this
kind.

Chief Wo7'ks consulted. — Davy's 'Works,' 1840; Whewell's 'Induc-
tive Sciences;' Dalton's 'Chemical Philosophy,' 1808; Dr. Henry's
'Memoir ofDalton,' 1854; Fownes's 'Chemistry;' Brande's 'Che-
mistry ; ' Faraday's * Various Forces of Nature ; ' ' Edinburgh Re-
view,'vol. xciv. ' Modem Chemistry ; ' Hoffmann, 'On Liebig and
Faraday.'

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CHAPTER XXXVII.

SCIENCE OF THE NINETEENTH CENTURY (CONTINUED).

The Organic Sciences are too difficult to follow out in detail — ^Jussieu's
Natural System of Plants — Goethe proves the Metamorphosis of
Plants — Humboldt studies the Lines of average Temperature on the
Globe — Extends our knowledge of Physical Geography — Writes the
' Cosmos '—Death of Humboldt in 1858.

The short sketch of advances in modern chemistry given in
the last chapter brings us to the end of the physical sciences,
or those which deal more particularly with the properties of
bodies, and the laws of their action upon each other. We
must now pass on to those sciences which treat of the past
and present history of the globe and the living beings which
inhabit it. I shall not attempt to speak of these sciences
separately, for it is clearly impossible without a great deal
of special knowledge to follow the modern discoveries in
physiology, anatomy, medicine, zoology, botany, and geology.
All these sciences had advanced rapidly since the time
of Haller and Hunter, Linnaeus and Buffon. Famous
anatomists and physiologists such as the two Monros, father
and son, in England, Bichat (17 71-1802) in France,
Camper (1722-1789) and Blumenbach (1752-1840) in Ger-
many, had been carrying on the study of the comparative
structure of men and animals, and training up students to
understand, far more completely than before, the functions

cii. XXXVII. GOETHE A BOTANIST. 381

of living beings. And the followers of Linnaeus all over
the world had been collecting and sending home for com-
parison rare plants and animals formerly unknown, which
were eagerly studied for the new light they threw upon those
which had been already dissected and described.

And so it came to pass that towards the end of the
eighteenth century men became eager not merely to examine
separate specimens or structures, but to form theories about
the living beings on the globe. They began to inquire why
animals should all be so much alike in their general plan,
and yet so different in their special characters \ why the
same part of the body should be made to serve for different
purposes in different animals, instead of a special organ being
provided ; as, for example, the wing of the bat, which answers
exactly to the front leg of a mouse, but is altered so as to
be used for flying instead of walking. Then again, as the
distribution of animals became better known, the question
arose why certain kinds, such as kangaroos, should be found
only in Australia, while they are wanting in all other parts
of the world. Such general questions as these began to
occupy the minds of naturalists, and we cannot close a
history of science without trying to understand something
of the attempts made to answer them, although they are
so difficult that it will require all your attention and
thought to understand them.

The Poet Goethe proves the Metamorphosis or Transfor-
mation of Plants, 1790. — One of the first men who threw
any light upon the history of the growth of plants was the
poet Goethe. Goethe had a deep love of Nature, as may
be seen in many of his beautiful minor poems, and this love
led him in the year 1780 to devote himself to the study of
rhe anatomy of plants and animals.

382 NINETEENTH CENTURY. PT. in.

Since the time of Linnaeus botany had become very-
popular, and the two celebrated French botanists, Antoine
de Jussieu and his son Bernard de Jussieu, had established
the Natural System of plants, which obliges men to observe
every part of a plant before placing it in a class or order.
You will remember that Linnaeus suggested this method (see
p. 2ii), but thought it too difficult for ordinary students, and
even to this day the Artificial System of Linnaeus is used
side by side with Jussieu's.

The study of the Natural System, however, led botan-
ists to observe more carefully the nature of plants and the
manner in which they grow ; and when Goethe turned his
attention to botany he was very much struck with the
power which plants have of transforming or changing
the growth of their parts. For example, the common wild
rose in the hedges has a crown of pink petals, with stamens
and pistils in the centre; but the garden rose, which is
nothing more than the wild rose grown in a better soil, has
lost the stamens and pistils, or rather has changed them into
flower-leaves, so that the whole flower is one mass of petals,
and rarely forms any seeds.

It is clear, therefore^ said Goethe, that the stamens and
pistil of a plant are nothing more nor less than flower-leaves
transformed into a peculiar shape, so that they serve to form
seeds, and to carry on the life of the plant. And this is
true of all the different parts of the plants. Wherever you
look in the vegetable kingdom, you will find that every part
of a plant is nothing more than stem or leaves altered in
various ways to suit the work they have fo do. Thus the
stem of a geranium, the trunk of a tree, the twining stalk
of the vine, the straw of wheat, the thorns of a rose-bush,

CH. x-xxvii. THE METAMORPHOSIS OF PLANTS. 383

the runners of a strawberry, the roots of plants, and the
fleshy potato, are all only different forms of stems and
branches. Again, the two cotyledons of a seed which are
well seen in the halves of a bean are but the first pair of
leaves. Out of them grows the stem, and out of this, leaves
of different forms according to the peculiar species of
plant.

Then, as the plant developes, come the buds of the flower,
but these again are only stems and leaves growing more
thickly together. We find in different plants every variety
of flower from mere green leaf-like blossoms to the most
gorgeous colours. The green leaves called sepals, which
lie under the yellow petals in the buttercup, are transformed
into brilliantly coloured petals in the tulip, while in some
cases, such as occasionally in white clover, the whole flower,
sepals, petals, pistil and stamens, has been known to be
changed into little leaflets growing as if upon a branch.

For this reason gardeners find it possible to cultivate a
plant so that it shall be all leaves and no flower, or, oi\ the
other hand, shall have a gorgeous flower while the leaves
remain small and insignificant ; or, as in the potato or the
turnip, they can increase the size of the root at the expense
of the leaves and flowers. And thus we are led to see that
all the different parts of a plant are only peculiar transfor-
mations of simple stems and leaves, such as we fin^ in
mosses and the lowest forms of plants.

This beautiful truth of the transformation or metamor-
phosis of plants we owe to the poet Goethe ; for though
Linnaeus suggested it rather vaguely in some of his writings,
and a botanist named Wolff seems also to have taught it,
yet it was Goethe's essay on the ' Metamorphosis of Plants,'

384 NINETEENTH CENTURY, pt. hi.

published in 1790, which first led naturalists to consider the
question. Goethe's work was very little read at first, and
he had great difficulty in finding a publisher for it, for it was
thought that a poet could not know much of science ;
but the great Swiss botanist, Auguste de Candolle (born
1778, died 1841) seeing what a new hght it threw upon the
study of plants, taught it in his works, and then it became
gradually known as one of the greatest discoveries in modern
botany.

Alexander von Humboldt studies the Lines of Equal
Heat over the Globe— Founds the Study of Physical Geo-
graphy—Writes the < Cosmos,' 1793-1859.— While Goethe
was studying plants at Weimar, and learning the secrets of
Nature in the quiet of his own home, another man of whom
we must now speak, was planning to travel in distant
countries, and to write a history, as far as he was able, of
the work which Nature is doing all over the world.

Alexander von Humboldt, who forms a link between the
science of the eighteenth and the nineteenth centuries, was
born at Berlin in 1769, and was educated (together with
his brother William, the great politician) at the University
of Gottingen. At the age of one-and-twenty he went to
Freyberg, where he was a pupil of Werner. It was at this
time, when he was only just of age, that he formed the plan
in his mind of spending his life in studying the works of
Nature, and writing a ' grand and general view of the Uni-
verse.'

The first sketch of his book, which he called ' Cosmos,'
or 'The Universe,' was written in 1793, when he was only
twenty-four; and the last sheets were printed in 1859, when
he was ninety years of age. In the sixty-six years between
these two dates he collected and published in popular

cii. XXXVII. HUMBOLDTS TRA VELS, 385

language an immense number of facts about nature in all
parts of the world.

His chief voyage was to America in 1799, when he spent
six years in Mexico, and along the shores of the Orinoco.
Here he began one of his greatest undertakings, namely
finding out the climate of different parts of the world, and
tracing out isothermal lines, or lines of equal heat over the
globe, showing what countries have the same average
temperature, and explaining why some enjoy an almost
equable climate all the year round, while others are very hot
in summer and cold in winter. For example, he pointed
out that Greenland is much colder than Lapland, even in
places which are on the same line of latitude, because a
cold current from the North Pole flows past Greenland,
while the warm Gulf Stream crosses over from the Gulf of
Mexico and washes the shores of Lapland. The import-
ance of this study of variations of temperature was first
pointed out by Humboldt, and it should be remembered
as one of his most original investigations.

Again, in his long journeys through South America, he
traced everywhere the different species of plants which
grew at various heights, even up to 20,000 feet on the slopes
of the Andes. This led him to try and find the reasons
why certain plants are only to be found in certain areas, in
the same way that Buffon had worked out the distribution ot
animals. When he returned to Paris in 1804 he had col-
lected an immense number of facts as to the heights of
mountains, the climate of countries, the minerals and metals
found in them, the active and extinct volcanoes, the nature
of the rocks and soils, the vegetation and the animals ; and
with the help of the best scientific men in Paris (each

18

386 NINETEENTH CENTURY, rx. in.

undertaking his own special science) he published twenty-
eight large volumes, which contained the conclusions based
upon the facts he had learnt in his travels.

In 1827 he returned to Berlin, and was then invited by
the Emperor of Russia to go on a journey into the Russian
provinces of Asia, where he spent nine months making the
same kind of observations that he had made in America.
In 1830 he was sent to Paris as Prussian ambassador, and
it was not till he returned to Berlin some years after, that
he began to publish the ' Cosmos ' he had been preparing
for so long.

In this grand work he gives a complete history of
astronomy, and all the discoveries in it made up till his
time ; and then taking our own world as part of the uni-
verse, he describes the changes which are going on now, or
have been going on in past time, on the face of the earth.
It is to Humboldt that we owe much which makes geo-
graphy interesting. The study of the surface of the globe,
of mountain-chains, table-lands, and rivers, the climates of
countries, the different winds which blow, and the currents
which cross the ocean ; the way in which plants and ani-
mals are distributed over the world \ the different races of
men, and how they have spread over the globe — all these
and other facts which make geography something more than
a mere list of names, Humboldt studied during his various
journeys, and related them with a freshness which °had a
peculiar charm.

It was not so much that he advanced any one branch
of science as that he led men to look upon the earth and the
universe as one vast whole, and to find a living interest in
every part of it. In 1858 the last sheets of the 'Cosmos'
were put into the publisher's hands, but Humboldt did not

CH. XXXVII. DEA TH OF HUMBOLDT. 387

live to see them finished. He had done his part : the work
he had proposed to himself was completed, and he fell
peacefully asleep on the 6th of May, 1859.

Chief Works consulted. — Goethe's * CEuvres Scientifiques ;' Faivre ;
Asa Gray's * Botany ; ' L. Agassiz's ' Centenary Address on A. von
Humboldt ; ' Humboldt's * Cosmos. '

NINETEENTH CENTURY. pt. hi.

CHAPTER XXXVIII.

SCIENCE OF THE NINETEENTH CENTURY (CONTINUED).

The three Naturalists, Lamarck, Cuvier, and Geoffroy St.-Hilaire —
Cuvier begins the Museum of Comparative Anatomy — Lamarck's .
History of Invertebrate Animals — Geoffroy St.-Hilaire brings Natural
History Collections from Egypt — Lamarck on the Development of
Animals — Geoffroy St.-Hilaire on * Homology,' or the similarity in
the parts of different Animals — Cuvier's *Regne Animal,' and his
Classification of Animals — Cuvier on the perfect agreement between
the different parts of an Animal — He studies and restores the re-
mains of Fossil Animals — His * Ossemens Fossiles ' — Death of
Cuvier — Von Baer on the study of Embryology — His History of the
Development of Animals, 1828.

Lamarck — Cuvier — St.-Hilaire. — When Humboldt visited
Paris in 1804 there were three men holding professorships j
in the Museum of Natural History in that city, who had \
afterwards a great influence upon the study of the science j
of living beings. These three men were Lamarck, pro- j
fessor of zoology ; Geoffroy St.-Hilaire, his fellow-professor ;
and Cuvier, assistant-professor of comparative anatomy.

The early part of the nineteenth century was, as you
will remember, a very troubled time for France. The first
Napoleon was carrying war and desolation all over Europe,
and Paris was kept in a constant state of turmoil for many
years. During all this time it is interesting to see how
steadily and quietly the three men I have mentioned pur-
sued their search after knowledge. Geoffroy St.-Hilaire

CH. XXXVIII. LAMARCK— CUVIER. 389

twice risked his life in saving friends from the terrors of the

Revolution; and Cuvier held political appointments both

under Napoleon and under Louis Phihppe ; but in spite of

these duties and interruptions their scientific work was

never neglected ; and a great part of the knowledge about

plants and animals which we now possess was accumulated

during the troublous times of the French revolutions.

Jean Baptiste de Monet, Chevalier de Lamarck, the

elder of these three men, was born in 1 744 at Bezantin, in

Picardy, and a somewhat curious circumstance led him to

devote his life to science. His father intended him for the

church, but the lad had a passion for the army, and on his
»
father's death, in 1760, set off to Germany, where the French

were then fighting, and soon distinguished himself as a volun-
teer. Some time afterwards, however, one of his comrades
lifted him up by his head in joke, and so strained the glands
of the neck that after a very severe illness he was obliged to
give up his profession and become a banker's clerk in Paris.
He had thus time and opportunity to study natural science,
for which he had always had a great liking, and in 1778 he
published a small book on botany. Buffon, who was then
at the height of his fame, was pleased with this work, and
procured for Lamarck an appointment in the botanical de-
partment of the Academic des Sciences. From there he
went to the Jardin des Plantes, and eventually became pro-
fessor of geology in the Musee d'Histoire Naturelle.

George Leopold Cuvier, afterwards made Baron Cuvier by
Louis XVIIL, was bom of Swiss parents at Montbeliard, near
Besangon, in 1769. He, too, was intended for the church,
because his parents were not rich and he had an uncle who
could help him in that profession ; but Prince Charles of
Wurtemberg having heard of his abilities, sent for him and

390 NINETEENTH CENTURY. pt. hi.

gave him a free education in the Acadeinie Caroline at the
University of Stuttgard. Here he already began in his spare
moments to read books of natural history and make drawings
of plants and animals. When he left Stuttgard he went as
tutor in a nobleman's family at Caen, in Normandy, and found
a new and delightful study in the examination of the marine
animals on the sea-shore. After living there six years, he
happened to meet the celebrated Abbe Tessier, who had fled
from the Revolution in Paris, and through his means the young
Cuvier was introduced to Geoffroy St.-Hilaire and other
scientific men in Paris, and became assistant-professor of
comparative anatomy in the Jardin des Plantes. From this
post he rose to very great honours both as a politician and
man of science, holding the posts of President of the In-
stitute, Inspector- General of Education, Councillor of the
Imperial University, and many others of equal importance.

Geoffroy St.-Hilaire, the third and youngest of the three
friends, was born at Etampes in 1772. It is curious that he
also began his education as a priest, and that all these
three men should have given up the church for science.
In St.-Hilaire's case it was a passionate love for zoology
which led him to persuade his father to let him stop in Paris
to study at the Jardin des Plantes, where he was soon
offered a post which gave him an excuse for following his
own tastes. He afterwards joined Lamarck at the Musee
d'Histoire Naturelle in 1793 ; and in 1795 it was chiefly
through his influence that Cuvier was invited to Paris and
became their fellow-worker.

It now remains for us to see what was done by these
three remarkable men. For three years they all remained at
work in the museum. Cuvier had found in a lumber-room
four or five old skeletons collected by Daubenton (p. 205),

CH. XXXVIII. DEVELOPMENT OF ANIMALS. 391

and he determined to make them the beginning of a mu-
seum of comparative anatomy, which afterwards became
very famous. St.-Hilaire worked with Cuvier, while Lamarck
began the study of those animals — such as insects, snails,"
worms, shell-fish, sea-anemones, and sponges — which have
no backbone, and to which he first gave the name of ' in-
vertebrate animals.' Lamarck's work on these animals is
one of the most famous he ever wrote.

In 1798 Cuvier and St.-Hiliare were both invited by
Napoleon I. to go with the French army to Egypt and
study the curiosities of natural history which were to be
found there. Cuvier declined, but St.-Hilaire went, and
spent three years examining the embalmed animals of the
Egyptians. He succeeded in 1801 in bringing away the
beautiful collections of these and other relics from Alexan-
dria, when the French were forced to give up the town to
the English. These collections were conveyed safely to the
Museum in Paris in 1802.

Lamarck on the Development of Animals, 1801. — Mean-
while Lamarck published in 1801 a little work on the
' Organization of Living Bodies,' and in it he first suggested
that the different animals were not created separately, but
had been gradually altered from a few simple living forms,
so that, in the course of long ages, there had sprung up an
immense variety of species of animals in the world. It must
be remembered that Lamarc!^ had chiefly studied plants and
the lower animals. We have seen how Goethe showed that
all plants are only altered stems and leaves \ and the lower
animals, such as jelly-fish, snails, and worms, differ much
less from each other than the higher animals do. There-
fore Lamarck was very much struck with the difficulty there
was in settling which were distinct forms or species, and

392 NINETEENTH CENTURY. pt. hi.

which might have come from the same parent, and he con-
cluded that the only difference was that some had branched
off from the common stock earlier than others, and so had
become rnore unlike — ^just as brothers and sisters are very
like each other while distant cousins are much less liable to
have the same features and expression.

The more we know of animals and plants, said La-
marck, the more difficult we find it to settle which are
related to each other and which are not. Linnaeus had long
ago pointed out that among plants which are well known,
such as the willows in Europe, the cactuses in South
America, and the heaths and everlastings at the Cape, there
are so many kinds differing very little from each other that it
is impossible to say which ought to be considered as separate
species and which as the descendants of one kind of plant.

Moreover, we know how much plants and animals are
sometimes altered even in a few years. For example, by
growing in a drier soil or up a high mountain, plants
become stunted and altered in many ways, while birds when
shut up lose the power of using their wings, as has been the
case with our domestic poultry. Man can make a number
of different varieties both of plants and animals by merely
keeping those which have the peculiarities he admires. The
different kinds of pigeon, for example — the pouters, fan-tails,
tumblers, and others, which are so unlike each other— are
said by naturalists to be all descendants of the common
rock-pigeon ; and all the varieties of rabbit have come from
one wild species. You cannot find a wild pigeon with a
fan-tail, or a wild rabbit with lop-ears.

If man, then, in a few hundred years can make such
changes, ' is it not possible,' said Lamarck, ' that nature in
all the long ages during which the world has existed, may

CH. xxxvni. MODIFICATION OF ORGANS. 393

have produced the different kinds of plants and animals by
gradually enlarging one part and diminishing another to suit
the wants of each ? ' These and many other arguments
Lamarck brought forward in his work in 1801, and again in
his ' Philosophie Zoologique ' in 1809, to prove that the way
in which the Creator has formed different plants and animals
has been by altering them gradually out of simple forms.

There was, however, one very weak point in all his cugu-
ments ; he did not show sufficiently what should cause living
beings to go on altering, and becoming more and more dif-
ferent. For if' you turn plants and animals, which man has
altered, out into the fields again, in a very few generations
they return very nearly to their old forms ; nor can we see
any reason why the differences between animals should go
on increasing unless they were picked out and kept apart,
as men keep them when they want to get new varieties.

Lamarck did, indeed, point out that climate and dif-
ference of food would help to alter the nature of an animal,
but the chief reason he gave for changes taking place in
them, was that the animal itself might cause the alteration in
its form 3 as for instance, a giraffe constantly wishing to eat the
boughs off high trees might stretch his neck, and so by de-
grees each generation might have longer necks than the last
one. This reason was so weak and ridiculous that it prevented
naturalists from paying much attention to Lamarck's theory.

Geoffroy St.-Hilaire points out that the Parts or
Organs are the same in all Animals, only Modified to
suit their Wants. — Nevertheless Geoffroy St.-Hilaire was
inclined to think there was some truth in this theory, although
Cuvier was strongly against it. Cuvier, you remember, had
given his time chiefly to the restoration of the skeletons of
the higher animals, and he was as much struck with the im-

394 • NINETEENTH CENTURY. pt. iir.

mense difference between them, as Lamarck had been with
the Hkeness of the lower animals. Cuvier thought that each
animal was at first created separately, and all its parts were
arranged expressly to meet its wants. He looked upon the
creation of each kind of animal as the making of a machine,
where we put a wheel here and a valve there expressly to
make it do the work required.

Geoffroy St.-Hilaire, on the contrary, insisted that we
never find any part of an animal which we can say was made
expressly for it. Whenever we examine it closely enough
we find it is exactly the same as exists in other beings, only
its growth is altered so as to make it useful to that particular
animal. The pouch of the Kangaroo, he said, is only a fold
of the skin which is looser than in other animals ; the trimk
of the elephant is a nose which has become extremely long ;
the hand of a man, the leg of a horse, and the wing of a
bat, are the same organ and have the same bones, although
they serve such different purposes. ' Nature,' he said, ' has
formed all living beings on one plan, essentially the same in
principle, but varied in a thousand ways in all the minor
parts j all the differences are only a complication and
modification of the same organs.'

This similarity of structure, or homology as it is called,
which runs through all animals, was thus first clearly stated
by St.-Hilaire, and it has now been most carefully worked
out and confirmed by our living anatomists. Yet Cuvier op-
posed it to the last, for his mind was full, as we shall see
presently, of another idea which is equally true ; namely, how
perfectly each part of an animal is made to fit all the other
parts of his body ; and it seemed to him impossible that this
could be, unless each part was created expressly for the work
it had to do.

CH. XXX.VIII. CUVIERS VIEWS. 395

The discussion between the two friends became so
animated that all Europe was excited by it. It is said that
Goethe, then an old man of seventy-one, meeting a friend,
exclaimed, ' Well what do you think of this great event ? the
volcano has burst forth, all is in flames.' His friend thought
he spoke of the French Revolution, and answered ac-
cordingly. ' You do not understand me,' said Goethe, ' I
speak of the discussion between Cuvier and St.-Hilaire: the
matter is of the highest importance. The method of looking
at nature which St.-Hilaire has introduced can never now be
lost sight of again.' And he was right, for the doctrine of
homology, as taught by St.-Hilaire, is one of the strongest
arguments for the theory of the development of living
beings, now held by all the most able naturalists, and of
which we shall speak in Chapter XL.

Cuvier proves that the Parts of an Animal agree so
exactly that from seeing one Fragment the Whole can be
known. — We have seen that Cuvier did not agree with
many of the views of Lamarck and St.-Hilaire. We must
now consider what work he did himself ; for though all the
three friends laboured well, Cuvier accomplished the most of
all. He had a most remarkable capacity for work ; we find
him at the same time restoring skeletons and studying each
bone with minute care, lecturing to large bodies of students,
writing the history of all the sciences, and examining fossils
from the rocks ; besides presiding over councils and superin-
tending national education. And whatever he touched was
done thoroughly and with a master-hand.

His first great work was to collect all the different facts
of comparative anatomy established since the time of
Hunter, and, adding a great mass of his own observations, to
build them up into one complete science of anatomy. In

396 NINETEENTH CENTURY. pt. hi.

his 'Regne Animal/ published in 1817, he made a new
classification of the whole animal kingdom, dividing them
into four great branches. The vertehrata, or animals with
back-bones ; the molhisca, or soft-bodied animals, such as
snails ; the arttatlata, or animals, such as crabs, spiders, bees,
and ants, whose bodies are composed of movable parts,
hardest outside, and jointed or articulated together ; and
the radiata, or animals whose parts are arranged round an
axis, such as star-fish and polyps. These four branches
he divided again • into classes, orders, families, genera, and
species, making a much more complete classification than
Linnseus had done, because it was founded more upon the
internal structure of animals.

In this work he pointed out that the parts of an animal
are made to fit to each in such a wonderful manner, that
if only a few bones are placed in the hands of an ana-
tomist he ought to be able to tell you exactly what all the
other bones must be. You will remember that Hunter
had hinted at this when he showed how the teeth of each
species of animal are fitted to the kind of stomach into
which the food is to pass. But Cuvier proved that this is
true not only of the teeth but of every bone in the skeleton
of an animal.

' Every organized being,' he says, ' forms a whole and
entire system . . . none of its parts can change without a
change of the others also. Thus, if the stomach of an
animal is made so as only to digest fresh flesh, his jaws
must be formed to devour the prey, his claws to seize and
tear it, his teeth to divide the flesh, and the whole system of
his organs of motion to follow and overtake it. Nature
must even have planted in his brain the necessary instinct to
hide himself and lay snares for his victim. These are the

CH. XXXVIII. CUVIER ON FOSSIL ANIMALS. 397

general conditions of a carnivorous life, and all animals who
are to live this life must fulfil them, otherwise they cannot
exist. And besides these general conditions there are
special ones, according to the particular kind of life the
animal has to live, and each of these require modifications
in the form of the organs ; so that not only the class, but the
order, the genus, and even the species of an animal are
revealed by each part of it.'

And now you will understand why Cuvier could not
believe St.-Hilaire's theory that all the parts of one class of
animals— such as the vertebrate animals, for example— are
made on one model, and that when some organ has to play
a different part it is altered, and not created for the purpose.
Cuvier was strongly impressed with the beautiful agreement
in every part of each particular animal, which enables it to
provide for all its wants ; while St.-Hilaire was equally im-
pressed with the general agreement between the structure of
all animals in any one great class. Both these views were
true, but in the state of knowledge at that time it was very
difficult to reconcile them. You must bear this in mind,
because it is one of the difliculties upon which light is thrown
by Mr. Darwin's observations, which we shall examine
by-and-by.

Cuvier Studies and Restores the Remains of Fossil
Animals, 1812- — We have seen that Cuvier's knowledge of
the agreement between the different parts of an animal was
so great that from even one bone he could tell what the other
parts of the body must be. The use which he made of this
knowledge enabled him to reveal a wonderful history about
the fossils buried in the crust of our earth.

When he first came to Paris, and for many years after-
wards, a number of skeletons and parts of skeletons of ani-

39S NINETEENTH CENTURY. pt. hi.

mals, were being dug up round about Paris. These were a
great puzzle to anatomists, for the bones were many of them
immensely large, and none of them seemed to agree exactly
with those of any known animals. Cuvier no sooner heard
of these fossils than he set to work to study them, making
use of his great knowledge of anatomy to sort out the con-
fused mass. His practised eye could detect from among
the heap of bones those which belonged to each other, and
out of a mere handful of fragments he could restore in
imagination the animal from which they must have come.
It was like the work of an enchanter's wand.

' At the voice of comparative anatomy,' he writes, ' each
bone, each fragment, regained its place. I cannot describe
the pleasure I felt in finding that, as I discovered one cha-
racter, all its consequences were gradually brought to light ;
the feet agreed with the history told by the teeth; the bones
of the legs and thighs, and those parts which ought to unite
them, agreed with each other. In a word, each one of the
species sprang from its own fragments.'

And so month after month he worked on, and then to
the great astonishment of naturalists he told them that
all these animals were of species which are found nowhere
upon the earth now. They were all extinct animals. The
greater part belonged to hoofed quadrupeds, something
like our elephant, rhinoceros, and pig j then, there was an
elegant deer-like animal resembling a gazelle, some birds,
some fish, and a kind of opossum, but all these were in
some way different from any which live now.

Here was a history so strange that at first no one would
believe it; for it meant that at the time when the land on which
Paris now stands was being laid down by the rivers, there
must have existed a whole group of animals, all of them

CH. XXXVIII. LES OSSEMENS FOSSILES. 399

more or less different from our present species of animals,
which had not then begun to exist. It had long been
known that strange shells were found buried in the earth's
crust, but then naturalists could never be sure that some
like them might not be living in other parts of the world
without our knowing it, and they had always believed
that at least the larger animals had been created . quite
recently at the same time as man. But here were ani-
mals which no one had ever seen upon the earth, and
it was impossible to suppose that fifty different kinds of
creatures of all sizes, some bigger than an elephant, could be
roaming about the world unseen by anyone. Therefore
there could be no doubt that long before the time of history
or tradition strange animals must have lived and died, and
have been buried in the deposits now forming part of the
earth's crust.

And when this was once recognised, and attention was
called to these buried animals, little by little other forms
were found in older rocks in different parts of the world,
which appeared to be less and less like living animals the
older the rocks were in which they were found. All these
Cuvier described in his famous work called * Les Ossemens
Fossiles,' which he published in 18 12, and in which he laid
before the world a startling history of the long succession of
different animals which must have lived in past ages upon
the earth.

' And here we must close this very imperfect sketch of the
work done by the three French naturalists. You ought
chiefly to remember about them that Lamarck suggested
that animals have been developed out of a few simple forms;
that St.-Hilaire proved that animals of one class are
formed on the same general plan, similar parts being altered

400 NINETEENTH CENTURY. pt. hi.

to serve different purposes in different animals; and that
Cuvier showed that each part of an animal agrees with the
rest so perfectly that from a i^\f bones it is possible to tell
exactly what animals had lived and died in past ages.

Geoffroy St-.Hilaire outlived both his friends, and died in
1840. Lamarck had died in 1829, in his eighty- fifth year,
having been blind for many years. Cuvier died on May 13,
1832. On the Tuesday previous he had begun his third course
of lectures on Natural Science at the College de France, and
had promised to give in that course his idea of creation, and
how the Divine Intelligence is to be traced through all the
operations of nature j but the promise remained unfulfilled ;
that same evening paralysis set in, and on the next Sunday
he died in his arm-chair as if he had fallen asleep. He had
begged to be buried privately, but that was impossible ; on
hearing of his death men of science flocked from all parts to
do him the last honour, and his pupils bore him to the grave.

Von Baer, the Founder of the Study of Embryology.
1828. — We must not leave this question of the structure of
animals without noticing in passing a new and important study
which began about this time. This was the study of embryo-
logy, or of animals in the earliest stages of their life, as in the
case of the chicken before it leaves the egg. You know that
if you take a bird's &gg when it is newly laid, you will see
inside it a yellow yolk floating in a white fluid. But if you
take the egg after the mother-bird has sat upon it for some
days, the yolk will begin to have the form of a bird, and if
you were to take a dozen eggs of one brood of chickens and
crack one every few days while the mother was sitting upon
them, each one would be more like a chicken than the last,
until the twelfth, if you opened it just about the time when it
ought to be hatched, would be a perfect chicken, only that its

CH. XXXVIII. VON BAER— EMBRYOLOGY. 401

feathers would not be yet grown. Now the study of the
different stages of the development of the chicken in the
Q,gg., and of all living beings going througli the same stages, is
called E?nbryology, and has become of immense importance
in the history of animals.

You will remember that Harvey, Malpighi, and many
other physiologists, occupied themselves with this study ;
but no discoveries of very great importance were made in
it before the time of Karl von Baer, a Russian anatomist,
who was born in 1792, Von Baer was the pupil of a very
famous anatomist. Professor Dollinger, and while he was
working under him at Wiirzburg he made for him a
number of observations upon the growth of the chicken
in the Qgg, which led him to study the embryology of
animals, and to discover the remarkable law of which we
must now speak.

Before Von Baer's time it had always been supposed that
the many kinds of animals, so different from each other,
must be quite unlike from the very first moment that they
began to grow, but Von Baer discovered that this is not so,
but that the embrj^os or beginnings of an ox, a bird, a lizard,
or a fish, are so like each other that they can only be dis-
tinguished by their size ; and, what is still more remarkable,
they remain alike till they have been growing for some time.
For example, if you could watch the beginning of these four
animals, there would be a certain time during which you
could see no difference in their form. Then after a while
the fish would start off on a road of its own, but still the
other three would go on all alike. Then, when they had
grown a little bigger, the lizard would branch off, and only
the bird and the ox would continue to have the same

402 NINETEENTH CENTURY, pt. hi.

form, until lastly the bird would take on its own peculiar
shape, and the ox would go on alone, having passed through
the same stages as the fish, the reptile, and the bird, before
it began to shape itself like a mammal. You must notice
carefully that this does not mean that the beginning of an
ox is at any time like a full-grown fish, which is a mistake
that people often make j but only that there is a time when
the embryos of these animals follow exactly the same plan.

You will see, if you consider for a moment, that the dis-
covery of this curious fact gave naturalists a new and much
more perfect way of classifying animals; for they could
actually read the history of an animal by watching it in the
earlier stages of its growth and seeing at what point it
branched off and put on special peculiarities of its own j and
in some of the lower and more obscure animals several mis-
takes of classification were corrected by this means. There
was also another very important question settled by Von
Baer's law. It proved that St.-Hilaire was certainly right in
saying that animals are formed on one plan, having special
parts altered to suit their wants, for here in the embryo those
parts can be seen actually developing differently in different
animals out of the same beginnings. The study of em-
bryology has been carried to great perfection since Von Baer
published his ' History of the Development of Animals ' in
1828; but though many names are better known than his in
connection with it, still it should always be remembered that
he was the discoverer of the law of embryological develop-
ment.

Chief Works consulted. — Goethe's 'CEuvres Scientifiques,' Faivre,
1862; Asa Gray's 'Botany,' 1858; L. Agassiz's ' Centenary Address
on A. von Humboldt,' 1869 ; HumlDoldt's 'Cosmos;' *Biog. Univer-

CH. XXXVIII, EMBRYOLOGY. 403

selle' — Cuvier, GeofFroy St. -Hilaire, and Lamarck ; Lamarck's 'Philo-
sophic Zoologique;' Cuvier's ' Ossemens Fossiles;' GeofFroy St. -
Hilaire's ' Zoologie Generale Suites a Buffon ; ' * Vie et Travaux de
G. St. -Hilaire;' Flom-ens' 'Eloge de Cuvier;' 'Miscellany of Nat.
Hist. ' — Lauder's * Memoir of Cuvier ; ' Jardine's ' Naturalist's Library
Memoir of Lamarck ; ' Huxley on Von Baer — Appendix to Baden
Powell's ' Unity of Worlds ; ' Agassiz's ' Systems of Classification.'

404 NINETEENTH CENTURY. pt. iit.

CHAPTER XXXIX.

SCIENCE OF THE NINETEENTH CENTURY (CONTINUED).

Prejudices which retarded the Study of Geology — Sir Charles Lyell
traces out the Changes now going on — Mud carried down by the
Ganges — Eating away of Sea -coasts — Eruption of Skaptar Jokul —
Earthquake of Calabria — Rise and fall of Land — 'Principles of
Geology' published in 1830 — Louis Agassiz : his Early Life —
De Saussure's Study of Glaciers — Agassiz on Europe and North
America being once covered with Ice — Boucher de Perthes on
ancient Flint Implements — MacEnery on Flint Implements in Kent's
Cavern, with Bones of Extinct Animals — Swiss Lake-dwellings —
' Antiquity of Man.'

In 181 1, when Cuvier published his work on * Fossil Re-
mains/ William Smith, who, as you remember (p. 233), first
studied the rocks of England, had nearly completed his
geological map, and scientific men were beginning, both in
England and Germany, to understand something of the dif-
ferent ages of the "formations which have been laid down
from time to time on the surface of the globe ; yet still they
were prevented from reading the past history of the world
rightly, by several false notions which continued to prevail.

People had so long held the belief that our earth had
only existed a few thousand years, that when geologists
began to find great numbers of strange plants and animals
buried in the earth's crust, immense thicknesses of rock
laid down by water, and whole mountain-masses which must

CH. XXXIX. SIjR CHARLES LYRLL. 405

have been poured out by volcanoes, they could not believe
that this had been done gradually and only in parts of the
world at a time, as the Nile and the Ganges are now carry-
ing down earth to the sea, and Vesuvius, Etna, and Hecla
are pouring out lava a few feet thick every year. They still
imagined that in past ages there must have been mighty
convulsions from time to time, vast floods swallowing up
plants and animals several times since the world was made,
violent earthquakes and outbursts from volcanoes shaking
the whole of Europe, forcing up mountains, and breaking
open valleys. It seemed to them that in those times when
the face of the earth was carved out into mountains and
valleys, table lands and deserts, and when the rocks were
broken, tilted up, and bent, things must have been very
different from what they are now. And so they made im-
aginary pictures of how Nature had worked, instead of
reasoning from what they could see happening around
them.

Sir Charles lyell teaches that the Rocks of our Earth
have been formed by Natural Causes, such as are still
going on, 1830. — The man who first broke through these
prejudices was our great geologist. Sir Charles Lyell, who
has only just now passed away from among us. Charles
Lyell was born in Forfarshire, in 1797, the same year that
Hutton died. From his earliest childhood he had a great
love of Natural History and Science, but as his father
wished him to become a barrister, he went to Oxford to
follow the usual course. Here he attended the lectures of
Dr. Buckland, the great geologist of that day, and this de-
cided him to devote his life to the study of geology. He
began first by examining the formations round about his
own home in Forfarshire, and he soon became convinced,

406 NINETEENTH CENTURY. pt. ill.

as Hutton had been before him (see p. 219), that we can
only learn the past history of the earth by observing the
causes now at work.

What Hutton had suggested Lyell worked out. He col-
lected with great care all that is known of changes going on
now all over the world, and the causes which produce them.
Among these were —

istly. The fall of rain, and how it wears away the earth
and carries it off in little rills to the river.

2ndly. The amount of mud carried by mighty streams,
such as the Ganges, the Nile, and the Mississippi, and laid
down in the sea at their mouths.

3rdly. The amount of lime, iron, and other minerals
brought up by springs from the inside of the earth, and
thrown down on the surface.

4thly. The tides and currents of the sea, and how they
wash up fresh land on some coasts and eat away th^ land
on others.

5thly. The growth of corals in the sea, and how remains
of their skeletons become cemented into limestone.

6thly. The volcanoes which are throwing out lava, and
how much they have thrown out in historical times.

7thly. The different earthquakes which man has wit-
nessed, how they have broken and dislocated the land,
raising it in some places, as in New Zealand, and causing
it to sink in others, as at New Madrid, in America.

8thly. The way in which plants and animals are buried
in the mud of lakes, or at the mouths of rivers, or in peat and
sand.

All these, and many other changes which are taking
place all over the world in the present day, Lyell studied
with great accuracy, and then began a book to show that

cii. XXXIX. SIR CHARLES LYELL. 407

what we find in the rocks might all have been produced by
such causes as these, without imagining any extraordinary
violence of nature.

While writing this book he went with another celebrated
geologist, Murchison, to Italy and Sicily, and there he
studied not only the rocks which the volcanoes of Vesuvius
and Etna have been building up for ages, but he also saw
at Syracuse and other places enormous beds of limestone
filled with shells of kinds which may still be found living.
The immense thickness of these limestone beds, amounting
in some places to 700 and 800 feet, astonished him greatly.
He knew they must all have been formed slowly beneath
the sea, out of the remains of corals and other animals,
whose skeletons or shells are composed of lime, and that
they must afterwards have been raised up to the height of
3,000 feet above the sea, at which he found them; and
when he thought of the time which this must have taken,
and Remembered that it had all happened since the other
great masses of rocks below, containing extinct shells, had
been formed, he felt more than ever convinced that the world
must be very old, to have allowed time for all the wonderful
changes that have taken place.

In 1830 his book was published, and though it met with
great opposition because men's minds were prejudiced the
other way, yet his facts could not be denied. He showed,
for example, on the one hand that the river Ganges in India
carries down every year, and deposits in the sea, as much
mud as would make sixty of the great pyramids of Egypt,
and which if it was brought in ships would require 2,000
full- sized merchant vessels laden with mud to sail down the
Ganges every day. Here, then, was an example of rocks
being now laid down in the sea, not by violent floods and

408 NINETEENTH CENTURY. pt. hi.

sudden catastrophes, but so quietly that no one even notices
that nature is at work.

Then, on the other hand, he pointed out how in our own
little island, on the coasts of Yorkshire. and Norfolk, the sea
eats away the cliffs, so that towns such as Auburn, Hartbum,
and Hyde in Yorkshire, which are marked upon old maps,
have been entirely washed away, and the ground on which
they stood has been spread out on the bottom of the ocean ;
and yet this is done so gradually, year by year, that new
towns of the same name are built up farther inland, and no
one disturbs themselves about the loss.

Then to. account for the huge masses of basalt and lava
which are found in the earth's crust, he reminded his readers
of the great eruption of the volcano called Skaptar Jokul in
Iceland, which took place in 1783. In this eruption the
torrent of lava was ninety miles in length, from seven to
fifteen miles in breadth, and in some places 600 feet deep,
and the whole mass poured out would have made a mountain
as big as Mont Blanc.

He then went on to give accounts of the remarkable
earthquakes which have taken place in times of history :
the earthquakes in India, in Java, and especially in Cala-
bria, in 1783, when new lakes were formed by the sinking
in of the ground, and the rivers were made to run in new
channels. He showed also how the height of land is some-
times changed in volcanic countries j as on the coast of
Italy, near Naples, where the ground on which the famous
Temple of Serapis stands can be proved to have been
raised and depressed twice even in historical times.

And besides all these obvious changes which men cannot
help noticing, he proved that other quiet and unnoticed risings
and fallings of land are taking place ; as, for example, in Nor-
way and Sweden, where the land is rising out of the sea in

cir. XXXIX. SIR CHARLES LYELL. 409

some places at the rate of about two or three feet in a cen-
tury ; and in Greenland, where it is sinking, so that huts
built near the shore have to be moved inland because they
are becoming submerged in the sea.

These are a very few of the facts which you can under-
stand, by which Lyell demonstrated that the surface of our
earth is always undergoing changes in our own day, and that
by similar changes going on in past times the whole of the
crust of our earth may have been built up and carved out.
In addition to this he showed how plants and animals are now
being buried in mud and earth, and how their remains are
washed into caves, or preserved in peat-mosses ; thus afford-
ing us examples of the way in which the remains of ancient
animals have become entombed in the earth's crust.

Thus Sir Charles Lyell taught men to read the true his-
tory of the earth. It is difficult in the present day to under-
stand rightly how great a work he accomplished, for though
his ideas were ridiculed in the beginning, yet he lived long
enough to see all men agree with him, and his doctrines
received as self-evident truths. Like all other great men,
he was humble and reverent in his study of nature. His
one great desire was to arrive at truth, and by his con-
scientious and dispassionate writings he did much to per-
suade people to study geology calmly and wisely, instead
of mixing it up with angry disputes, like those which, in
the time of Galileo, disfigured astronomy. He travelled
a great deal, especially in America, and worked out a great
many facts in geology. But in future ages his name will
stand out among those of other geologists chiefly as having
shown that the changes in the crust of our eai'th have been
brought about in the cou7'se of long ages by causes like those
which are still in action.

After the year 1830, when his ' Principles of Geology '
19

4IO NINETEENTH CENTURY. pt. hi.

was first published, the study of this science went on very
rapidly indeed. As with all the other sciences of the nine-,
teenth century, you must read the details in special works ;
but there are two great discoveries which we must mention
very shortly here. These are — ist. The fact that much of
temperate Europe, Asia, and America was at one time
covered with ice, as Greenland is now ; and 2nd, that
man has lived upon the earth much longer than was once
supposed.

Louis Agassiz, 1807-1874. — The man whose name will
always be remembered as having first traced out the wonder-
ful history of the great ice-period is Agassiz, the famous
Swiss naturalist, who was bom in 1807 at Mottier, near
Neuchatel, and died in 1874 in America.

Louis Agassiz was the son of a Swiss pastor, and he
forms one among many bright examples in the history of
science, of men who cared neither for wealth, advance-
ment, nor ease, but for the study of nature alone, and the
grand truths to be obtained by it. After receiving a good
education in the Swiss and German Universities, living
frugally and economically, -as students can on the Continent,
he took his degree of Doctor of Medicine at Munich in
1829, having already written several important papers on
zoology. In 1832 he was made Professor of Natural His-
tory at the University of Neuchatel \ and in 1833 he pub-
lished his work on '■ Fossil Fishes,' the expenses of the book
being liberally paid by Humboldt. In 1839 he published
his grand work on the * Fresh-water Fishes of Europe,*
which cost him so much that he was very poor for years
afterwards.

There are very touching passages in some of Agassiz's
private letters at this early period, when he had a hard

CH. XXXIX. AGASSIZ. 411

struggle with life. His enthusiasm breathes out so natu-
rally, and he speaks so regretfully of want of money, not
for himself, but the work he longed to complete ; while
his gratitude is so sensible and heartfelt towards those who
helped him to bring out these splendid additions to the
science of zoology. His was a warm-hearted, earnest, and
active nature, and he was beloved by all who knew him.
It is pleasant to think that the Americans, among whom
he spent the latter half of his life, from 1846 to 1874, ap-
preciated him fully ; so much so that Mr. Anderson, a
rich tobacco merchant of New York, presented him in
1873 with the island of Penikese, one of the Elizabeth
islands, north of New York, and with funds to establish
there a marine naturalist's school. The last year of Agassiz's
life was spent chiefly on this island, training up a group of
young naturalists.

Agassiz proves that parts of northern Europe and
North America must once have been covered with Great
Fields of Ice, 1840. — It is, however, of the early part of
Agassiz's life, while he was still in Switzerland, that we must
now speak. Although his chief study was zoology, yet he
could not live at Neuchatel, and travel about the Alps without
being struck with those mighty rivers of ice, called glaciers,
which creep slowly down the valley of the Alps in Switzerland,
carrying with them stones and rubbish. (See Fig. 62, p. 412.)

These glaciers are formed by the snow, which collects
on the tops of high mountains, and sliding down, becomes
pressed more and more firmly together as it descends into
the valleys, until it is moulded into solid ice, creeping
slowly onwards between the mountains, and carrying with it
sand, stones, and often huge pieces of rock which fall upon
it. At last one end of this ice-river reaches a point where

412

NINETEENTH CENTURY.

PT. III.

f

the air is warm enough to melt it, and here it flows gradually
away as water, leaving the stones and rubbish it has brought
down lying in a confused heap, which is called a moraine.

Towards the end of the eighteenth century a famous
geologist, named De Saussure, spent much time in examining

Fig. 62.

Glacier carrying down Stones and Rubbish (Lyell).

the glaciers of the Alps, and pointed out how they are now
forming large deposits in the valleys, out of these heaps of
rubbish which they bring down from the mountains. Since
his time many geologists had taken up the study, but it was
Professor Agassiz who first spelled out the wonderful history
we can learn from it, about the former climate of our hemi-
sphere. He noticed that rocks over which a glacier has

CPi. XXXIX. GLACIERS. 413

moved, are polished and grooved by the rough stones and
sand frozen into the bottom of the ice, just in the same way
as a piece of wood is scraped by the sharp iron at the
bottom of a plane ; and by these glacial scratches, or stri(B,
as they are called, he could tell where glaciers had been,
even though there was nothing else to show that ice had
ever existed in the country.

Now, when he began to examine the slopes of the Alps
many hundred feet above the present glaciers, and also in
places where it is now too hot for ice to remain, he found
to his surprise numbers of these glacial striae and also
remains of huge moraines, showing that the glaciers of
olden time must once have been much larger and have
stretched farther down the valley than they do now. And
what was still more strange, these same marks were to be
seen on the Jura Mountains, on the other side of Switzerland,
where there are never any glaciers at present ; moreover, on
the Jura there were found huge blocks, some of them as
big as cottages, which were not made of the same materials
as the hills on which they rested, but were broken pieces of
rock such as are now only found on the Alps.

It was clear, then, that these enormous pieces of stone
must have been carried right across Switzerland from the Alps
near Mont Blanc, and across the lake of Geneva, which is
1,000 feet deep, and then deposited on the Jura range near
Neuchatel, where one block of Alpine gneiss, called the
Pierre-a-Bot, as large as a good-sized cottage, sits perched
on a mountain 600 feet above the top of the lake. How
had these blocks travelled across the Swiss plains ? No flood
could have carried them, for they were too heavy, and be-
sides they were not smooth as stones are which have been
rolled in water, but were rough with sharp edges. Agassiz

414 NINETEENTH CENTURY. pt. in.

was convinced, therefore, that they must have been carried
by ice, and that huge glaciers must once have come down
from the high Alps right across Switzerland, filling the lake
of Geneva with ice, and carrying these blocks with them, as
modern glaciers do now in the Swiss valleys.

This was a marvellous history, for it showed that all the
lower land of Switzerland must once have beeu buried in
ice, but other facts afterwards came to light which were more
wonderful still. In 1840 Professor Agassiz came over to
visit Great Britain, and when he went to Scotland with Dr.
Buckland his practised eye discovered at once in the High-
lands glacial scratchings, remains of moraines, and blocks
which had been carried by ice; and soon it became evi-
dent that these were not confined to Scotland, for Dr.
Buckland recognised them again in Wales and the North of
England, where moraines and erratic blocks are to be seen
in all parts of the country. So that here, too, in our little
island, there must have been at one time huge glaciers as
large as those now found in the Alps.

Nor was this all ; for when once geologists knew where
to look for these signs of glaciers, it began to be discovered
little by little that parts of all the northern countries of
Europe, Norway, Sweden, Russia, Germany, Switzerland,
Northern Italy, England, and even on the other side of the
Atlantic, Canada and North America, have been smoothed
and scratched ; and huge erratic (or wandering) blocks have
been scattered over them, showing that in very remote ages
(yet still while very nearly the same kinds of plants and
animals as now were living upon the globe), the temperate
parts of our northern hemisphere must have been intensely
cold, causing a large part of these countries to be covered
with great fields of ice, as Greenland is in the present day.

CH. XXXIX. BOUCHER DE PERTHES. 415

And just as we see now that icebergs break off from the
Greenland glaciers, carrying with them stones and mud, and
dropping them at the bottom of the sea ; so in those times
icebergs floated over many of the valleys of Europe, which
were then submerged beneath the ocean. You may see in
the railway- cuttings of Wales and in the sea-cliffs in the
coast of Yorkshire and Norfolk huge masses of glacial drift,
as it is called, made of mud and stones confusedly mixed
together, which were dropped from icebergs travelling south-
wards from the ice-fields.

This period of cold is called by geologists the ' Glacial
Period ; ' and when you read works on geology you will see
that it explains in a wonderful manner many curious facts
in the later history of our earth, and the distribution of
plants and animals upon it. For the present it is enough
for you to remember that Agassiz first pointed out the signs
of this cold period, and that this discovery was one of the
earliest rewards of a patient study of causes which are going
on now ; for it is from the ice-action in Switzerland and
Greenland in the present day, that we are able to understand
how these huge ice-fields carried down erratic blocks and
the mud of moraines during the Glacial Period.

Geological Proofs that Man lived upon the Earth in Ages
long gone by, with Animals which are now extinct, 1847.
— The second remarkable discovery which has been made
in geology in this century is that of the antiquity of man; or
the fact that man must have existed upon our earth long
before the very earliest times of history or tradition ; in an
age when an elephant and a hyaena, of extinct species,
roamed about England and France, together with some
other strange animals which are not now to be found upon
the globe.

1

41 6 NINETEENTH CENTURY. pt. hi.

This discovery, which was not believed for a long time,
was first announced by a French geologist, M. Boucher de
Perthes, in the year 1847. It happened that near this
gentleman's house, at Abbeville in Picardy, gravel-pits had
been dug from time to time for repairing the fortifications of
the town, or mending the roads. During these excavations,
in the beginning of the century, a great many bones of ani-
mals had been dug up and sent to Cuvier at Paris ; and he
stated that some of them belonged to animals slightly dif-
ferent from any now living, though not so ancient as those
which came from under Paris (see p. 397). This showed
that these beds of sandstone must have been formed long
before the times of history or the earliest ages in which
man was supposed to have been upon the earth. People,
therefore, were much astonished when M. Boucher de Perthes
stated in 1847 that he had found very rough stone weapons
in these beds, such as savages might use, seeming to prove
that men must have been living at the same time as these
extinct animals.

This seemed so incredible that scientific men would not
even listen to Boucher de Perthes' arguments in his work
called * Antiquites Celtiques,' and it was not till 1858, when
one of our best living geologists, Mr. Prestwich, went to
Abbeville and took a well-shaped flint hatchet out of the
undisturbed gravel with his own hands, that people began to
believe that human beings must have been living in the
world much longer than had hitherto been believed. When,
however, this was once acknowledged to be true, several
new facts sprang up to confirm the theory. Many years
before, in 1825, a Roman Catholic priest, the Rev. J. Mac
Enery, had found flint tools, with the bones of the extinct
elephant, hysena, and bear, in a cave called Kent's Hole,

CH. XXXIX. LAKE-DWELLINGS, 417

near Torquay, but very little notice had been taken of this
discovery. Now, however, they were thoroughly studied,
and they showed clearly that men who made rough flint
tools (such as are still made by savages in many parts of the
world) must have lived in England, together with a bear,
an elephant, a lion, and a hyaena, all of species v/hich have
now ceased to exist.

Discovery of the Swiss Lake- dwellings, 1853.— Again,
in Switzerland, most curious discoveries have been made,
giving us proofs of three distinct periods in the life of man-
kind. In the year 1853, when the Swiss lakes were very
low in consequence of a long drought, WQoden piles were
observed to rise above the water ; and when these were
examined by the Swiss antiquarians it was found that they
were foundations of wooden villages, which had been built
by the inhabitants of Switzerland in past ages. They stood
some way out in the lake, and must have been joined to
the shore by wooden bridges which the villagers could lift
up when enemies came to attack them, and thus become
protected by the water surrounding them. Habitations of
this kind are built in the present day by the natives of Papua
or New Guinea.

Down below the piles in the mud of the Swiss lakes a
great number of tools, cooking utensils, bones of animals, and
even burnt bread and corn, were- found; and the remarkable
thing was, that the" different kinds of tools showed that the
villages did not all belong to one age. In a few, on the
lakes of Bienne and Neuchatel, iron tools were buried, show-
ing that when these villages were inhabited men knew how
to melt iron out of the rocks and make it into tools. These
villages must have been about the time of the Romans.

In others, however, .only bronze tools were found, and

41 8 NINETEENTH CENTURY. pt. hi.

these were much older, because bronze was used long before
iron was discovered. And lastly in some, tools of stone
only have been found, some beautifully polished, but others
rough and rude, showing that the men avIio used them must
have been mere savages like the Australians now ; and yet
the oldest of these lake-villages have no bones of extinct
animals in them, and therefore cannot be so ancient as those
men whose tools were found in the cavern at Torquay and
the sandpits of Abbeville, or as have since been found in
England, Denmark, Germany, America, and indeed in
almost all countries.

It is impossible, without a knowledge of geology, to realise
how very long ago these last-mentioned men must have lived.
But when I tell you that since their tools were buried in the
rocks, there has been time for beds of immense thickness to
be laid down little by little, as the Ganges is laying them
down now ; for parts of the French valleys to be gradually
washed away, and their shape altered ; for rivers to change
their courses, and vast beds of peat to grow over the
bottoms of the valleys ; and, more than all, for whole races
of animals which once lived to have died quite away from
the face of the earth, you may perhaps form some idea of the
long ages that man must have been upon our globe. This
history, however, is so new and as yet so little understood,
that it cannot be explained in a few pages. You will find
all the proofs of it given in Sir Charles Lyell's work on the
* Antiquity of Man,' in which they were first collected in 1863 ;
and you must remember the fact, that man is very ancient,
as one of the great discoveries of the nineteenth century.

CMef Worh consulted. — Lyell's ' Principles of Geology,' 'Elements
of Geology,' ' Antiquity of Man ; ' Lubbock's ' Prehistoric Times ; '
'Quarterly Geological Journal,' vol. xxx. : Obituary of Agassiz.

CH. XL. BIOLOGY.

419

CHAPTER XL.

SCIENCE OF THE NINETEENTH CENTURY (CONTINUED).

Facts which led Naturalists to believe that the Different Kinds of
Animals are descended from Common Ancestors — All Animals
of each Class formed on one Plan — Embryological Structure —
Living and Fossil Animals of a Country resemble each other —
Gradual Succession of Animals on the Globe — Links between Dif-
ferent Species— Darwin's Theory of Natural Selection — Wallace
worked out the same Theory independently — Sketch of the Theory
of Natural Selection — Selection of Animals by Man — Selection by
Natural Causes — Difficulties in Natural History which are explained
by this Theory — Foolish Prejudices against it — Concluding Remarks
on the History of Science.

Facts wMch have led Naturalists to believe that the
different kinds of Animals are descended from common
Ancestors. — We now come to the first attempt of any value
which has ever been made, to explain how the different kinds
of animals and plants have been produced. This question
is so very difficult, and seems so much beyond our grasp,
that we find very few people throughout the history of
science who even tried to answer it. Aristotle, it is true,
remarked that we can trace such a close resemblance
between the different species, from the lowest plant up to
the highest animal, as would seem to show they are related
to each other (p. 16). Bonnet, too, thought that animals
were developed from lower into higher forms (p. 202) ; and
Lamarck, as we have seen, boldly suggested the same expla-
nation (p. 391).

430 NINETEENTH CENTURY. ft. hi.

But people in general treated these as mere wild specu-
lations, and were content to say that God had created
animals, just in the same way as they said that the stars
were created by Him, without pausing to consider how He
has created them.

Since the time of Buff on and Linnseus, however, many
new facts had gradually been brought to light about living
animals ; and fossil species had been dug out of the earth,
showing that many different forms had lived upon our globe,
one after the other j and these new discoveries led naturalists
to speculate whether some clue might not be found to
explain this long succession of living beings.

Then again, as naturalists spread all over the world and
many new forms of animals and plants became known, it was
found to be more and more difficult to separate the different
species and to say which are and which are not descendants
of one parent. Linnaeus, as we have seen (p. 392), pointed
this out in the case of plants, and wild roses are a very good
example of it ; for the different kinds run so much into each
other that while one of our best botanists has divided them
into seventeen s^ecies^ another thinks that many of these must
have come from the same parent, and that only five species
can be distinguished. Again, among insects, the well-known
naturalist, Mr. Bates, has shown that on the Amazons in South
America it is often impossible to tell, among some families
of butterflies, which are the same species and which keep
apart from each other. Facts like these, of the relationship
of living beings, had long been forcing themselves upon
naturalists, and this was one of the reasons given by Lamarck
for supposing animals to be all descended from a few simple
forms.

All the Animals of each Class formed on the same

CH. XL. DESCENT OF ANIMALS. 421

Plan. — Another reason was that curious agreement in the
bones of different animals which had become more and
more noticed ever since the time of John Hunter, and which
Geoffroy St.-Hilaire insisted upon so strongly. Why should
the animals of one class (such as the vertebrate or back-
boned class) be formed all on one plan even to the most
minute bones ; so that the wing of a bat, the front leg of a
horse, the hand of a man, and the flapper of a porpoise, are
all made of the same bones, which have either grown together,
or lengthened and spread apart, according to the purpose
they serve ? And, more curious still, why should some
animals have parts which are of no use to them, but only
seem to be there because other animals of the same class
also have them. Thus the whale has teeth like the other
mammalia, but they never pierce through the gum ; and the
boa- constrictor has the beginnings of hind legs hidden under
its skin, though they never grow out. Here again it seemed
extraordinary, if a boa-constrictor and a whale were created
separately, that they should be made with organs which
are quite useless; while, on the other hand, if they were
descended from the same ancestor as other reptiles and
mammalia who have teeth and hind legs, they might be
supposed to have inherited these organs ; just as, for ex-
ample, a child sometimes has a mole or other mark upon its
body in exactly the same place as its great grandfather had
before it.

Embryos of Animals alike in Structure. — Another still
more remarkable fact was that pointed out by Von Baer,
that the higher animals, such as quadrupeds, before they are
perfectly formed, cannot be distinguished from the embryos
of other and lower animals, such as fish and reptiles. If
animals were created separately why should a dog begin

1

422 NINETEENTH CENTURY. pt. hi.

like a fish, a lizard, and a bird, and have at first parts which
it loses as it grows into its own peculiar form ?

Living Animals of a Country agree with, the Fossil
ones. — These were facts entirely belonging to living creatures,
but now others sprang up about fossil species which were
equally puzzling. We know that certain animals are only
found in particular countries ; kangaroos and pouched ani-
mals, for example, in Australia ; and sloths and armadillos
in South America. Now it is remarkable that all the fossil
quadrupeds in Australia are also pouched animals, though
they are of different kinds and larger in size than those now
living ; and in the same way different species of sloths and
armadillos are found fossil in South America ; while in the
rocks of Europe fossil mammalia are found, only slightly
different in form from those which are living there now.
Naturalists therefore asked themselves again — ' Would it not
seem likely that the living pouched animals of Australia
and the sloths and armadillos of America are the descen-
dants of the dead ones in the rocks, although they have in
the course of long ages become rather different from them j
while oxen, bears, wolves, &c., are also the descendants of
those which are found buried in the rocks of Europe ?

Gradual succession of Animals which have appeared
upon the Globe. — This seemed still more likely as the study
of geology advanced, and it became clear that a gradual suc-
cession of higher and higher animals had appeared upon the
globe. Thus, in the oldest rocks containing fossils, we find no
monkeys, no quadrupeds, no reptiles, no amphibians such
as our frogs, but only shells of marine animals, and a few
bones of fishes, of kinds quite different from those now living.

Then in rocks above these we find the fish becoming
very abundant and varied, and higher still we meet with

CH. XL. SUCCESSION OF ANIMALS. 423

footprints of some animal with feet ; and the bones of an
amphibian, somewhat Hke a frog, are next found. In these
times the fish began to cease to be monarchs of the water, for
a Httle higher up huge swimming reptiles, like our crocodiles
and lizards, but much larger, have left their bones in the
rocks. Next come reptiles with wings, which measure six-
teen feet across from tip to tip, and we must picture these
huge flying lizards, with wings like bats, roaming over the
globe with no higher animals to persecute them.

But they were only to have their turn, for in rocks formed
a little later there appear two skeletons, one of a small crea-
ture half reptile half bird, about the size of a pigeon, and the
other of a real bird with some of its feathers still remaining ;
and in beds of about the same age there occurs the jaw of
a small insect-eating animal something like an ant-eater.
Birds and quadrupeds therefore had now begun to exist, and
soon the bones of pouched animals are found, and then of
mammalia, like our moles and shrews ; and from this time
the reptiles become smaller, as if they were kept down
and gradually destroyed by the higher animals, and the
• quadrupeds become larger and more powerful ; till, in those
beds which Cuvier studied near Paris, we find the gigantic
elephant and rhinoceros-like animals we spoke of before ;
while in beds of about the same age occur the first bones of
monkeys.

This is a very rough sketch of the order in which ani-
mals are found in the earth's crust. The lower kinds first, and
then gradually higher and higher forms as they, come near to
our own time ; and if we could study them more closely you
would see that in rocks nearly of the same age the forms
are always very like each other, while the farther apart the
formations are, the more different are the animals. It is true

424 NINETEEKTH CEiVTURY. pt. hi.

that there are very few close Hnks to be found between fossil
animals ; but when Ave remember that nearly all the rocks in
the earth's crust are made out of others which have been
destroyed, it is scarcely wonderful that so few skeletons
should be found of those that were once buried, and it is
not likely that many of these would be just the intermediate
forms we want. Still some have come to light, for a bird-
reptile has been found in the rocks of Kansas, in America,
which has a skeleton like a bird, but teeth and jaws like a
reptile ; and a reptile has been dug out of the Stonesfield
slate in England, which Mr. Huxley says must have hopped
like a bird, having legs, neck, and a bird-like head, while it
had nevertheless teeth like a reptile. Again, horses have
been found in the rocks of America, which have sepa-
rate toes, and others in which the toes are beginning to
grow together, showing how they may have been gradually
altered into our one-toed horse.

And here again, those who studied fossil animals asked
why these forms should succeed each other, gradually pas-
sing on into the living forms of our own day, which are all
slightly altered copies of these fossils of the rocks ?

How can Plants and Animals have become altered ? —
It was questions such as these which seemed to call for
answers, and to find none except the one proposed by
Lamarck j namely, that the different kinds of animals are
all desceiided from a few simple forms. If this were so, then
it would be quite natural that higher and higher forms should
appear gradually upon the earth, and that the kinds most
alike should follow directly upon each other, those which are
now living being very like their ancestors in the newest
formation in the earth's crust. It would also help us to
understand why animals of the same class should have the

CH. XL. DARWIN'S THEORY, 425

same bones, and why some should have parts remaining in
their body which are no longer of any use ; and lastly, it
would explain why naturalists have so much difficulty in
distinguishing nearly related species.

But though these reasons made it seem very likely that
all animals are only different branches from one stem, yet
this could only be a mere speculation unless some one could
point out what has made them differ so much from each
other. Lamarck, as we have seen, could not do this, and
therefore his suggestion was passed by ; and it was not till
about sixteen years ago that two naturalists, Mr. Darwin and
Mr. Wallace, discovered a law which is certainly true in
itself, and which accounts for many of the facts. Their
theory, which we must now consider, is so new that it has
been opposed on all sides, just as the Copernican theory was
opposed in the sixteenth century, the circulation of the blood
in the seventeenth century, and the theory of combustion,
which overturned phlogiston, in the eighteenth century. We
live in the midst of the discussion about the origin of spe-
cies, and it will only be our great-grandchildren who will be
able to talk of the Darwinian theory in the way in which
we talk of the discoveries of past centuries ; but you ought
at least to understand what this theory is, for it forms an
era in the history of science.

Darwin's Theory that Natural Selection has caused the
various kinds of Plants and Animals to differ widely and
permanently from each other. — The theory of Natural Selec-
tion, or the Darwinian theory as it is often called, has been
chiefly worked out by a great living naturalist, Mr. Charles
Darwin, who was born in 1809. When he was only two-and-
twenty, Mr. Darwin went in her Majesty's ship ' Beagle ' to
survey the coast of South America and sail round the globe j

426 NINETEENTH CENTURY. pt. hi.

and on his return he wrote an account of the geology and
natural history of the countries he had visited. He tells us
himself that even so early as this he noticed many facts
which seemed to him to tlirow light on the difficult question
of the origin of the different species of plants and animals ;
and he spent twenty years carefully collecting in England all
the knowledge he could upon the subject. But he did not
publish it, for he wanted more and more evidence ; and as
Newton waited sixteen years for more convincing proof
before he announced his theory of gravitation, so Mr. Dar-
win would have delayed much longer than he did if a
remarkable circumstance had not obliged him to speak.

It happened that while Mr. Darwin was working in Eng-
land, another great naturalist, Mr. Alfred R. Wallace, who
was then in the Malay Archipelago, also thought that he
had discovered the way in which animals are made to vary
in the course of long ages. He sent home a paper on the
subject, and, though he had never heard of Mr. Darwin's
theory, it was found that he had worked out the same
result, sometimes almost in the same words.

Sir C. Lyell and Dr. Hooker of Kew were so much struck
with the fact that these two men had solved the problem
almost precisely in the same way, that they begged Mr.
Darwin to allow one of his papers, written many years
before, to be published with Mr. Wallace's, and the two
essays were read the same evening, July i, 1858, at the
Linnsean Society. A year later, in November 1859, Mr. Dar-
win's famous work, ' The Origin of Species,' was published.

' The Theory of Natural Selection,' or the choosing out
by natural causes of those plants and animals which are
best fitted to live and multiply, rests upon a few simple facts
which you can understand.

CH. XL. DARWIN'S THEORY. 427

Firstly, all living beings multiply so rapidly that there
would be neither room nor food enough upon the earth for
them if they were all to live ; therefore immense numbers
must die young, and those will live the longest and have
children to follow them who are best fitted for the kind of
life they have to lead.

Secondly, no two living beings are ever exactly alike ;
but children always inherit some of the characters of their
parents, so that if any being has a peculiarity which makes
it better fitted for its life, and consequently lives long and
has a large family, some of its descendants will most likely
inherit that peculiarity.

Now it is not difficult to understand that if useful
peculiarities of different kinds are handed down in this way
from parent to child, those who inherit them will in time
begin to be remarkable for diff"erent qualities. For example,
suppose that in a nest of young birds, one with strong wings
lives and has young because it can fly far and get food,
while another also lives and has young because its feathers
are dark, and the hawks cannot see it in the grass. Then
those descendants of the strong-winged bird which also
have strong wings, will be most likely to live on in each
generation, and will pass on this peculiarity to their children;
while the descendants of the dark-coloured bird will also sur-
vive in each generation exactly in proportion as their plum-
age is adapted to hide them ; and thus the strong-winged
birds and the dark-winged birds will in time become very
different from each other. This is roughly the theory of
' Natural Selection ; ' that nature allows only those animals
to live which in some way escape the dangers which threaten
their neighbours, and thus in time the race becomes altered
to suit the life it has to lead.

428 NINETEENTH CENTURY. pt. hi.

There is only one difficulty. It is clear that the strong-
winged birds must not pair with the dark- winged birds, or
otherwise both peculiarities would come out in the young
birds, and the two kinds would no longer remain distinct.
And this is the one stumbling-block in the theory ; we
have never yet been able to trace out two varieties of an
animal which have become so different that they do not pair
together. You should fix this difficulty firmly in your mind,
because it is almost the only real one we shall meet with.
Mr. Darwin's answer to it is, that we have only watched
plants and animals for such a short time, and even then not
with this idea in our minds, so that we are not likely to
have found a case to help us. It has indeed been observed
that animals, if left free to choose, do often pair with those
which resemble themselves, and do in some cases show a
dislike to those that differ; still this is not proved to be
always the case, and it must be acknowledged to be a
difficulty.

Selection of Animals by Man. — But now setting this
aside, let us see what proof there is that animals vary, and that
they can be picked out, so that any peculiarity may become
stronger in each succeeding generation. The best instance is
in pigeons. All our pigeons come from the common wild
rock-pigeon; and the way in which all our pouters, fan-tails,
barbs, and other pigeons have been produced, is by merely
picking out from the young ones those which had either large
crops, or wider tails, or longer beaks, and pairing them to-
gether, so that the young birds had these peculiarities still
more strongly. The same thing is true of our different kinds
of oxen, sheep, horses, and fowls ; so we see clearly that
different varieties can be produced by choosing out parti-
cular animals. Man does this quickly, because he only

CH. XL, NATURAL SELECTION. 429

attends to one peculiarity, which interests him ; but nature
does it very slowly, because no animal can live unless every
part of it is fitted for its life better than in those which are
killed off.

Selection by Natural Causes. — Now Mr. Wallace has
calculated that one pair of birds having four young ones
a year, would, if all their children, grandchildren, and great-
grandchildren, lived and paired, produce about two thou-
sand million descendants in ffteen years. And Mr. Huxley
tells us that a single plant producing fifty seeds a year would
if unchecked cover the whole globe in nine years, and leave
no room for other plants.

It is clear, therefore, that out of these numbers millions
must die young, and it is only the most fitted in every way
that can live and multiply. One example from Mr. Darwin's
book will show you how complicated the causes are, which
determine what particular kinds shall flourish. He tells us
that the heartsease and the Dutch clover, two common
plants, can only form their seeds when the pollen is carried
from flower to flower by insects. Humble-bees are the only
insects which visit these flowers, therefore if the humble-bees
were destroyed in England there would be no heartsease or
Dutch clover.

Now the common field-mouse destroys the nests of the
humble-bee, so that if there are many field-mice the bees
will be rare, and therefore the heartsease and clover will not
flourish. But again, near the villages there are very few field-
mice, and this is because the cats come out into the fields
and eat them ;' so that where there are many cats there are
few mice and many bees, and plenty of heartsease and Dutch
clover. Where there are few cats, on the contrary, the mice
flourish, the bees are destroyed, and the plants cease to bear

430

NINETEENTH CENTURY. pt. ill.

seed and to multiply. And so you see that it actually de-
pends upon the number of cats in the neighbourhood how-
many of these flowers there are growing in our fields.

But now let us suppose for a moment that among the
field-mice there are some whose skin has a slightly peculiar
smell, so that the cats do not eat them when they can find
others. Clearly these mice would live longest and have most
offspring \ and of these again, those with strong-smelling skins
would live ; and so after a time a new race of mice would
arise which would be independent of the cats, and the bees
would have a poor chance of living, and consequently the
flowers of bearing seeds.

But this might in the end give rise to quite a new race
of plants, for it is believed that some moths would visit the
clovers, only as Mr. Darwin points out, they are not heavy
enough to weigh down the petals of the flowers so as to
creep inside them. But as no two flowers are ever exactly
alike, it is very likely that the petals of some blossoms will
droop a little more than in the others, and so if the bees
became scarce, these blossoms with drooping petals might
live on, because the moths could creep into them and carry
their pollen from flower to flower ; and thus a new race of
clover with drooping petals might spring up independent of
the cats, the mice, and the bees, and would become a new
species.

You must especially notice in this imaginary example
that it is only useful variations which can be passed on
from generation to generation. If the smell of the mice
(which would probably come from some peculiarity in the
pores of the skin) did not preserve them from the cats, the
strong- smelling mice would not live, and a peculiar race
would not arise ; in the same Avay, if the drooping leaves of

CH XL. NATURAL SELECTION, 431

the clover did not enable the moths to enter, those plants
would die out like the others. And this is one of the most
striking facts which Mr. Darwin has pointed out ; namely,
that no variation will continue and increase from generation
to generation unless it is useful to the plant or animal which
possesses it ; so that if this theory be true, every beautiful
colour which we admire in animals and plants, every minute
detail in their form and structure, is not only to be admired
for its beauty, but because it is an evidence of that won-
derful harmony of nature which keeps every part, however
insignificant, exactly fitted to do its work in the one great
scheme of creation.

Difficulties in Natural History explained by Natural
Selection. — And now, if we adopt Mr. Darwin's explanation,
you will see how St.-Hilaire and Cuvier could both be
right when the one said that all animals are formed on
one plan, and the other that each part of an animal is
exactly fitted to work harmoniously with the rest of its
body. For if animals have been gradually altered the one
from the other, it is natural they should all be made on
one plan ; as, for instance, if the ancestor of the bat, millions
of years ago, was also the ancestor of those animals out of
which the horse has come, then the bones of the bat's wing
may well be similar to those of the horse ; while, on the
other hand, if no variation can become fixed, and develope
into important parts or organs unless it is useful, it is clear
that all the parts of an animal must have been gradually
modified so as to fit each other and to work in the best pos-
sible way for its well-being. Again, it explains why the living
animals in a country should be of the same class, though
slightly different from those found fossil in the earth. For
if in Australia the ancestors were pouched animals, it must

432 NINETEENTH CENTURY. ft. hi.

take a very long time before their descendants could be any-
thing else, although they might begin to differ in many
points.

Lastly, it enables us to understand why we find the lower
forms of life in the oldest rocks, and why gradually, as
animals multiplied and the struggle for life became greater,
more and more complicated forms should arise, from the
improvement and inheritance of specially useful parts ; so
that the higher, animals have a greater number of different
parts to perform different actions, just as a civiHzed country
with a great number of skilled people in it, has men of
different trades and professions, one to brew and one to
bake, one to dig the ground, and to grow cotton and flax,
and another to weave them into garments.

This will give you a very small glimpse of some of the
difficulties which are explained by the theory of natural
selection. The subject is so difficult to understand tho-
roughly, that you must not expect to have more than a
slight notion of it, and must be content for the present with
knowing that our greatest living naturalists, who have made
a careful study of living and fossil animals and plants, all
believe it to be true.

And as this is so, it is extremely foolish to be prejudiced
against it, as some people are, by the idea that animals
formed in this way can be less God's creation than if they
were made in any other way. The whole history of science
teaches us that men, in all ages, have constantly taken false
alarm when it has been shown that God's ways are not our
ways, and that the universe is governed by far wider and
more constant laws than we had imagined in our little
minds. But in the same way as the planets are none the
less held in God's hand because we now know that it is by

CH. XL. CONCLUDING REMARKS. 433

the law of gravitation that He governs their movements, so
every plant and animal must be equally His creation, in
whatever way they have been developed. Above and be-
yond all these laws which we can trace, there remains ever
the One Great and Supreme Creator whom Anaxagoras wor-
shipped instead of the heathen gods of Greece (see p. 14),
when his fellow-countrymen condemned him as an unbe-
liever because he believed not in many, but in One God.

A humble, earnest spirit seeking knowledge must indeed
find in modern science a deep revelation of the Unity and
Unchangeableness of the Creator. Instead of many widely
different sciences standing each alone, which the great men
of earlier centuries worked out, we are beginning to be able
to discern one constant power working through them all ;
while still new fields of discovery, such as that which
spectrum analysis has only lately opened out to us, help us to
bear in mind how little we know, and how much more vast
than anything that we can imagine, must be the great scheme
of Creation which is being worked out around and within us.

Concluding Remarks. — We have now arrived at the end
of our history, for a summary of the science of the nineteenth
century is manifestly impossible. The subject has become
too vast to be dealt with in a short sketch, even if the limits
of this little volume were not already reached. Besides, as
we have not mentioned the work of living men, except in
cases such as those of Kirchhoff and Darwin, where it was
impossible to be avoided, we have not really examined the
science of this century, but only very small portions of it.
• We can therefore, in conclusion, only try to understand the
tendency of the science of our day as compared with that of
earlier centuries.

20

434

NINETEENTH CENTURY. pt. hi.

The work of the sixteenth century, as we saw (p. 82),
was to overcome that blind worship of authority which had
sprung up during the Dark Ages, and which is the greatest
enemy to true knowledge.

In the seventeenth century the march of scientific
discovery began with Galileo, and advanced slowly but
triumphantly through many dangers and difficulties, till
it ended in the grand generalizations of Newton. This
was the first great era of modern science, especially of
astronomy and physics, though biology also made a great
stride when Harvey demonstrated the circulation of the
blood.

The eighteenth century continued the same work of
patient enquiry, completing the harmony of astronomy by
bringing the observed movements of the planets under
Newton's law of gravitation ; founding chemistry upon a
firm basis of careful experiment ; creating the sciences of
zoology and botany, by establishing true systems of classi-
fication ; discovering the hitherto almost unknown force of
electricity j and reading in the crust of the earth the history
of the past ages of our planet.

And so when the nineteenth century opened, men found
themselves with an immense mass of known facts and-
careful experiments, which had been accumulated during
the last two centuries, and which were very difficult to deal
with, because it had become almost impossible for any single
mind to grasp them all. The scientific men of our century
have therefore become divided into two great classes. On the
one hand men have devoted themselves to special sciences,
and even to special branches of a science, so that a man will
often spend his whole life in the study of one department of
chemistry or physics, or in investigating one little group of

CH. XL. CONCLUDING REMARKS. 435

insects j and in this way discoveries of great value have
been made.

On the other hand great minds among us have taken up
the separate facts collected by specialists, and have woven
the whole of physical science into one grand scheme. Such
men as Faraday, Helmholtz, Sir W. Thomson, and Grove,
together with many others, have done their part in this work,
so that now all the various physical forces have been shown
to be probably phases of one great force, appearing under
many forms. For the future no one physical force can be
studied as if it existed by itself alone, for each is shown to
arise out of and to pass into others. Heat, electricity, mag-
netism, chemical affinity, motion — all are related to each
other, and we cannot call any one of them the ruler over the
rest. Like the colours on the soap-bubble, they each take
their turn in appearing and disappearing, according to the
conditions under which they arise. Their relations are
almost infinitely complex, and we have still much to learn
about them ; but the grand fact that they pass the one into
the other without loss of energy has been demonstrated in
our century ; and, under the names of ' the conservation of
energy,' and ' the correlation of the physical forces/ is one
of the greatest results of modem science.

The same tendency may be seen in the study of those
sciences which relate to life. Here again modern investiga-
tion links together the scattered observations of ages, and
unites them all in the theory of ' evolution,' or the gradual
unfolding of nature ; a theory which has been worked out
in all its details by Herbert Spencer, one of our greatest
living thinkers. In astronomy, indeed, we already catch
a glimpse of this law in the probable formation of the
heavenly bodies out of gaseous star-matter ; and in the or-

436 NINETEENTH CENTURY. pt. hi.

ganic world we find it even more firmly held by scientific
men in the belief that all the many forms of plant and
animal life have been unfolded out of a few simple forms,
just as the stem, the leaf, and the flower aire evolved out of
a simple seed.

Whether this theory is true or not, it must be the work
of many generations to prove, for the history of science
teaches us that nothing but truth can stand the test of long
investigation, while no power or authority can resist in the
end that which is true. The mistaken theory of phlogiston
did its work in gathering together many scattered facts in
chemistry, and then died a natural death when the discovery
of oxygen threw more light upon the subject ; while no
authority or persecution could suppress the true theory that
the earth moves round the sun.

It is of great importance that we should all learn this
lesson, to have faith in the invincible power of truth j for it
would almost seem as if all the experience of past centuries
had hardly yet convinced us. We still, like the Aristotelians
and the judges of the Inquisition, often make hasty and
ignorant assertions, and try rather to prop up by authority
that which we believe, than to enquire earnestly whether it
is true. Yet every page in the History of Science teaches
the contrary lesson. So much as is true in any belief will
stand because it is true; while that which is mistaken will
fade away before earnest and impartial examination. Our
part is to endeavour, like the great men of whom we have
been reading, to open our eyes to the laws which surround
us, and which are only hidden from us by our ignorance.
And from whatever source we derive our knowledge we
must remember that it is very little after all, and be ready at
all times to exanmze new facts, even though they may seem

CH. XL. CONCLUDING REMARKS. 437

to upset some of our favourite opinions; for unless we
know everything, it is certain that we must at times find
that we have been mistaken.

Those who will labour in this spirit of seeking the truth
for itself will find their reward in the ever-increasing delight
they will feel in studying God's works, and in the assurance
which they will meet with at every step, that nothing can
happen except under the guidance of His laws. True
science, like true religion, leads to an entire and childlike
dependence upon the Invisible Ruler of the universe. It
makes us eager to study God's laws, that we may live in
accordance with them, and diminish some of the gross
ignorance which now prevails ; while at the same time it
leads even the most instructed to feel how extremely limited
our knowledge is, and that we are after all like inexperienced
children, dependent upon the love and power of our Maker
to bring us safely out of darkness into light.

Chief Works consulted, — Darwin's ' Origin of Species ; ' Wallace's
'Natural Selection;' Huxley's 'Lectures to "Working Men;' Lyell's
'Principles of Geology.'

CHRONOLOGICAL TABLES

OF THE

RISE AND PROGRESS OF THE VARIOUS
I BRANCHES OF SCIENCE

440

CHRONOLOGICAL TABLE.

SCIENCE OF THE GREEKS.

FROM B.C. 639 TO A.D. 2CX).

TJte dates of this table refer to the years in ivhich each particular step in advatice was
made; but iip to the end of the Middle Ages they nitist be regarded as merely
approximative.

Astronomy.

B.C.

600. Thales marks
out solstices and
equinoxes, p. 8.

570. Anaximan-
der — The sun-
dial ; the phases
of the moon, p. 9.

i50o. Pythagoras

— The earth
moves ; morn-
ing and even-
ing star the
same, p. 11.

450. Anaxagoras

— Nature of
sun and moon ;
eclipses ; move-
ments of the
planets, p. 13.

400. Democrituson
Milky Way, p. 15.

360. Eudoxus on
movements of
the planets, p.

357. Aristotle on
occultation of
Mars ; asserts
that the earth is
round, p. 16.
Ecliptic and Zo-
diac understood
by the Greeks,
p. 18.

Aristarchus.
Earth moves
round the sun ;
obliquity of
ecliptic; rota-
tion of earth
on its axis, p. 20.

130. Hipparchus
on precession of
the equinoxes ;
calculates ec-
lipses, p. 29.

A. D. 100. Ptole-
my founds the
Ptolemaic sys-
tem, p. 32.

Physics and
Mechanics.

260. Euclid on
light travelling
in straight lines,
p. 21.

250. Archimedes
on the lever ;
Hiero's crown
and specific gra-
vity ; screw of
Archimedes, pp.
22-25.

120. Hero's en-
gine, p. 245.

Chemistry.

Greeks knew how
to extract iron,
mercury, and
other metals
from the ore ;
and make co-
lours out of
earths, p. 40.

Physical

Geography and

Geology.

570. Anaximan-
der makes a
map of the
known world, p.
10.

500. Pythagoras
on changes of
land and sea ;
on earthquakes,
voicanos, and
p e t r i f yi ng
springs, pp. 11-

230. Eratosthe-
nes lays down
first parallel of
latitude ; mea-
sures circumfer-
ence of the
earth ; studies
mountai n
chains, pp. 27-
29.

A.D. 100. Ptole-
my on geo-
graphy, p. 23.

Strabo on earth-
quakes and vol-
canoes, p. 33.

Biology.

390. Hippocrates
father of medi-
cine ; separates
medicine from
the priesthood,

p. 15.

341. Aristotle
founder of zoo-
logy ; studies
the nature of
plants and ani-
mals, p. 16.

340. Theophras-
tus first bota-
nist, p. 17.

Erasistratus and
Herophilus the
first anato-
mists ; they
study brain,
muscles, and
nerves, p. 26.

A.D. 160. Galen,
physician,
studies nerves
and arteries ;
works out a
theory of medi-
cine, p. 33.

CHRONOLOGICAL TABLE.

441

SCIENCE OF THE MIDDLE OR DARK AGES.

FROM A.D. 700 TO 1500.

The Arabs great
astronomers, but
mix up astrono-
my with astro-
logy, p. 45-

Astronomy.

goo. Albategnius
calculates the
length of the
year, p. 45.

1008. Ebn Junis
draws up astro-
nomical tables,
p. 46.

Physics and
Mechanics.

(900. Ben Mtisa
on algebra and
nutnerals).

(1000. Gerhertht-
trodtices A rabic
ntimerals into
Euro;pe\

1030. Alhazen on
refraction of
light ; on atmo-
spheric reflec-
tion ; on mag-
nifying glasses,
pp. 46-50.

1 240. Roger Ba-
con and Vitellio
on cause of the
rainbow, p. 53.

1302. Flavio Gio-
ja invents the
mariner's com-
pass, p. 53. _

1438. Invention
of printing, p.

55-
1480. Leonardo
da Vinci makes
water-mills and
river-locks, p.
58.

Chemistry.

800. Marcus
Grsecus makes
gunpowder, p.
42.

Arabian alche-
mists ; gases
called 'spirit,'
p. 41.

)o. Geber the
founder of che-
mistry ; distilla-
tion and sub-
limation ; makes
nitric and sul-
phuric acid ;
discovers t hat
heating a metal
adds to its
weight, pp. 43-
45-

1240. Roger
Bacon's experi-
ments on air ;
he makes gun-
powder; his
' Opus Majus.'
p. 52.

Physical

Geography and

Geology.

80. Avicenna, a
famous writer
on minerals, p.
50.

1492. Columbus
discovers Ame-
rica, p. 36.

1497. Vasco di
Gama sails
round the Cape
of Good Hope ;
sees the south-
em stars, p. 57.

Biology .

Arabs learn medi-
cal science from
Jews and Nes-
torians, p. 40.

700 to 800. Medi-
cal schools of
Bagdad and Sa-
lerno flourish,
p. 40.

Arabs devote
themselves to
medicine be-
cause dissection
is forbidden by
the Koran, p.
40.

920. Medical
school of Cor-
dova founded,
p. 40.

1030. Alhazen on
nature of sight ;
why we do not
see double with
two ej'-es, pp.
47-49-

442

CHRONOLOGICAL TABLE.

RISE OF MODERN SCIENCE.

FROM A.D. 1 5 19 TO 1604.

Astronomy.

Physics and
Mechanics.

Chemistry.

Physical

Geography and

Geology.

Biology.

1519. Magellan's

1530. Paracelsus,

ship sails round

chemist and al-

the world, p. 67.

1542. Vesalius

1543. Copemican

chemist, sepa-

refutes Galen ;

system publish-

rates out gold

his anatomical

ed, p. 65.

1560. Baptiste
Porta invents
the camera ob*
scura, p. 74.

by means of
aquafortis, p.
72.

1565. Gesner on

drawings, p. 66.

1548. Fallopius
on anatomy, p.
68.

1551. Gesner,
first _ zoological
cabinet and
botanical g a r-
den, p. 68.

1560. Eustachi-
us. — Eustach-
ian tube, p. 68.

1560. Porta on
structure of the
eye, p. 76,

1565. Gesner 's

157 5- Tycho

mineralogy and

'History of

Brahe's obser-

fossil shells, p.

Animals,' p. 69 ;

vatory on Huen

70.

his classifica-

island; Tycho-

tion of plants.

nic system, p.
78.
1576. Tycho in

p. 70.

Bohemia, p. 79.

1580. Porta's
engine, p. 246.

1580. Palissy,
the potter, in-

1583. Galileo on

sists that fossil

1583. Caesal-

the pendulum.

shells were once

pinus classifies

P- 79- ^ .

real shells, p.

plants by their

1589. On falhng

215.

flowers and

bodies, p. 80,

seeds, p. 71.

1592. On motion

of heavy bodies.

-

p. 82.

1592. Stevinus

1594. Kepler be-

on statics, p. 82.

gins to study the

planets, p. p5.

1597. He joins

Tycho in Bo-

hemia, p. 9S._

1599. Rudolphine

tables begun, p.

79-
1600. Bruno

1600. Kircher in-

1603. Fabriclus

burnt at the

vents the magic

discovers valves

Stake, p. 83.

lantern, p. 76.
1600. Gilbert
makes experi-
ments on e 1 e c-

in veins, p. 110.

1604. Kepler on

formation of

images on the

tricity, p. 77.

retina, p. 96.

CHRONOLOGICAL TABLE.

443

PROGRESS OF MODERN SCIENCE.

FROM A.D 1609 TO 1 642.

Astronomy.

1609. Galileo
discovers secon-
dary light of the

. moon ; Jupiter's
moons ; phases
of Venus, pp.
89-92.

1609. Kepler's
two first laws,
pp. 97-99.

161 1. Galileo ob-
serves sun-spots
and proves ro-
tation of sun on
its axis, p. 92.

i6i8. Kepler's
third law, p.
100.

Physics and
Mechanics.

1628. Kepler com-
pletes Rudol-
phine tables;
and foretells
transits of Venus
and Mercury,

P- 157-
I 6 3 1. Gassendi
observes transit
of Mercury, p.

157-

1632. Galileo s
system of the
world ; his re-
cantation, p. 93.

1639. Horrocks
observes transit
of Venus, p.

157-
1642. Death of
Galileo and
birth of New-
ton, pp. 64-147.

1609. Invention
of the telescope,
p. 87 ; Galileo's
telescope, p. 89.

1611. Kepler's
telescope, p. 97.

1615. Solomon
Caus' engine,
p. 246.

1620. Drebbel,
alcohol thermo-
meter, p. 120.

620. Bacon's
'Novum O r-
ganum,' p. 103 ;
Bacon suggests
that heat may
be a movement,

P- 330- , , .

1621. Snellius
discovers law
of refraction, p.
106.

X625. De Domi-
nis explains the
rainbow, p. 164.

1637. Descartes
on light and re-
fraction, pp.

107-165.

Chemistry.

1624. Van Hel-
mont introduces
the term gas, p.
72.

Physical

Geography and

Geology.

Biology.

1619. Harvey
discovers circu-
lation of the
blood, pp. iio-
114.

622. Asellius
discovers lac-
teals, 114.

444

CHRONOLOGICAL TABLE.

PROGRESS OF MODERN SCIENCE.

FROM A.D. 1644 TO 1670.

Astronomy.

Physics and
Mechanics.

Chemistry.

Physical

Geography and

Geology.

Biology.

1644. Torricelli

invents the ba-

(1645. First

rometer, p. 116.

7nee tings of

,

1646. Pascal

Royal Society,

proves the

p. 124.)

1647. Pecquet

weight of air.

on the thoracic

p. 119.

duct, p. 114.
1649 Riidbeck

1650. Guericke

discovers lym-

invents the air-

phatics, p. 115.

pump : Magde-

1656. Malpighi

burg hemi-

professor of me-

spheres : first

dicine at Bo-

electrical m a -

logna, p. 138.

chine, p. 121-

123.

1658. Huyghens

1659. Huyghens

on cycloidal

discovers Sa-

pendulums, p.

turn's ring, and

174.

one satellite, p.

I 661. Poyle's

1661. Malpighi

174,

law of compres-

(1662. Acadetnie

uses microscope

sion of gases, p.

des Sciences

to examine air-

128.

founded, p.
126.)

cells of the
lungs ; discovers

1666. Newton

M alpighian

on method of

layer ; studies

fluxions; first

anatomy of in-

idea of gravita-

sects, pp. 137-

tion, pp, '•41-

139-

150.

1663. Marquis
of Worcester's
engine, p. 246.

1666-1671. New-
ton on disper-
sion of light,
proves its' com-
pound nature,
pp. 166-169.

1665. Hooke on
use of air in
combustion, p.
130.

1665. Boyle's ex-
periments on
air, p. 130.

1669. Steno on
fossils and petri-
factions, p. 215.

1663-1666. Jour-
neys of Ray and
Willughby, p.
143-

1670. First mer-

1670. M a y 0 w

1670. Scilla on

1670. M a y 0 w

curial thermo-

discovers ' fire-

fossils of Cala-

on respiration,

meter, p. 120.

air,' and shows
it is used in
burning, p. 131.
1670. Beecher
proposes theory
of 'phlogiston,'
P- 1C35-

bria, p. 216,

P- 134.

i

CHRONOLOGICAL TABLE.

445

PROGRESS OF MODERN SCIENCE.

FROM A.D. 1674 TO 1 732.

Astronomy.

1676. Halley ob-
serves transit of
Mercury, p.
158.

1682. Newton
works out and
publishes the
law of gravita-
tion, pp. 150-

155-

1682. Halley
foretells the re-
turn of a comet,
p. 162.

1687. Newton's
' P r in c i p i a '
p u b 1 i s h e d, p.
153-

691. Halley's
method of mea-
suring the sun's
distance by the
transit of Venus,
p. 158.

Physics and
Mechanics.

1676. Roemer
measures velo-
city of light, p.
172.

1678. Huyghens
proposes undu-
latory theory of
light; law of
double refrac-
tion, p, 175-179'

1690. Papln's
heat-engine, p.
246.

r722. Graham on
shifting of mag-
netic needle, p.

355- ^ „
1727. Bradley on

nutation and

aberration, p.

265.

Chemistry.

Physical

Geography and

Geology.

Biology^

1682. Picart
measures the
size of the earth,
p. 150.

598. Savery s
heat-engine, p.
246.
1705. Newco-
men's engine,
p. 246.

1729. C. More
Hall on disper-
sion of light in
flint and crown
glass, p. 169.

1732. Du Faye
on electricity,
p. 254.

1701. Boerhaave
founder of or-
ganic chemis-
try, pp. 190-194.

1718. Hales' ex-
periments on
gases, p. 226.

1729. S t a h 1
founds a system
of chemistry on
the theory of
phlogiston, p.
135.

1695. Woodward,
on fossils and
succession of
formations in
England, p.
216.

1674. Malpighi
on structure of
plants, p. 140.

1677. Leeuwen-
hoeck discovers
animalcules, p.
139-

1682, Grew on
structure of
plants, p. 140.

1690. Rivi nus
proposes to give
two names t o
each plant, p.
209.

1693. Ray and
Willughby's
classification of
animals ; Ray's
system of plants,
pp. 142-146.

1694. Tourne-
fort's system of
plants, p. 145.

1707. Buffonand
Linnseus bom,
p. 204.

1727. Hales on
respiration of
plants and for-
mation of sap,
P- 193-

446

CHRONOLOGICAL TABLE.

PROGRESS OF MODERN SCIENCE.

FROM A.D. 1738 TO 1 766.

Astronomy.

Physics and
Mechanics.

Chemistry.

Physical

Geography and

Geology.

Biology.

1738. Bougier

makes the first

1740. Hawksbee's

1740. Lazzaro

attempt to mea-

electrical ma-

Moro _ on the

1741. Linnaeus'

sure the earth's

chine, p. 123.

formation of the

botanical gar-

density, p. 278.

1744. Celsius,
Fahrenheit, and
Reaumur mark

crust of the
earth, p. 216.

den at Upsala,
p. 208.
1743. Haller on
contraction of
the muscles ;
anatomical

off degrees on

plates, pp. 195-

thermometer, p.

.197.

120.

.

1746. Franklin's

»

1

experiments in

1748. Haller and

electricity, p.

Hunter on com-

254-

parative ana-

tomy, p. 197.

1749. Hutton be-

1749. Buffon's

gins to examine

' Natural His-

the formations

tory ; ' distribu-

of the earth's

tion of animals.

crust, p. 219.

p. 205.
1750. Dauben-
ton's anatomy.

1752. Franklin

p. 205.

proves identity

1753. Linnseus

of electricity

introduces spe-

and lightning.

cific names, p.

p. 256.

1756. Black ex-

208.
1754. Bonnet on
leaves of plants,

1757. Dollond's

tracts * fixed

p. 200.

achromatic tele-

air' from lime-

scope, p. 169.

stone and ex-

1760. Black on

amines it, p. 226.

1 761. Sun's dis-

latent heat in

1761. Bergmann

tance first mea-

melting ice and

on chemical af-

1762. Bonnet and

sured by the

in steam, p. 241.

finity & ' tests : '

Spallanzani on

transit of Ve-

proves that

regrowth of se-

nus ; Delisle's

fixed air is an

vered limbs, p.

method intro-

acid, p. 228.

201.

duced, pp. 162

and 266.

1764. Bonnet on

1 764- 1 780. La-

development of

grange, libra-

1765. Watt's

animals, p. 202.

tionofthemoon.

steam - engine.

1766. Cavendish

p. 267.

pp. 244-249.

discovers hy-

drogen, p. 230.

CHRONOLOGICAL TABLE.

447

PROGRESS OF MODERN SCIENCE.

FROM A.D. 1769 TO 1 7 89.

Astronomy.

1774. Maskelyne
measures the
earth's density
by Schehallien
experiment, p.
277.

1774-1783. La-
place on long
inequality o f
Jupiter and Sa-
turn ; moon's
acceleration, p.
269.

1776. Lagrange
proves the sta-
bility of the
planetary or-
bits, p. 270.

1781. Uranus
discovered by
Herschel, p. 272.

1783. Proves the
rotation of bi-
nary stars, p.
273-

1786. He dis-
covers star-clus-
ters and nebu-
lae, p. 274 ; and
the motion of
the solar sys-
tem towards
Hercules, p.
275-

Physics and
Mechanics.

1769. Boulton
and Watt part-
ners, p. 251.

1785. Watt's
double - acting
steam - engine,
p. 251.

1789. Electricity
experiments of
Galvani ; con-
troversy between
Volta and Gal-
vani, pp. 259-
261.

Chemistry.

1772. Rutherford
describes nitro-
gen, p. 23s.

1774. Priestley
discovers oxy-
gen, p. 231.

1775. Scheele dis-
covers oxygen,
p. 231.

1778. Lavoisier
overthrows the
theory of 'phlo-
giston ' by prov-
ing the action
of oxygen, p.

235-

1779. Shows the
composition of
carbonic acid,
p. 238.

1784. Cavendish
explodes oxy-
gen and hydro-
gen, forming
water, p. 231.

1787. Lavoisier
founds a new
chemical no-
menclature, p.

239.
1789. Lavoisier's
* Elements of
Chemistry' pub-
lished, p. 239.

Physical

Geography and

Geology.

1769. Cook's
voyage to the
South Seas for
the second tran-
sit measure-
ment, p. 162.

1775. Werner lec-
tures on geo-
logy at Frey-
berg, p. 217.

1784. Disputes
between Nep-
tunists and Vul-
canists, p. 218.

1785. Sir James
Hall on melted
rock ; Hutton
on granite veins,
p. 221.

1788. Button's
' Theory of the
Earth' publish-
ed, p. 219.

Biology.

1768. Foundation
of the Linnaean
system ; * Sys-
tema Naturae '
completed, pp.
210-211.

1772, Priestley on
breathing of
plants, p. 232.

1778. Death of
Linnaeus ; his
collections
brought to Eng-
land, p. 212.

1783. Hunter's
museum begun
in Leicester
Square, p. 199.

1789. Animal elec-
tricity disco-
vered by Gal-
vani, p. 259.

1789. Jussleu

founds the Na-
tural System of
plants, p. 382.

448

CHRONOLOGICAL TABLE.

PROGRESS OF MODERN SCIENCE.

FROM A.D. 1790 TO 181I.

Astronomy.

1793. Herschel
on cause of sun-
spots, p. 353.

1799. Laplace's
'Mecaniqu e
Celeste,' p. 271.

:8oi. Piazzi dis-
covers Ceres,
the first of the
asteroids, p. 289.

1802-4-7. Dis-
covery of other
asteroids. Ol-
bers suggests
they are frag-
ments of a
planet, p. 290.

1803. Biot on me-
teoric stones, p.
297.

Physics and
Mechanics.

1792. Voltaic or
chemical elec-
tricity, p. 261.

1798. Rumford
boils water by
friction, p. 330.

1799. Davy melts
ice by friction,

P- 333-

1800. Voltaic
pile, p. 263.

1800. Sir W. Her-
schel discovers
dark heat-rays,
P- 315-

1801. Ritter dis-
covers chemical
rays, p. 316.

1 801. Young on
interference of
light, p. 302.

1802. Wedgwood
and Davy, sun-
pictures, p. 317.

1802. Wollaston
lines of spec-
trum, p. 318.

1804. Fraunhofer
compares lines
in the spectrum
of sun and stars,
p. 319-

1808. Malus dis-
covers polarisa-
tion of light by
reflection, p.
309-

181 1. Leslie and
Melloni on heat
rays, p. 340.

Chemistry.

1794. Lavoisier
guillotined, p.
240.

1800. Nicholson
and Carlisle, de-
composition of
water, p. 364.

1800. Davy on
laughing gas,
P- 363-

1806. Davy on
electrolysis ;
discovers potas-
sium and so-
dium, p. 364.

1807. Davy on
hydrochloric
acid, p. 365.

1808. Dal ton,
law of multiple
proper tions ;
atomic theory,

PP- 371-374-
1808. Gay-Lus-
sac on combina-
tion in multiple
volumes, p. 377.

Physical

Geography and

Geology.

1790. Wm. Smith
studies the suc-
cession of strata,
p. 222.

1790. De Saus-
sure studies the
action of gla-
ciers, p. 412.

1799. Humboldt's
journeys in
America. He
traces isother-
mal lines, p.
385.

Biology.

1790. Goethe on
the metamor-
phosis of plants,
p. 381.

1800. Cuvier's
lectures on ana-
tomy ; he in-
sists on the fit-
ness of organisa-
tion in indi-
vidual animals,

P- 395-

1 801. Lamarck
on development
of animals, p.
391-

1802. G. St.-Hi-
laire brings zoo-
logical collec-
tions from

Egypt, p- 391-

804. Humboldt
on distribution
o( p'ants, p. 385.

CHRONOLOGICAL TABLE.

449

RISE OF MODERN SCIENCE.

FROM A.D. l8l2 TO 1 848.

Astronomy.

Physics and
Mechanics.

Chemistry.

Physical

Geography and

Geology.

Biology.

1812. Former

1812. Cuvier re-

periods of life

stores the fossil

on the globe

animals of Paris,

proved by

p. 397-

Cuvier, p. 397.

1815. Davy's

1815. W. Smith's

safety-lamp, p.

geological map.

363.

p. 224.

1 816. Fresnel

and Young, po-

1817. Buckland's

1817. Cuvier 's

larization of

geological lec-

'Animal King-

light, p. 311.

1818. Berzellius

tures, p. 405.

dom ' published,
p. 396.
1818. G. St.-Hi-

1819. Encke's

1819. Oersted,

on use of the

laire on unity of

comet, p. 2qo.

electro-magnet-

blow - pipe, p.

plan in animals.

ism, p. 342.

370.

P- 393-

1S20-1838. SirJ.

1820. Ampere,

Herschel studies

electro-magnet-

stars of the

ism, p. 345.

southern hemi-

1821. Faraday,

sphere ; Magel-

electro-magnet-

lanic clouds, p.

ism, p. 349.

295-

1822. Seebeck on
thermo - electri-

1822. Herschel
on use of spec-

city, p. 352.

troscope to de-

1825. McEnery

1826-60. Schwabe

1826. Mo bill

tect chemical

discovers flint

proves periodi-

proves the

elements, p. 321.

tools, with bones

1828. Von Baer's

city of sun-

truth of animal

of extinct ani-

law of embryo-

spots, p. 353.

electricity, p.

mals in Kent's

logical develop-

1826. Biela's

261.

Cavern, p. 416.

ment, p. 400. 1

comet, p. 2gi.

1830. Liebig's
analyses of or-
g a n i c s u b-
stances, p. 377,

1830. Lyell's' Geo-
logy ; ' he in-
sists on suffi-
ciency of causes

1
1

1832. Discovery

like the present

1832. Death of

s

of chloroform

to explain the

Cuvier, p. 400.

and chlorale by

past history of

Liebig, p. 378.

the globe, p.

1834. Faraday on

405-

1837. WheatsLone

electrolysis;

1838. Herschel's

and Cooke, elec-

chemical nature

1840. Agassiz on

' Outlines of As-

tric telegraph.

of electric cur-

glacial period

1839. Agassiz

tronomy ' pub-

P- 356.

rent; invention

and blocks car-

on freshwater

lished, p. 2q6.

1839-42. Seguin

of voltameter.

ried over Eu-

fishes, p. 410.

and Mayer on

P- 367-

rope by ice, p.

1840-48. Organic

relation between

411.

chemistry, p.

heat and work.

377.

P- 335-

1839. Daguerreo-

types, p. 317.

450

CFIRONOLOGICAL TABLE,

RISE OF MODERN SCIENCE.

FROM A.D. 1843 TO 1 874.

Astronomy.

1845. Division of
Biela's comet,
p. 290.

1845-6. Adams
and Leverrier
work out the
position of Nep-
tune ; Galle finds
the planet, p.
290.

850. Lamont,
periodicity of
magnetic dis-
turbance, p. 355.

859. Carrlngton
and Hodgson,
sun - spot and
magnetic dis-
turbance, p. 355.

1862-66. Schiape-
relli, Adams,
and Leverrier,
discover the or-
bits of comets
and meteor sys-
tems, p. 298.

1874. Expeditions
to observe the
transit of Venus,
p. 162.

Physics and
Mechanics.

1843-49. Joule
on equivalent
of heat ; dyna-
mical theory of
heat, p. 335.
- Hirn's experi-
ments on heat,
P- 338.

: 860-1 866. Four
nev/ metals dis-
covered by spec-
trum analysis,
P- 323-

1861. Bunsenand
Kirchhoff dis-
cover the mean-
ing of the lines
in the spectrum,

P- 323-

1862. Huggms
and Miller,
spectrum analy-
sis of the stars
and nebulae, p.
326.

— Alexander
Herschel, spec-
trum of falling
stars, p. 328.

Chemistry.

548. Wohler
makes organic
elements artifi-
cially, p. 397.
56i. Metals in
the atmosphere
of the sun and
stars discovered
by spectrum
analysis, p. 326.
1862. Gas^ of
the nebulae dis-
covered by spec-
trum analysis,
P- 327-

Physical

Geography and

Geology.

1847. Boucher de
Perthes dis-
covers flint im-
plements at
Abbeville, p.
415-

1853. Discovery
of Swiss lake-
dwellings, p.
416.

1858. Humboldt's
* Cosmos ' pub-
lished ; death of
Humboldt, p.
386.

1863. ^ Lyell's
• Antiquity of
Man,' p. 418.

Biology.

1858. Theory of;
natural selec-
tion by Darwin
and Wallace,
p. 426.

1859. Darwin s
' Origin of Spe-
cies,' p. 425.

1852-1872. Dis-
covery of inter-
mediate fossil
forms, p. 424.

bO

Hippocrates ; Aristotle ;
Theophrastus ; Erasis-
tratus ; Herophilus ;
Galen.

1
1

1
i

Vesalius ; Fallopius ; Eu-
stachius ; Gesner ; Cai-
salpinus ; Fabrlcius.

Harvey; Asellius ; Riid-
beck ; Malpighi : Leeu-
wenhoeck ; Grew ; Ray ;
Willughby ; Toumefort.

Boerhaave; Hales; Hal-
ler ; Hunter ; Bonnet ;
Spallanzani ; Buffon ;
Daubenton ; Linnsus :
Jussieu.

Lamarck ; Goethe ; G. St.-
Hilaire ; Cuvier ; Von
Baer ; Boucher de
Perthes ; Darwin ; Wal-
lace ; Agassiz.

-a

3

§* •

Wo
'!n

Anaximander.

Pythagoras.

Eratosthenes.

Ptolemy.

Strabo.

Avicenna.
Columbus.
Vasco di Gama.
Magellan.

Ofin

Steno.
Scilla.
Woodward.

Lazzaro Moro.
Werner.
Hutton.
William Smith.
De Saussure.

Humboldt.

Buckland.

Lyell._

Agassiz.

Murchiscn.

1/1

's

o

Marcus Grsecus.
Geber.
Roger Bacon.

a

Mayow.
Beecher.
Stahl.

Boerhaave ; Hales ;
Black ; Bergmann ;
Cavendish ; Priestley ;
Scheele ; Rutherford ;
Lavoisier.

Wollaston ; Berzelius ;
Biot ; Dalton ; Thom-
son ; Gay-Lussac ;
Davy ; Faraday ; Lie
big ; Wohler ; Bunsen ;
Miller.

o

V

H-5

Gerbert ; Ben Musa ;
Alhazen ; Roger Bacon ;
Vitellio ; Flavio Gioja ;
Leonardo da Vinci.

(U

Snellius ; Descartes ;
Bacon ; Drebbel ; Tor-
ricelli ; Guericke ;
Boyle ; Hooke ; Huy-
ghens ; Roemer.

Du Faye ; Celsius ;
Fahrenheit ; Reaumur ;
Watt ; Franklin ; Gal-
vani ; Volta ; Rumford.

Young ; Malus ; Fresnel ;
Arago ; Oersted ; Am-
pere ; Seebeck ; Brew-
ster ; Sabine ; Fraun-
hofer ; Kirchhoff ; Hug-
gins ; Mayer ; Joule ;
Wheatstone.

6
o

a

e

Thales, Anaximander;
Pythagoras ; Anaxa-
goras ; Democritus ;
Eudoxus ; Aristotle ;
Aristarchus ; Hippar-
chus ; Ptolemy.

u5

■3.2

Copernicus.
Tycho Brahe.
Giordano Bruno.

Galileo ; Kepler ; Gas-
sendi ; Horrocks ;
Newton ; Huyghens ;
Halley.

Bradley ; Delisle ;
Lagrange ; Laplace ;
Herschel ; Maskelyne.

Piazzi ; Olbers ; Encke ;
Gauss ; Sir J. Herschel ;
Airy ; Adams ; Lever-
rier ; Galle ; Schwabe ;
Sohiaparelli.

1

Middle
Ages.

Sixtheenth
Century.

lb
a 3

4)0

S 3

« 2
■S c

p

INDEX.

ABBEVILLE

ABBEVILLE flint implements, 415
Aberration of fixed stars, 265
Academies of science founded, 124
' Academy of Secrets ' at Naples, 74
Achromatic telescopes, 169
Acids, strong, discovered by Geber, 45
Adams calculates the position of Neptune,

292 ; on November meteors, 299
^sculapius god of medicine, 15
Aerial acid, Bergmann on, 230
Agassiz, his history, 410 ; on glacial period,

411-15 ; his natural history school, 411 ;

recognises glaciation in Scotland, 414
Aigle, meteoric stone-fall at, 297
Air, Boyle and Hooka, experiment on,

130 ; Mayow on, 131 ; -cells studied by

Malpighi, 138 ; -pUmp, section of, 121 ;

Guericke's, 121 ; -tubes of insects, 139
Airy, Adam's paper on Neptune sent to, 293
Albategnius calculates length of year, 45
Albinus, anatomical drawings of, 196
Alchemists, Arabian, 41
Aldebaran, spectrum of, 327
Alembert, d', brings Laplace to Paris, 267
Alexandria, founding of the city of, 18 ;

school of learning at, 18 ; taken by the

Arabs, 39 ; Egyptian animals preserved

at, 391
Algebra, an Arabian name, 46
Alhazen on eyesight, 47 ; on refraction,

47 ; on atmospheric refraction, 48 ; on

magnifying power of lenses, 49
Alps, glaciers of the, 412
Amazons, closely related butterflies of the,

420
Amber, electric nature of, 77
America, Agassiz natural history school in,

411 ; glaciation of, 414
Ammonia, origin of name, 45
Ampere, early life of, 343 ; on direction of

magnetic current, 345 ; on electro-mag-

ANIMALS

nets, 347 ; invents the galvanometer, 351 ;
on cause of terrestrial magnetism, 352 ;
suggests electric telegraph, 357

Analysis term explained, 371 ; of sub-
stances by tests, 229 ; of organic sub-
stances, 192, 377 ; different methods of,
369 ; Spectrum-, 315

Anatomy, Erasistratus and Herophilus on,
26 ; Vesalius on, 67 ; Eustachius and
Fallopius on, 68 ; vegetable-, 140 ; rise of
comparative, 197 ; Haller and Hunter
on, 199 ; Cuvier on, 395

Anatomical plates of Vesalius, 67 ; of Haller,
196

Anaxagoras on the moon and on eclipses,
13 ; banished, 14

Anaximander, science of, 9

Anderson brings Newcomen engine to Watt,

245

Anderson, Mr., gave Penikese island, 411

Animal, substances made of altered vege-
table matter, 194 ; electricity, 259, 261

Animalcules, discovery of, 140

Animals, Cuvier on internal structure of,
396 ; fossil, restored by Cuvier, 397 ;
Lamarck on development of, 393 ; simi-
larity of structure in, 394 ; difficulty in
distinguishing species of, 420 ; useless
organs in, 421 alike in the embryo, 421 ;
living and fossil nearly related, 422 ;
gradual succession of, on the globe, 422-
424 ; selection of by man, 428 ; natural
selection of, 427, 429 ; fossil, intermediate
forms of, 424

Animals and plants, Aristotle on links
between, 16 ; history of, by Gesner,
69 ; classified by Ray and Willughby,
142 ; Linnaeus gives specific names to,
210; Buffon on distribution of, 205 ;
Grew and Malpighi on, 137-142 ; Dar-
win and Wallace on, 426

454

INDEX.

ANTIQUITY

Antiquity of man, 415 ; Lyell's work on,
418

Aphides, Bonnet on, 200

Apollo, god of the sun, 8

Apple, Newton and the, 149 ; -leaf, skin of,
showing stomates, 141

Aqueous rocks, Hutton on, 220

Arabs, conquests of the, 39 ; bum Alex-
andrian library, 39 ; science of the, 40 ;
chemistry of the, 41 ; gunpowder known
to the, 42 ; medical schools of the, 40

Arago on polarisation of light, 311 ; on
electro-magnetism, 347 ; on Biela's comet,
291

Archimedes on the lever, 22 ; on Hiero's
crown and specific gravity, 23 ; screw of,
25 ; killed in the Punic war, 25

Areas described by planets about their
centre, 100

Aristarchus taught that the earth moves
round the sun, 20 ; discovered obliquity
of ecliptic, 21 ; and rotation of the earth
on its axis, 21

Aristotelians, dogmatism of the, 81, 106

Aristotle on astronomy and zoology, 16 ;
on development of animals, 419

Arteries, passage of blood in, 11 1 ; throb-
bing of explained, 112

Articulata, term explained, 396

Asellius on lacteals and nourishing fluid,
ii4_

Astatic needle of the telegraph, 359

Asteroids, or minor planets, 289

Astrology of the Arabs, 45

Astronomy, definition of, 2 ; of Thales, 8 ;
of Anaximander, 9; of Anaxagoras, 13 ;
of Aristotle, 15 ;,of Aristarchus, 20; of
Hipparchus, 29 ; of Ptolemy, 32 ; of
Albategnius, 45 ; of Ebn Junis, 46 ; of
seventeenth century, 182-184 ; of eigh-
teenth century, 284 ; of nineteenth cen-
tury, 288

Atmosphere, refraction of sun's rays in
the, 48 ; varying weight of the, 118 ;
pressure of the, 122

Atomic theory, 374 ; difficulties of the, 376

Atoms, definition of term, 375 ; weight of
chemical, 374 ; of all the planets attract
each other, 151

Attraction, by electricity, 77, 123 ; of
gravitation decreases with square of the
distance, 152

Aurora borealis coincident with outbreak
of a sun-spot, 356

Australia, fossil and living pouched animals
of 422

BONNET

Authority valued more than truth in the

Dark Ages, 105
Avicenna on minerals, 50

BACON, Roger, his 'Opus Majus,' 52
Bacon, Francis, his influence on

science, 103 ; on heat, 330
Bagdad, medical school of, 40
Bain's telegraph, 361
Balloons, hydrogen used for filling, 231
Barometer, invention of the, 1 16-19
Bartholinus on double refraction in Iceland

spar, 180
Basalt, disputes about formation of, 219-31
Bates on species of Amazon insects, 420
Battery, first electric, 262
Becher proposes theory of Phlogiston, 135
Beddoes, Dr., employs Davy, 363
Beehive, star-cluster called the, 275
Bees, clover fertilised by, 429
Ben Musa, Arabian mathematician, 46
Bergmann on chemical affinity, 228 ; on

tests of mineral waters, 229 ; on ' fixed

air,' 230 *

Berzellius — His discoveries by electrolysis,

367 ; on use of blowpipe, 367
Betelgeux, no hydrogen in light of, 327
Bichat cited, 380
Biela's comet alarmed the world, 291 ;

divided into two, 292
Binary stars, Herschel discovers, 273
Biology, definition of, 2 ; of seventeenth

century, T85 ; spread of in eighteenth

century, 190
Blot on meteoric stone-fall, 298 ; on polari-
sation, 314
Birds, Ray and Willughby on, 144 ; rapid

multiplication of, 429
Black discovers ' fixed air,' 226-228 ; on

latent heat, 241-243 ; Young studies

under, 303
Blood, circulation of the, iJi-13; earlier

theories about, no; air-bubbles drawn

out of the, 134
Blowpipe, Berzellius on use of, 367
Blumenbach cited, 380
Bode's law, 289
Boerhaave, his character and influence,

191 ; on organic chemistry, 192 ; on

juices of plants, 193 ; on fluids of animals,

194 ; his death, 194
Bonnet's experiments on aphides and

plants, 200 ; on regrowth of severed

limbs, 201 ; on development of animals,

INDEX.

455

BOTANICAL

Botanical garden of Gesner, 6g

Botanist, Theophrastus the first, 17

Botany, different kinds of, 2 ; writers on,
17, 70, IT-, 142, 206, 381, 38s, 389

Boucher de Perthes finds ancient flint im-
plements, 415

Bougier measures the density of the earth,
278

Boulton, partner of Watt, 251

Boyle one of the founders of Royal Society,
125 ; his air-pump, 124 ; his law of com-
pressibility of gases, 128 ; his experi-
ments on air, 130

Bradley on aberration and nutation, 265

Brain described by Erasistratus, 26

Breathing, Mayow on, 132

Brewster, Sir D., on polarisation, 314 ; on
spectrum analysis, 321-23

British Museum, meteoric stones in the,
297

Bronze tools of lake-dwellings, 417

Brougham, Lord, his article against Young,

311

Bruno burnt at the stake, 83

Buckland, his Cambridge lectures, 405 ; on
glaciation of Wales, 414

BufFon, history of, 204 ; his work on na-
tural history, 205 ; and Linnaeus com-
pared, 207 ; patronises Lamarck, 389

Bunsen on dark lines in solar spectrum,
323

C^SALPINUS on plants, 71 ; on cir-
culation of the blood, in

Caesium discovered, 323

Cairo, medical school of, 40

Caloric, old term for heat, 330

Camera obscura, invention of the, 75

Camper cited, 380

CandoUe, Auguste de, on metamorphosis
of plants, 384

Capillaries discovered by Malpighl, 138

Carbonic acid obtained by Black, 226 ;
tested by Bergmann, 230 ; its nature
discovered by Lavoisier, 238

Carlisle on decomposition of water by
electricity, 364

Carnot on heat converted into motion, 338

Carrington, Mr., on outbreak of a sun-
spot, 355

Cassini on velocity of light, 173

Catastrophists in geologj', 405

Cats, their indirect influence on growth of
clover, 429

Caus' engine, 246

COLUMBUS

Cavendish discovers hydrogen, 230 ; on
composition of water, 231 ; his experi-
ment on weight of the earth, 279

Caxton the printer, 55

Cellular tissue, section of, 140

Celsius invents centigrade scale, 12c

Centigrade scale, 120

Ceres discovered by Piazzi, 289

Charles I., riots in reign of, 124 ; IL
grants Royal Society charter, 125 ; V.
of Spain protects Vesalius, 68

Chemical, rays discovered, 315 ; rays of
action in photography, 317 ; nomencla-
ture of Lavoisier, 239 ; elements, weight
of, 373 ; symbols, 376 ; or Voltaic elec-
tricity, 261 ; theory of electricity, 367

Chemical affinity, Bergmann on, 228 :
Newton on, 229 ; power of electric cur-
rent to overcome, 367

Chemistry, definition of, 2 ; of the Araos,
41 ; of Geber, 43 ; of Paracelsus and
Van Helmont, 72 ; of Boyle and Hooke,
130 ; of Mayow, 131 ; Boerhaave on 01-
ganic, 194 ; of Black, 226 ; of Bergmann,
228 ; of Cavendish, 230 ; of Priestley ,
231 ; birth of modern, 235 ; Newton's
work on, destroyed, 170 ; methods of
studying, 369

Chick, Harvey on development of, 114

Chinese, early science of, 4 ; mariner's
compass known to the, 54

Chlorale, discovery of, 378

Chloroform, "Ciscovery of, 378

Cinnamon tree, essences obtained from, 193

Cipher, word derived from Arabic, 46

Circulation of the blood, diagram of, 113

Circular polarisation in quartz crystals, 314

Circumference of earth measured by Era-
tosthenes, 28

Classifications of plants, 70-71, 142, 209,
382 ; of animals, 69, 143, 210, 396

Clausen calculates the period of Biela's
comet, 291

Clifford, Mr., befriends Linnaeus, 207

Climate, Humboldt on causes of, 385 ;
Lamarck on effects of, 393

Cod-fish, animalcules in roe of, 140

College of Surgeons, Hunter's collection
in,- 200

Colours, prismatic, 167 ; cause of in tele-
scopes, 169 ; caused by interference of
light, 307 ; on the soap bubble, 307 ;
depend on light-vibrations, 177

Columbus, Christopher, his voyages, 56 ;
discovers variation of magnetic needle,
57

456

INDEX.

COLUMBUS

Columbus on circulation of the blood, 1 1 1

Combustion, Hooke on, 130 ; Mayow on,
132 ; Stahl's mistaken theory of, 135 ;
cause of proved by Lavoisier, 238

Comet, Halley predicts return of, 163

Comets, Newton on orbits of, 155 ; re-
turning, 291 ; and meteors, 297

Commutator of the telegraph, 360

Comparative anatomy, rise of, 197 ; Hun-
ter's collection illustrating, 199 ; Haller
on, 197 ; Cuvier on, 395-98

Compass, figure of first mariner's, 54

Compound flowers, 145

Concluding remarks, 433

Condenser, Watt's separate, 248-50

Conservation of energy, 339

Contraction of the muscles, 197

Cook's voyage to observe transit of Venus,
162

Cooke patents electric telegraph, 357

Copernican theory, 65 ; proofs of the truth
of, 91

Copernicus, life and work of, 65

Cordova, medical school of, 40

Corpuscular theory of light, 174, 303

Correlation of the physical forces, 435

* Cosmos ' of Humboldt, 386

Crabtree sees transit of Venus, 158

Crookes discovers thallium, 323

Crown of cups, Volta's, 262

Crown-glass, dispersion of light in, 169

Crystals, double refraction in, 180; r-;is-
sage of light-waves in, 313 ; circular
polarisation in quartz, 314

Currents from an electric battery, 262 ;
Humboldt on ocean, 385-86

Cuvier, history of, 389-95 ; his museum,
391 ; on creation of animals, 394 ; his
discussion with St.-Hilaire, 395-397 5 on
comparative anatomy, 395 ; on classifica-
tion and structure of animals, 396 ; on
fossil animals of Paris, 397 ; his ' Osse-
mens Fossiles,' 399 ; death of, 400

Cycloidal pendulums, 175

DABURON, Ampere's visit to, 344
Daguerre fixes sun-pictures, 317

Dal ton, life of, 371 ; on law of multiple
proportions, 373 ; atomic theory, 374

Dark ages, science of, 39 et seq.

Darwin, his history, 425 ; on origin of
species, 426 ; his theory explained, 427-
431 ; on causes of natural selection, 429

Daubenton's anatomical work, 205

Dav>^ Sir H., his history, 362 ; his experi-

EARTHQUAKES

ments on nitrous oxide, 363 ; on electro-
lysis, 364 ; discovers potassium and
sodium, 365 ; his safety lamp, 363 ; on
organic chemistry, 378 ; on sun-pictures,
317 ; Sir H. melts ice by friction, 333 ;
his kindness to Faraday, 348

De Dominis on the rainbow, 164

Delisle's method of measuring transit of
Venus, 266

Deltas, growth of, 12

Democritus on the Milky Way, 15

Denudation, Hutton on, 220

Descartes on light, 106, 164 ; on the value
of doubt, 105

Development of animals, Lamarck on,
391 ; Von Baer on, 402

Diagram showing how distances can be
measured on the sun's face, 159

Diagrams of bent and broken rocks, 217,
218

Diameter of the sun, 161

Diamond, nature of, proved by Lavoisier,
238

Djafer, or Geber, Arabian alchemist, 43

Disecious plants explained by Caesalpinus,
72

Dicotyledons term explained, 145

Differential calculus, by Leibnitz, 148

Disc, Newton's rotating, 168

Dispersion of light discovered by Newton,
J64 ; in different kinds of glass, 169

Distillation known to Geber, 43, 370

Distribution of animals, Buffon on, 206 ; of
plants, Humboldt on, 385

Dogmatism of the sixteenth century, 67,
81, 83

Dollinger, anatomist, 401

Dollond, Mr., makes achromatic telescope,
169

Double refraction, 179, 180

Doubt, Descartes on the value of, 105

Drebbel makes alcohol thermometer, 120

Ducts of plants, 140

Du Faye on electricity, 254

Dynamical theory of heat, 335

EARL'S COURT, Hunter kept wild
animals at, 199
Earth declared by Aristotle to be a globe,
16 ; circumference of measured, 28 ;
Picart measures the size of the, 150 ;
Newton on shape of the, 154 ; measure-
ment of density of the, 277
Earth-light on the moon, 89
Earthquakes, Pythagoras on, 12 ; Strabo

¥

INDEX.

457

EBN

on causes of, 33 ; changes of level caused

by, 408
Ebn Junis, Arabian astronomer, 46
Eclipses explained by Anaxagoras, 13
Ecliptic or sun's path, how traced out by

the Greeks, 18 ; Anaxagoras discovers

obliquity of, 21
Egyptians, early science of, 4
Eighteenth century, work of the, 434 ;

summary of science of, 280
Elective affinities, Bergmann on, 229
Electric currents causing magnetic cur-
rents, 346 ; making electro-magnets, 347 ;

power of to conquer chemical affinity,

367 _

Electrical machines, Guericke's, 123 ;
Hawksbee's, 123

Electric spark observed by Guericke, 124

Electric telegraph, invention of, 357 ; des-
cription and diagrams of, 357-60 ; Bain's
set on fire by magnetic storm, 356 ;
Morse's and Steinheil's, 357

Electricity, Gilbert on, 77, 123 ; attraction
and repulsion by, 124 ; Du Faye on dif-
ferent kinds of, 254 ; Franklin on, 255 ;
and lightning, 256 ; positive and nega-
tive, 256 ; animal, 259 ; chemical or vol-
taic, 261 ; chemical theory of, 367 ; pro-
duced by heat, 352

Electrolysis, discovery of, 364 ; Davy's
experiments in, 365 ; Faraday on, 367

Electro-magnetism, Oersted discovers, 341 ;
Ampere on, 345 ; Faraday on, 349

Electro-magnets made by electric current,

347
* Electron,' root of word ' electricity,' 77
Elements, sixty-four known, 370
Ellipses, planets move in, 99
Embryology, Von Baer's law of, ^00 ; con-
firms St.-Hilaire's view of homological

structure, 401
Embryos of animals alike in structure, 42 r
Emission theory of light, 174, 303
Encke's comet, 290
Energy, potential and active, 337, 339 ;

conservation of, 339, 353
Engines, history of, 245 ; the Newcomen,

246 ; Watt's double-acting, 250
England, geological map of, by W. Smith,

224
Epidermis studied by Malpighi, 139
Equinoxes observed by Thales, 9 ; Hip-

parchus discovers precession of, 30
Erasistratus on the brain, 26
Erratic blocks on the Jura, 413 ; a proof of

former extension of ice, 414

21

FRENCH

Eratosthenes lays down first parallel of

latitude, 27 ; measures circumference of

the earth, 28
Ether, light a vibration of the, 176
Euclid, some problems of, invented by

Thales, 9
Euclid discovers that light travels in

straight lines, 21
Eudoxus explains movements of the

planets, 15
Eustachius the anatomist, 68
Evolution, theory of, 435
Extinct animals, restored by Cuvier, 398 ;

man contemporary with, 415
Eye, Alhazen on the sight of the, 47 ;

Porta on structure of the, 76 ; Kepler on

the, 96

FABRICIUS Aquapendente discovers
valves in veins, in

Fahrenheit thermometer, freezing point of,
120

Falling bodies, Galileo on rate of, 80

Falloplus, the anatomist, 68

Faraday, history of, 348 ; on rotation of
magnets and electric wires, 349 ; on
electric current produced by a magnet,
351 ; on connection between electricity
and chemical changes, 367

Faust, John, the printer, 55

Fire-air discovered by Mayow, 132 ; its
effect on the blood, 134

' Fixed air,' Black on, 226-228 ; Berg-
mann tests, 230

Flame consuming 'fire-air,' 132; spectra
of different kinds of, 321

Flint implements of Abbeville, 415

Flint-glass, dispersion of light in, 169

Flood, attempt to explain fossils by a
universal, 215

Flowers, plants classified by their, 145

Fluxions, Newton's method of, 148, 153

Force, convertibility of, 369 ; of gravita-
tion, 149

Fossil animals restored by Cuvier, 327 ;
intermediate forms of, 424

Fossil shells observed by Pythagoras, 11

Fossils, Gesner on, 7<3*; first attempts to
explain, 215 ; used by W. Smith for
classification, 223

Franklin's early life, 253 ; his experiments
in electricity, 255 ; he proves lightning
to be electricity, 256-258

Fraunhofer's early life, 319 ; lines, 320

French school of chemistry, 239

45S

INDEX

FRESNEL

Fresnel, history of, 311 : on polarisation
of light, 311; on circular polarisation,

314

Freyberg, Werner's lectures at, 217

Friction, ice melted and water boiled by,

333
Friendship of Ray and Willughby, 143
Frog's leg, electricity in, 259-61

GALEN, physiology of, 34 ; corrected
by Vesalius, 67
Galileo on the pendulum, 79 ; on falling
bodies, 80 ; on motion of heavy bodies, 82 ;
on secondary light of the moon, 89 ; on
Jupiter's moons, 91 ; on phases of Venus,
91 ; on sun-spots and rotation of sun on
its axis, 91 ; demonstrates the truth of
Copernican theory, 91, 102 ; his telescope,
89 ; his recantation, 93 ; his blindness
and death, 94 ; on rising of water in a
pump, 116 ; makes a water thermometer,
120 ; compared with Tycho and Kep-
ler, 102
Galle finds Neptune, 294
Galvani on animal electricity, 259 ; his
controversy with Volta, 260 ; his death,
261
Galvanism, 260

Galvanometer invented by Ampere, 351
Ganges, mud carried down by the, 407
' Gas,' term used by Van Helmont, 73 ;

Nebulae composed of, 275
Gases, Boyle's law of, 128 ; Bacon on, 52 ;
Mayow on, 132 ; discovery of the four
important, 225 ; spectra of, 322 ; atmo»
sphere of, round the sun, 325 ,
Gassendi observes transit of Mercury, 157
Gauss rediscovers Ceres, 290
Gay-Lussac on multiple volumes, 377
Geber the founder of chemistry, 43-45
Geist, word ' gas ' derived from, 73
Geography, Ptolemy's work on, 33 ; Strabo

on, 33
Geology, definition of, 2 ; of Pythagoras,
II, 215 ; neglected in dark ages, 214 ;
Lazzaro Moro on, 216 ; Werner on, 217 ;
Hutton on, 219 ; W. Smith on, 223 ; Sir
C. Lyell on, 405 ; of eighteenth century,
281 ; prejudices retarding, 404
George II. founds G5ttingen University,

196
Geranium, LInnseus's definition of the,

209
Gerbert introduces Arabic numerals into
Europe, 4$

GUTENBERG

Germ, growth of the, 141
Germany, Imperial Academy in, 126
Gesner, his life and character, 65-70 ; his

cabinet and garden, 69 ; his history ot

animals, 69 ; his botanical classification,

70
Gilbert, first experiments on electricity, 77,

123
Gioja discovers mariner's compass, 53
Glacial period, 414
Glacier, term explained, 411 ; illustration

of a, 412; of Switzerland, 413; carrying

blocks to the Jura, 413
Gladstone, Dr., his life of Faraday, 349
Glass, angle of polarisation of light from,

310 ; index of refraction for, 108 ; different

dispersive powers of, 169
Graham on variations of magnetic needle,

355

Granite, Hutton on formation of, 221 ; veins
in Glen Tilt, 222

Gravitation, law of, explained, 148-155 ;
discovered by Newton, 148 ; its action on
the planets, 151 ; attraction acts from
the centre of bodies, 150 ; decreases with
the square of the distance, 152 ; problems
explained by, 155 ; holding distant stars
together, 274

Gravity, action of, explained, 151

Glen Tilt, granite veins in, 222

Gnomon at Alexandria, 28

Gold separated from amalgam by Paracel-
sus, 72

Goethe on metamorphosis of plants, 381 ;
on discussion between Cuvier and St.-
Hilalre, 395

Gottingen University founded, 196

Gough the patron of Dalton, 371

Grsecus, Marcus, discovers gunpowder, 42

Gratz, Kepler professor at, 95

Greece, Roman conquest of, 35

Greek colonies in Ionia, 8

Greeks deficient in natural knowledge, 8 ;
believed the sun moved round the earth,
19 ; knew electric nature of amber, 77 ;
general remarks on science of the, 34

Grew on vegetable anatomy, 141 ; on
stomates, 141 ; on cellular tissue, 140

Grove cited, 434

Guerlcke's air-pump, 121 ; Magdeburg
hemispheres, 122 ; first electrical ma-
chine, 123 ; his experiments on electricity,

124
Gunpowder known to the Arabs, 42
Gutenberg, John, the printer, 55

INDEX.

459

HALES

HALES, Dr., on guses, 226 ; on water
in plants, 193

Hall, Mr. C. More, on flint and crown
glass, 169

Hall, Sir J., on melted rocks, 221

Halle, Dr., pleads for Lavoisier's life, 239

Haller, early life of, 195 ; his work with
students, 196 ; his anatomical plates, 196 ;
on contraction of the muscles, 197 ; on
comparative anatomy, 197

Halley, his method of measuring transits,
158-162 ; observes transit of Mercury,
158 ; predicts the return of a comet, 163

Harding discovers Juno, 290

Harvey discovers circulation of the blood,
no ; the opposition to his views, 113 ; on
development of the chick, 113

Hawksbee's electrical machine, 123

Heat, Bacon's examination of, 104 ; early
theories about, 329 ; produced by friction,
330 ; a vibration, 333 ; latent, 241, 334 ;
mechanical equivalent of, 336 ; Joule's
experiments on, 335-338 ; conversion of
motion into, 332-337 ; converted into
motion, 338 ; production of electricity by,
352

Heat-rays discovered, 315

Heavy bodies, Galileo on motions of, 82

Helmholtz cited, 434

Hercules, motion of our solar system to-
wards, 275

Hermes and hermetic philosophers, 41

Hero's engine, 245

Herophilus on muscles, nerves, and the
pulse, 27

Herschel, SirW., makes his own telescopes,
272 ; discovers Uranus and receives a
pension, 272 ; on binary stars, 273 ; on
star-gauging, 273 ; on nebulae, 274, 327 ;
on motion of solar system through space,
275 ; discovers heat-r«.ys, 315 ; on cause
of sun-spots, 353

Herschel, Sir J., work in astronomy, 295-
296 ; on Magellanic clouds, 295 ; his
' Outlines of Astronomy,' 296 ; on spec-
trum analysis, 322

Herschel, Miss C, her brother's assistant,
277

Herschel, Mr. A., on spectrum of falling
stars, 328

Hiero's crown, Archimedes on, 23

Higgins on chemical law of proportions,

373
Hipparchus, astronomy of, 29 ; discovers

precession of equinoxes, 30
Hippocrates the father of medicine, 14

IRIDIUM

Hirn, M., his experiments' on heat con-
verted into motion, 338
Hodgson, Mr., on outbreak of a sun-spot,

355

Homology, St.-Hilaire on, 394

Hooke one of the founders of the Royal
Society, 125 ; on air-pump, 128 ; on com-
bustion, 130 ; on geology, 216

Horrocks observes transit of Venus, 157

Huen island, Tycho's observatory on, 78

Huggins, Dr., on spectrum analysis of the
stars, 326 ; of nebulae, 327

Human anatomy, Vesalius on, 67

Humboldt, history of, 384 ; on isothermal
lines, 385 ; on distribution of plants, 385 ;
his ' Cosmos,' 386 ; on meteors, 297 ;
pays expenses of Agassiz's work, 410

Hunter, John, his birth and history, 19S ;
on comparative anatomy, 198 ; his mu-
seum, 199

Hutton on geology, 219-23 ; on granite
veins, 222 ; and Werner, 222 ; on size
and weight of Schehallien, 279

Huyghens, history of, 175 ; invents cycloi-
dal pendulum, 175 ; describes Saturn's
ring, 175 ; his undulatory theory of light
explained, 175, 181 ; on refraction of
light, 178 ; on double refraction, 179

Huxley on fossil bird-reptile, 424 ; on
rapid multiplication of plants, 429

Hydrogen discovered by Cavendish, 230 ;
name given by Lavoisier, 239 ; amount
of in water, 372

ICE, heat lost in melting, 242 ; melted
by friction, 333 ; rocks scratched and

blocks carried by, 413 ; -period in the

northern hemisphere, 411
Iceland spar, double refraction in, 180
Igneous rocks, Hutton on, 220
Imperial Academy of Germany founded,

126
Index of refraction, 108
Indians, early science o^ 4
InductioD-coil, 351
Inquisition banishes Vesalius, 68 ; bums

G. Bruno, 83 ; forces Galileo to recant,

93
Insects, Ray's work on, 144 ; microscopic

anatomy of, 139
Interference of light, 304-6 ; colours caused

by, 307
Invertebrate animals, Lamarck on, 391
Ionian school of learning, 8
Iridium discovered, 323

460

INDEX,

IRON

Iron tools of lake-dwellings, 417
Islands, formation of, 12
Isothermal lines, Humboldt on, 3S5
Italy, early scientific societies in, 126

JAMES, Sir H., on weight of the earth,
280
Jansen makes a telescope, 87
Jews, medical knowledge of the, 39
Joule, Dr., experiments on the mechanical

equivalent of heat, 335-338
Juno discovered, 290
Jupiter, atmosphere of, 327 ; his moons,

90 ; velocity of light measured by, 172 ;

and Saturn, long inequality of, 269
Jura mountains, erratics of the, 413
Jussieu's natural system of plants, 211,

382

KENT'S Hole, flint implements in,
416

Kepler, life and difficulties of, 95, loi ; on
structure of eye, 96 ; his telescope, 97 ;
his first law, 97 ; second law, 99 ; third
law, 100 ; his delight at Galileo's dis-
coveries, IOC ; on refraction, 100 ; pre-
dicted transits of Mercury and Venus,
157 ; finished Rudolphine tables, loi ;
compared with Tycho and Galileo, 102

Kew gardens, 208

Kircher invents magic lantern, 76

KirchhofF on dark lines in solar spectrum,
323 ; his spectroscope, 324

Kite, Franklin's, 257

Koran forbade dissection, 40

LACTEALS discovered by Asellius,
114
Lagrange, 266 ; on libration of the moon,

267 ; on stability of planetary orbits,

270
Lake- dwellings of _ Switzerland, 416; tools

and food found in, 417
Lamarck, history of, 389 ; on invertebrates,

391 ; on development of animals, 391 ;

his 'Philosophie Zoologique,' 393 ; weak

point in his theory, 393
Lamont on variations of magnetic needle,

355
Land, conversion of, into sea, 11
Laplace, 267 ; on long inequality of Jupiter

and Saturn, 269 ; on moon's acceleration,

270 ; on heat, 336

LINN^US

Lassell on Neptune's moon, 295

Latent heat. Black on, 241 ; of water, 243 ;
theory of, applied by Watt, 244, 248 ;
explained, 334

Latitude, first parallel of, laid down, 27

Laughing-gas, Davy's experiments with,
363 _

Lavoisier the founder of modem chemistry,
235 ; his experiments, 237 ; his death, 239

Law of compressibility of gases, 128 ; of
definite proportions in chemistry, 372 ,
of multiple proportions, 373 ; of gravita-
tion, 151 ; of refraction discovered by
Snellius, 107

Laws of Kepler, 97, 99, 100

Leaves of plants. Bonnet on use of, 200

Leeuwenhoeck on animalcules, 139

Leibnitz on differential calculus, 148

Lenses, magnifying power of convex, 49 ;
Alhagen on use of, 48 ; Porta on, 76 ;
Galileo on, 88 ; Kepler on, 96

Leslie, Sir J., on refraction of heat, 340

Lever, Archimedes on the, 22

Leverrier calculates the position of Nep-
tune, 292, 294 ; on November meteors,
299

Leyden, medical school of, 190

Libration of the moon, 267

Liebig on organic chemistry, 377

Light, Euclid on rays of, 21 ; a vibration,
176 ; causing colour, 177 ; polarization
of, 181, 309 ; compared to sound, 176,
178 ; dispersion of, 164, 167 ; blending
of colours into white, 168 ; interference
of, 302-306 ; bands of, in shadows, 304 ;
undulations compared to waves of a
pond, 306 ; reflection of from a soap-
bubble, 308 ; complex vibrations of, 312 ;
passage of through a crystal, 313 ;
Roemer measures velocity of, 172 ;'
theories of, 174, .303 ; undulatory theory
explained, 174-179

Lightning, electric nature of proved by
Franklin, 256 ; conductors, 258

Lilienthal, meeting of astronomers at, 289

Limestone, fixed air obtained from, 226 ;
beds of Sicily, thickness of, 407

Lines in the spectrum, 318, 320 ; their
cause explained, 323

Linnsean system, 210; collection brought
to England, 212

Linnaeus, early life of, 205, 207 ; and BufFon
compared, 207 ; his ' Excursions,' 208 ;
gives specific names to plants and
animals, 208 ; creates an accurate nomen-
clature, 211 ; modifies Ray's system.

INDEX.

461

LIPPERSHEY

145 ; on metamorphosis of plants, 383 ;
death and character of, 212
Lippershey makes a telescope, 87
Lithuanian legend about falling stars, 297
Loadstone known to the Greeks, 53
Locke on heat, 330

Lockyer on spectrum analysis of stars, 326
Locomotive-engine, date of first, 245
Looking-glass, cause of reflection of, 177
Lungs, circulation of blood through the,

112 ; studied by Malpighi, T38
Luxembourg Palace, polarized light re-
flected from windows of, 310
Lyell, Sir C, his history, 405 ; on present
causes of geological change, 406-410 ; his
influence on geology, 409 ; on Darwin's
work, 426
Lymphatics discovered by Riidbeck, 1 15 .

MAC ENERYon flint implements of
Kent's Hole, 416

Magdeburg hemispheres, 122

Magellan's ship sails round the world, 57

Magellanic clpuds, 295

* Magia Naturalis ' published, 74

Magic lantern invented, 76

Magnet, origin of name, 53 ; producing
electric current, 350 ; and electric wires,
mutual rotation of, 349 ; diagram of,
350

Magnetic currents caused by electric cur-
rents, 346 ; direction of, 345 ; affected by
sun-spots, 355 ; needle, variations of the,
57 ; affected by electric current, 343,
345 ; Ampere on direction of, 345 ; sudden
movement of at Kew, 355 ; periodical
shifting of the, 355 ; of electric telegraph,

359
Magnetism, Gilbert on, 77 ; electro-, 341-
352 ; terrestrial affected by sun-spots,

353

Magnifying glasses explained, 49

Malpighi applies the microscope to living
structures, 137 ; history of, 13S ; on air-
cells, 138 ; discovers Malpighian layer,
139 ; on silkworm, 139 ; on structure of
plants, 140 ; on growth of germs and
seeds, 141

Malus on polarization of light, 309

Man, antiquity of, 413 ; selection of animals
by, 428

Map made by Anaximander, 10 ; geologi-
cal, made by W. Smith, 224

Marcus Grsecus, gunpowder made by, 43

Mariner's compass, 53

MOON

Marquis of Worcester's engine, 246

Marriotte's law, 130

Mars, atmosphere of, 327 ; movements of

explained by Kepler, 97 ; occultation of

observed by Aristotle, 16
Maskelyne measures the density of the

earth, 277
Maury on division of Biela's comet, 292
Mayer, Dr., on mechanical equivalent of

heat, 335
Mayow a conscientious observer, 131 ; he

discovers 'fire-air,' 132 ; his experiments

on combustion and respiration, 132 ; his

early death prevented his theory being

known, 135
' Mecanique Celeste ' of Laplace, 271
Mechanical equivalent of heat, 336
Mechanics, definition of, 2
Medical school of Leyden, 190
Medicine, Hippocrates the father of, 14 ;

Galen on, 34
Melloni on passage of heat rays, 340
Men of science, lists of, 6, 38, 62, 86,

188
Mercurial thermometer, how made, 120
Mercuric oxide, Priestley obtains oxygen

from, 233
Mercury obtained from cinnabar by Geber,

44 ; sustained in a tube by weight of air,

118 ; combining with ox3'^gen, 373
Mercury, transits of observed, 157-158
Metals, Geber notices increased weight of

heated, 44 ; electric discharge from two,

261 ; discovered by spectrum analysis,

322
Metamorphosis of plants, 381
Meteors and their paths, 297-300 ; their

composition, 297 ; spectrum analysis of,

328
Microscope applied to living structures,

137 ; definition of, 137
Middle ages, science of the, 39-59
Milky Way studied by Democritus, 15 ;

by Galileo, 90
Miller, Dr., on spectrum analysis of the

stars, 326
Mineral waters analysed by Bergmann,

229
Mineralogy, Gesner on, 70 ; Werner's

lectures on, 217
MoUusca, term explained, 396
Monocotyledons, term explained, 145
Monro cited, 380
Mont Blanc, erratic blocks carried from,

413
Moon, Anaxagoras on the, 13 ; phases of

462

INDEX.

MOONS

explained by Anaximander, 10 ; Thales
on reflection of the, 9 ; secondary light
of the, 89 ; movement of used by New-
ton to test his law of gravitation, 150 ;
Lagrange on libration of, 267 ; why she
turns the same face to us, 268
Moons, Jupiter's, 90
Moraines of glaciers, 412
Moro, Lazzaro, on formation of strata, 216
Morse, his electric telegraph, 356, 361
Mother-of-pearl, cause of colours in, 309
Motion, conversion of, into heat, 332, 337
Mountain-chains, Eratosthenes studies, 29
Mouse consuming air in a bell-jar, 132
Mud carried down by the Ganges, 407
Murchison cited, 407

Muscles, Haller on contraction of the, 197
Musical notes, Pythagoras on, 12

ATAPOLEON I. takes St.-Hilaire to

-i M Egypt, 391

Natural history of seventeenth century,

137-145 . . .

Natural philosophy, Leonardo da Vmci on,

58

Natural selection, theory of, 426-428 ; ob-
jection to the theory of, 428 ; difficulties
of natural history explained by, 431 ;
does not exclude Divine Power, 432

Natural system of plants, 211, 382

Nebulae, Herschel on the nature of, 275 ;
spectrum analysis of, 327

Nebular hypothesis, 271

Negative and positive electricity, 256, 262

Negro, colouring matter in skin of, 139

Neptune, position of found by Adams and
Leverrier, 292 ; seen by Galle, 294 ; his
moons, 295

Neptunists and Vulcanists, 218

Nerves, Galen on two sets of, 34

Nestorians, science of the, 40

Neuchatel, erratic block near, 413

Newcomen's engine, 246

Newt, re-growth of eye of, 202

Newton, birth and early life of, 14 ; his
law of gravitation, 148-155, 183 ; his
method of fluxions, 148 ; on variation of
attraction, 152 ; on cause of tides, 154 ;
on specific gravity of planets, 154 ; 01^
shape of the earth, 154 ; on precession of
equinoxes, 154; on motion of comets,
155 ; on sound, 175 ; on chemical attrac-
tion, 229 ; on attraction of plumbline to
a mountain, 278 ; on light and colour,
148 ; on dispersion of light, 164, 185 ex-

PAPIN

plains the spectrum, 166 ; and compound
nature of light, 165-167 ; his rotating
disc, 168 ; his work on chemistry de-
stroyed, 170 ; his work on optics, 169 ;
his theory of light, 174, 303 ; his charac-
ter and death, 170

Newton, Prof., on falling stars, 229

Nicholson on decomposition of water by
electricity, 364

Nile, mud carried down by, 11

Nineteenth century, tendency of science of,

434
Nitrogen, compounds of oxygen with, 373 ;

Rutherford on, 235
Nitrous oxide, Davy's experiments on, 363
Nobili on animal electricity, 261
' Novum Organum,' 103
Numerals, Indian, introduced into Europe,

46 _
Nutation of earth's axis, 266

OBLIQUITY of ecliptic, Anaxagoras
on, 21
Observatory, Tycho's, 79
Oersted on electro-magnetism, 341
Olbers, Dr., discovers Pallas and Vesta,

290
Optics, Alhazen on, 46 ; Porta on, 76 ;

Kepler on, 96 ; Newton's work on. 169
'Opus Majus ' of Roger Bacon, 51
Orbits of the planets, elliptical, 98 ; do not

all lie in the same plane, 99 ; governed

hy gravitation, 151
Organic chemistry, foundation of, 190 ;

Liebig on, 377
Organic sciences of nineteenth centui-y too

difficult to follow, 380
Organs, of digestion arranged by Hunter,

199 ; modification of, 381 ; St. Hilaire on

modification of, 393
* Ossemens Fossiles ' published, 399
Ovid's 'Metamorphoses,' 11
Oviparous and viviparous animals, 143
Oxford, early meetings of Royal Society

at, 125
Oxygen called ' fire-air ' by Mayow, 134 ;

discovered by Priestley and Scheele, 231-

234 ; amount of in water, 372 ; compounds

of with nitrogen, 373

I'^ADUA, Professors of, 67, 71, 81, no
Palissy on fossil shells, 215
Pallas discovered, 290
Papin's engine, 246

INDEX.

46J

PARABOLAS

Parabolas described by comets, 155

Paracelsus, chemistry of, 72

Paris, Cuvier on fossil animals of, 397

Pascal on pressure of the amosphere, 119

Pecquet on thoracic duct, 114

Pericles pleads for Anaxagoras, 14

Perrier, M., carries a barometer up the

Puy de Dome, 119
Pendulum, Galileo on the, 79
Phases of moon, 10 ; of Venus, 91
Philosopher, name first given to Pytha-
goras, 12
Philosophical transactions begun, 127
Phlogiston, theory of, 135 ; destroyed by

Lavoisier, 238
Photography explained, 317
Physics, definition of, 2 ; of sixteenth cen-
tury, 83 ; of seventeenth century, 114 ;
of eighteenth century, 282
Physical, forces, correlation of the, 435 ;

geography, Humboldt on, 386
Physiology, beginning of the study of,

110-115
Piazzi discovers Ceres, 289
Picart, size of the earth measured by, 150
Pierre-a-Bot, an erratic block, 413
Pigeons, common descent of different

varieties of, 392
Pisa, Galileo and the men of, 81
Pith of elder, cells in, 140 ; ball attracted
and repelled by rubbed sealing-wax, 124
Planets, Anaxagoras on, 14 ; Eudoxus on,
^, 15; Kepler's laws concerning the, 97-
K 100 ; held in their orbits by gravitation,
H rsi ; minor, or asteroids, 289 ; stability
B of their orbits proved by Lagrange, 270 :
^ their weight and size calculated by
Leverrier, 294
Plants, Aristotle on low organisation of,
16 ; Theophrastus on, 17 ; microscopic
structure of, 140 ; ashes of, examined by
^ Boerhaave, 193 ; Hales on breathing of,
^^ 193 ; Bonnet on leaves of, 200 ; Gesner
^^t on, 70; Csesalpinus on, 71 ; Ray on, 142 ;
^H> Linnseus, artificial system of, 208 ;
^^ Jussieu, natural system of, 211, 382 ;
specific names given to, 209 ; Humboldt
on distribution of, 385 ; metamorphosis
of, 381 ; Priestley on breathing of, 232
Playfair's illustrations of Hutton, 219
PolarizsSion of light, 181 ; by reflection,

309 ; circular, 314
Porta, his meetings in Naples, 74 ; his
camera obscura, 75 ; on the eye, 76 ; his
engine, 246
Positive and negative electricity, 256, 262

RED

Potassium discovered by Davy, 365
Potter, Humphrey, ties the engine-cocks

247
Ptolemaic system, 32
Ptolemies patrons of learning, 18
Ptolemy, astronomy of, 32 ; geography of,

33 ; 'cloudy stars ' seen by, 274
Precession of equinoxes discovered by

Hipparchus, 30 ; Newton on, 154
Pressure and volume, relations of, 130
Prestwich on flint implements, 416
Priestley, his discoveries, 232 ; calls oxygen
' dephlogisticated air,' 234 ; his troubles
and death, 235
Prism, light dispersed in a, 165
Prismatic colours, Newton on, 167
' Principia,' some problems discussed in

the, 153
' Principles of Geology ' published, 410
Printing, invention of, 55
Proctor on shooting stars, 299
Proportions, law of definite, 373
Proust on chemical law of proportions, 373
Pulmonary circulation of the blood, 113
Pulse studied by Herophilus, 27
Pump, height that water will rise in, 117
Pythagoras, science of, 11, 215
Pythagorean system, 21

QUADRANT made by Copernicus, (i()
Quadrupeds, Ray's work on, 143
Quicklime, nature of, 226

RABBITS descended from one wild
stock, 392
Radiata, term explained, 396
Rain, denuding effects of, 406
Rainbow, De Dominis on, 164
Ramsay, Prof., cited, 218
Ray, on geology, 216 ; and Willughby,
history of, 142 ; on quadrupeds, 143 ; on
birds, fishes, and insects, 144 ; on plants,

145
Rays of light, index of refraction of, 108 ;
Euclid on, 21 ; Alhazen on refraction of,
47 ; Kepler on, 96 ; Young and Fresnel
on, 305-309 ; Newton on refraction of
coloured, 166 ; non-interference of ordi-
nary and extraordinary, 312 ; paths of
through a crystal, 313 ; discovery of
chemical and heat, 315
Reaumur's scale, freezing point of, 120
Red fire made by burning strontium, 322

464

INDEX.

REFLECTION

Reflection of light, 177 ; polarization of
light by, 309

Refraction explained by Alhazen, 47 ; ex-
plained by Huyghens, 178 ; figures illus-
trating, 179 ; double, 179, 180 ; Snellius
discovers law of, 106 ; method of mea-
suring, 108 ; of coloured rays, 166 ;

'Regne Animal,' Cuvier's, 397

Reptiles, gigantic fossil, 423

Repulsion by electricity, 124

Respiration, Boyle on air used in, 131 ;
Mayow on effects of fire-air in, 134

Richter on chemical law of proportions,
373 ; and Reich discover iridium, 323

Rieban, Mr. Faraday's master, 348

Ritter discovers chemical rays, 315

Rivinus on plants, 209

Robison on Watts, 245

Rocks, diagrams of, bent and broken, 218 ;
new ones formed out of old, 220

Roe of codfish, animalcules in, 140

Roemer measures velocity of light, 172

Roger Bacon makes gunpowder, 52 ; his
experiments on air, 52

Ronald's, Mr., attempt at electric tele-
graph, 356

Rose, modification of parts in the, 382 ;
number of species of, 420

Rothmann, Dr., befriends Linnseus, 205,
207

Royal Institution, Young professor at, 303 ;
Davy at, 363 ; Faraday at, 348

Royal Society founded, 125 ; early mem-
bers of, 127 ; Newton learns tlie real
size of the earth at the, 150 ; Halley's
method proposed to the, 158

Rubidium discovered, 323

Rudbeck discovers lymphatics, 115

Rudimentary organs, 421

Rudolph II. protects Tycho and Kepler,

79. 95 _

Rudolphine tables, 79, loi ; used to pre-
dict transits, 157

Rumford, Count, his history, 330 ; pro-
duces heat by friction, 331 ; appoints
Davy to Royal Institution, 363

Rutherford, Dr., on nitrogen, 235

SABINE, Sir E., on connection between
sun-spots and magnetic currents, 355 ;
on weight of our earth, 280
St.-Hilaire, G., history of, 390 ; on Egyp-
tian animals, 391 ; on homologous parts
of animals, 393 ; his discussion with
Cuvier, 395

SLOUGH

Salamanders, regrowth of limbs of, 201

Sal-ammoniac known to the Arabs, 45

Salerno, medical school of, 40

Salt, colour of burning, 322

Salts of plants extracted, 193

Sap, Ray and Willughby on, 143

Satellites of Jupiter, 90 ; eclipses of, 173

Saturn, atmosphere of, 327 ; weight of, 154 ;
his ring seen by Galileo, 92 ; and Jupiter,
long inequality of, 269

Saussure, De, on glaciers, 412

Savery's engine, 246

Scheele, discoveries of, 232 ; on chemical
rays of light, 316

Schehallien experiment, 277 ; diagram of,
279

Schiaparelli on August meteors, 298

Schoeffer, Peter, the printer, 55

Schwabe on periodicity of sun-spots, 354

Science, definition of, 1 ; of the Greeks,
7 ; decay of Greek, 35 ; of the Middle
Ages, 39, 59 ; of the Arabs, 39, 50 ; rise
of modem, 63 et seq. ; of sixteenth cen-
tury, 82 ; seventeenth century, 182 ;
eighteenth century, 280 ; academies of,
124 ; lists of chief men of, 6, 38, 62, 86,
188, 286

Scilla on Calabrian fossils, 216

Scotland, glaciation of, 414

Screw of Archimedes, 25

Sea, land eaten away by the, 406, 408

Seasons caused by obliquity of ecliptic, 20

Section of the skin, 139

Seebeck, Professor, discovers thermo-elec-
tricity, 352

Seeds and germs, growth of compared,
141 ; classification of plants by, 71

Seguin, M., on mechanical equivalent of
heat, 335

Selection of animals by man, 428 ; Natural,

429 _
Serapis, rise and sinking of temple of, 408
Seirvetus on circulation of blood, iii
Seventeenth century, characteristic work

of, 433 ; summary of science of the, 182,

186
Shooting-stars, a legend concerning, 297
Sicily, thickness of limestone rocks in, 407
Silkworm, Malpighi on structure of, 139
Simpson, Dr., on chloroform, 378
Sines of incident and refracted rays, 109
Sixteenth century, advance of science in

the; 82, 433
Skaptar Jokul, torrent of lava from, 408
Skin, section of, 139
Slough, Herschel's observatory at, 273, 295

INDEX.

465

SMITH

Smith, Sir E., brings Linnsean collection

to England, 213
Smith, William, surveys England, 223
Snails, regrowth of parts in, 201
Snellius discovers law of refraction, 106
Soap-bubble, Newton on the, 169 ; cause

of colours on the, 307
Soda, composition of, 376
Sodium discovered by Davy, 365 ; power

of to decompose water, 375 ; spectrum

of, 322 ; KirchhofTs experiments with

vapour of, 325
Soho, manufactory of engines at, 251
Soil, substances taken from by plants,

193

Solar, spectrum, dark lines in, 318 ; and
star-spectrum compared, 321 ; system,
motion of through space, 275

Solstices observed by Thales, 9

Sound, Newton on, 175 ; light compared
to, 176, 178

Spallanzani on regrowth of severed limbs,
201

Specific gravity first measured by Archi-
medes, 23

Specific names given by Linnseas, 208

Sptctra, table of, 320

Spectrum studied by Newton, 165 ; dark
lines on the, 318, 320 ; their cause ex-
plained, 323 ; of different substances,
321 ; of gases, 322 ; of solids, 322

Spectrum analj'sis, history of, 315-28 :
metals discovered by, 323 ; of sunlight,
323 ; of stars, 326 ; of nebulae, 327 ; of
meteors, 328 ; use of in chemistry, 370

Spencer, Herbert, on evolution, 435

Spirit, Arabian name for gas, 42

Spirits of wine made by Geber, 44

Spots on the sun, periodicity of, 354

Stahl's work in chemistry, 135 ; on phlo-
giston, 135

Ctar, morning and evening, 11 ; -clusters
and nebulas, Herschel on, 274 ; -gauging
by Sir W. Herschel, 273

Stars, binary, 273 ; spectrum analysis of
the, 326

Statics, Stevinus on, 82

Steam, condensation of, 249 ; latent heat
of, 243

Steam-engine, history of the, 245 ; New-
comen's, 246 ; Watt's, 249

Steinheil on electric telegraph, 357; on
earth acting as return wire, 358

Steno on fossils in the earth's crust, 215

Stereoscope, Sir J. Herschel on the, 320

Stevinus on statics, 82

THERMOMETER

Stokes, Professor, on dark lines in solar

spectrum, 323
Stomachs of animals, peculiarities of, 199
Stone tools of lake-dwellings, 417
Strabo on earthquakes and volcanoes, 33
Strata of England mapped by W. Smith, 223
Striae caused by glaciers, 413
Struve on Neptune's moons, 295
Sublimation described by Geber, 44
Suction-tube, section of a, 117
Sulphuric acid made by Geber, 45
Summary of science of sixteenth century,
82 ; of seventeenth century, 182 ; of
eighteenth century, 280
Sun, experiment to explain the movement
of the earth round the, 19 ; seen after
setting by means of refraction, 48 ; ro-
tation on its axis proved by Galileo, 92 ;
his distance 108 times his diameter, 159 ;
method of measuring the diameter, 159-
161 ; distance from the earth, 162 ; holds
the planets round It by gravitation, 152 :
meteors falling into, 300 ; atmosphere of
vapours surrounding the, 325 ; spectrum
of the light of, 318
Sun-dial invented by Anaximander, 10
Sun-spots seen by Galileo and Harriot, 92 ;
Sir W. Herschel on cause of, 353 ;
Schwabe on periodicity of, 354 ; their
connection with magnetic currents, 355
Switzerland, glaciers of, 412 ; lake-dwel-
lings of, 416
Syene, earth's circumference measured

from, 29
Syntaxis of Ptolemy, 32
Synthesis, term explained, 371
' System of the World,' by Galileo, 93
' Systema Naturae ' published, 211

TALBOT, Fox, on sun-pictures, 317 ; on
spectra of flames, 323
Telegraph (see electric telegraph)
Telescope, Roger Bacon's idea of, 52 ; in-
vention of the, 87 ; Galileo's, 89 ; Kepler's,
97 ; achromatic, 169
Tessier, Abbe, meets Cuvier, 390
Tests, Bergmann on chemical, 229
Thales, science of, 8
Thallium discovered, 323
Theophrastus the first botanist, 17
Theories about living beings, 381
Theory of the ' Earth ' published, 219
Thermo-electricity, discovery of, 352
Thermometer, invention of the, lac

466

INDEX.

THOMPSON

Thompson, Benjamin {see Rumfoi'd)
Thomson, Dr., on Dalton's theory, 377 ;

Sir W. cited, 323, 434
Thoracic duct, Pecquet on the use of, 114
Tides, Newton on cause of, 155
Torricelli on weight of atmosphere, 117 ;

invents barometer, 118
Torricellian vacuum, 119
Tournefort's classification of plants, 145
Tower, Hunter dissects the wild beasts of

the, 198
Transits of Mercury and Venus, 156-63 ;

Halley's method of measuring, 160 ; De-

lisle's method of measuring, 266; dia-*

grams of, 160^61 ; expeditions, 162
Transparency of glass, cause of, 177
Trianon, Jardin de, 208
Truth, our want of faith In the power of,

436
Tycho Brahe, his life and astronomical

work, 78 ; Galileo and Kepler compared,

102
Tychonic system, 78
Tylor, E. B., illustrations of refraction of

light, 178
Tjmdall, Dr., on heat, 340

UNDULATORY theory of light, 175,
303 ; explains Interference, 305
Uniform action of geological change, 409
Upsala, Linnseus's botanical garden at,

208
Uranlenburg, Tycho's observatory at, 79
Uranus, discovery of, 272; its irregular
movements lead to discovery of Neptune,
292-294

T 7ACUUM, Torricellian, 119
» Valleys, excavation of, 11
Valves in veins discovered by Fabricius,

III ; use of, 112
Van Helmont, chemistry of, 72
Varieties, useful ones alone survive, 430
Vasco de Gama sees southern stEirs, 57
Vegetable anatomy, 140
Veins, Galen on, 34 ; action of discovered

by Harvey, iii; valves in, discovered

by Fabricius, in
Velocity of light measured, 172
Venus, phases of, agree with Copernican

theory, 91
Venus, transits of, 147 ; used to measure

sun's distance, 158 ; Halley's method of

measuring, 160 ; diagrams illustrating.

WILLIAM

159, 160, 161 ; Delisle's method of

measuring, 266
Vertebrata, term explained, 396
Vesalius, his work in anatomy, 67 ; ban-
ishment and death of, 68
Vessels and fibres of plants, 140
Vesta discovered, 290
Vibrations, light a series of, 176 ; of light

complex, 313
Vinci, Leonardo da, inventions of, 58
Vital fluids, belief of alchemists in, 192 ;

spirits, belief in, no
Vitelllo on refraction, 106
Viviparous and oviparous animals, 143
Volcanoes, Pythagoras on, 12 ; mass of

lava throv/n out from, 408
Voltaic electricity, 261 ; pile, 263
Volta on electricity, 261 ; his crown of

cups, 262 ; his controversy with Galvani,

260
Volume and pressure, relations of, 130
Von Baer on embryology, 400
Voyages round the world, 56
Vulcan, god of volcanoes, 7
Vulcanists and Neptunlsts, 218

WALES, moraines and erratic blocks
of, 44

Wallace, Mr. A. R., figures drawn by, 97 ;
on natural selection, 425, 426 ; on pro-
lificness of birds, 429

Wallis, Dr., his description of the Royal
Society, 125

Water, composition of, 231, 239, 372 ;
rising in a vacuum, 117 ; latent heat of,
243 ; boiled by friction, 332 ; rise of
temperature in by friction calculated,
336 ; decomposed by sodium, 375

Watt, his early life, 244 ; not the first to
make a steam-engine, 245 ; his separate
condenser, 248 ; his double-acting engine,
250 ; his partnership with Boulton, 251

Wave-theory of light, 175 ; explains inter-
ference, 305

Waves of light in a crystal, 313

Wedgwood, Dr. T., on sun-pictures, 317

Weight of bodies explained by gravitation,
154 ; of chemical elements, 373

Wenzel on law of definite proportions, 373

Werner on rocks and fossils, 217

Westminster Abbey, Newton buried in,
171

Wheatstone patents electric telegraph, 357

William of Orange founds Leyden Univer-
sity, 191

4

INDEX.

467

WILLUGHBY

Willughby and Ray, 142 ; death of, 143 ;

on classification of animals, 143
WoKler on organic chemistry, 377
Wolff on metamorphosis of plants, 383
Wollaston, Dr., observes dark lines in the

spectrum, 318
Woodward, his geological collection, 216
Woolsthorpe, birthplace of Newton, 147
World, first voyages round the, 56
Worm, regrowth of divided parts of the.

ZOOLOGY

YEAR, length of calculated, 45
Young, Dr., his life, 303 ; on inter-
ference of light, 304-306 ; and Fresnel on
polarisation of light, 311

ZODIAC, or circle of animals, 19
Zoology, Aristotle on, 16 ; Gesner on,
69 ; Ray and Willughby on, 143 ; Lin-
naeus on, 210 ; Cuvier, St.-Hilaire, and
Goethe on, 391 et seg. ; Darwin on, 426

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combined with such simplicity. — Eastern Press.

VJII.

Animal Locomotion;

Or, WALKING, S\VIMMING, AND FLYING.

With a Dissertation on Aeronautics.

By J. BELL PETTIGREW, M. D., F. R. S., F. R. S. E.,
F. R.C. P.E.

I vol., i2mo Price, $1,75.^

" This work is more than a contribution to the stock of entertaining knowledge,
though, if it only pleased, that would be sufficient excuse for its publication. But Dr.
Pettigrew has given his time to these investigations with the ultimate purpose of solv-
ing the difficult problem of Aeronautics. To this he devotes the last fifty pages of hi«
book. Dr. Pettigrew is confident that man will yet conquer the domain of the air."—'
N. Y. Jotirnal of Commerce.

" Most persons claim to know how to walk, but few could explain the mechanictij
principles involved in this most ordinary transaction, and will be surprised that the
movements of bipeds and quadrupeds, the darting and rushing motion of fish, and the
erratic flight of the denizens of the air, are not only anologous, but can be reduced to
similar formula. The work is profusely illustrated, and, without reference to the theory
it is designed to expound, will be regarded as a valuable addition to natural history.''
'—Omaha Republic.

D. APPLETON & CO., Publishers, 549 & 551 Broadway, N. Y,

opinions of the Press on the ^^International Scientific Series"

IX.

Responsibility in Mental Disease.

By HENRY MAUDSLEY, M. D.,

Fello.y of the Royal College of Physicians; Professor of Medical Jurisprudence
in University College, London.

I vol., i2mo. Cloth. . •. Price, $1.50.

" Having lectured in a medical college on Mental Disease, this book has been a
feast to us. It handles a great subject in a masterly manner, and, in our judgment, the
positions taken by the author are correct and well sustained." — Pastor aftd People.

" The author is at home in his subject, and presents his views in an almost singu-
larly clear and satisfactory manner. . . . The volume is a valuable contribution to one
of the most difficult, and at the same time one of the most important subjects of inves-
tigation at the present day." — N. Y. Observer.

" It is a work profound and searching, and abounds in wisdom." — Pittsburg Co7n~
inercial.

" Handles the important topic with masterly power, and its suggestions are prac-
tical and of great value." — Providence Press.

X.

The Science of Law.

By SHELDON AMOS, M. A.,

Professor of Jurisprudence in University College, London; author of "A Systematic

View of the Science of Jurisprudence," " An English Code, its Difficulties

and the Modes of overcoming them," etc., etc.

I vol., i2mo. Cloth Price, $1.75.

"The valuable series of 'International Scientific* works, prepared by eminent spe-
cialists, with the intention of popularizing information in their several branches of
knowledge, has received a good accession in this compact and thoughtful volume. It
is a difficult task to give the outlines of a complete theory of law in a portable volume,
which he who runs may read, and probably Professor Amos himself would be the last
to claim that he has perfectly succeeded in doing this. But he has certainly done much
to clear the science of law from the technical obscurities which darken it to minds which
have had no legal training, and to make clear to his ' lay ' readers in how true and high a
sense it can assert its right to be considered a science, and not a mere practice." — Thi
Christian Register.

"The works of Bentham and Austin are abstruse and philosophical, and Maine's
require hard study anda certain amount of special training. The writers also pursue
different lines of investigation, and can only be regarded as comprehensive in the de-
partments they confined themselves to. It was left to Amos to gather up the result
and present the science in its fullness. The unquestionable merits of this, his last book,
are, that It contains^ a complete treatment of a subject which has hitherto been handled
by specialists, and it opens up that subject to every inquiring mind. ... To do justice
to ' The Science of Law' ^yould require a longer review than we have space for. We
have read no more interesting and instructive book for some time. Its themes concern
every one who renders obedience to laws, and who would have those laws the best
possible. The tide oHegal reform which set in fifty years ago has to sweep yethighei
If the flaws In our jurisprudence are to be removed. The process of change cannot be
better guided than by a well-informed public mind, and Prof. Amos has done great
service in materially helping to promote this end." — -Buffalo Courier.

D. APPLETON & CO., Publishers, 549 & 551 Broadv/ay, N. Y.

opinions of the Press on the ^'■International Scientific Series.'^

XI.

Animal Mechanism,

A Treatise on Terrestrial and Aerial Locojnotion.

By E. J. MAREY,

Professor at the College of France, and Member of the Academy of Medicine,

With 117 Illustrations, drawn and engraved under the direction of the author-

I vol., i2mo. Cloth Price, $1.75

" We hope that, in the short glance which we have taken of some of the most im-
portant points discussed in the work before us, we have succeeded in interesting our
readers sufficiently in its contents to make them curious to learn more of its subject-
matter. We cordially recommend it to their attention.

"The author of the present work, it is well known, stands at the head of those
physiologists who have investigated the mechanism of animal dynamics — indeed, we
may almost say that he has made the subject his own. By the originality of his con-
ceptions, the ingenuity of his constructions, the skill of his analysis, and the persever-
ance of his investigations, he has surpassed all others in the power of unveiling the
complex and intricate movements of animated beings." — Popular Science Monthly.

XII.

History of the Conflict between
Religion and Science.

By JOHN WILLIAM DRAPER, M. D., LL. D.,

Author of " The Intellectual Development of Europe."
I vol., i2mo. Price, $1.75.

"This little ' History' would have been a valuable contribution to literature at any
^ime, and is, in fact, an admirable text-book upon a subject that is at present engross-
ing the attention of a large number of the most serious-minded people, and it is no
small compliment to the sagacity of its distinguished author that he has so well gauged
the requirements of the times, and so adequately met them by the preparation of this
volume. It remains to be added that, while the writer has flinched from no responsi-
bility in his statements, and has written with entire fidelity to the demands of truth
and justice, there is not a word in his book that can give offense to candid and fair-
minded readers." — A''. Y. Evening Post.

" The key-note to this volume is found in the antagonism between the progressive
tendencies of the human mind and the pretensions of ecclesiastical authority, as devel-
oped in the history of modern science. No previous writer has treated the subject
from this point of view, and the present monograph will be found to possess no less
originality of conception than vigor of reasoning and wealth of erudition. . . . The
method of Dr. Draper, in his treatment of the various questions that come up for dis-
cussion, is marked by singular impartiality as well as consummate ability. Through-
out his work he maintains the position of an historian, not of an advocate. His tone is
tranquil and serene, as becomes the search after truth, with no trace of the impassioned
ardor of controversy. He endeavors so far to identify himself with the contending
parties as to gain a clear comprehension of their motives, but, at the same time, he
submits their actions to the tests of a cool and impartial examination." — N. Y. Tribune.

D. APPLETON & CO., Publishers, 549 & 551 Broadway, N. Y.

opinions of the Press on the " International Scientific Series P

XIII.

THE DOCTRINE OF

escent, and Darwinism.

By OSCAR SCHMIDT,
PFofessor in the University of Strasburg.

With 26 Woodcuts.
I vol., 121110. Cloth Price, $1.50.

"The entire subject is discussed with a freshness, as well as an elaboration of de-
tail, that renders his work interesting in a more than usual degree. The facts upon
which the Darwinian theory' is based are presented in an effective manner, conclusions
are ably defended, and the question is treated in more compact and available style
than in any other work on the same topic that has yet appeared. It is a valuable ad-
dition to the ' International Scientific Series.' " — Boston Post.

" The present volume is the thirteenth of the 'International Scientific Series,' and
is one of the most interesting of all of them. The subject-matter is handled with a
great deal of skill and earnestness, and the courage of the author in avowing his opin-
ions is much to his credit. . . . This volume certainly merits a careful perusal." —
Hartford Evening Post.

" The volume which Prof. Schmidt has devoted to this theme is a valuable contri-
bution to the Darwinian literature. Philosophical in method, and eminently candid,
it shows not only the ground which Darwin had In his researches made, and conclu-
"sions reached before him to plant his theory upon, but shows, also, what that theory
really Is, a point upon which many good people who talk very earnestly about the
matter are very Imperfectly informed." — Detroit Free Press.

XIV.

The Chemistry of Light and
Photography ;

In its Application to Art, Science, and Industry.

By Dr. HERMANN VOGEI,
Professor In the Royal Industrial Academy of Berlin.

With 100 Illustrations.
i2mo Price, $2.00.

_" Out of Photography has sprung a new science — the Chemistry of Light — and, in
giving apopular view to the one, Dr. Vogel has presented an analysis of the principles
and processes of the other. His treatise is as entertaining as it is instructive, pleas-
antly combining a history of the progress and practice of photography — from the first
rough experiments of Wedgwood and Davy with sensitized paper, in 1802, down to
the latest improvements of the art — with technical illustrations of the scientific theories
on which the art is based. It is the first attempt in any manual of photography to set
forth adequately the just claims of the Invention, both from an artistic and a scientific
point of view, and it must be conceded that the effort has been ably conducted."—'
Chicago Tribune.

D. APPLETON & CO., Publishers, 549 & 551 Broadway, N. Y.

opinions of the Press on the ^^International Scientific Series."*^

XV.

Fungi ;

THEIR NATURE, INFLUENCE, AND USES.

By M. C. COOKE, M. A., LL. Z>.

Edited by Rev. M. J. BERKELEY, M. A., F. L. S.

With 109 Illustrations. Price, $1.50.

"Even if the name of the author of this work were not deservedly eminent, that of
the editor, who has long stood at the head of the British fungologists, would be a suf-
ficient voucher for the accuracy of one of the best botanical monographs ever issued
from the press. . . . The structure, germination, and growth of all these widely-dif-
fused organisms, their habitats and influences for good and evil, are systematically
described." — New York World.

"Dr. Cooke's book contains an admirable rhtinid oi what is known on the struct-
ure, growth, and reproduction of fungi, together with ample bibliographical references .
to original sources of information." — Lo?idoji Athejicewn.

"The production of a work like the one now under review represents a large
amount of laborious, difficult, and critical work, and one in which a serious slip or fatal
error would be one of the easiest matters possible, but, as far as we are able to judge,
the new hand-book seems in every way well suited to the requirements of all beginners
in the difficult and involved study of fungology." — The Gardetier's Chronicle {Lon-
don).

XVI.

The Life and Growth of Language:

AN OUTLINE OF LINGUISTIC SCIENCE.
By WILLIAM DWIGHT WHITNEY,

Professor of Sanskrit and Comparative Philology in Yale College.
I vol., i2mo. Cloth. Price, $1.50.

" Prof Whitney is to be commended for giving to the public the results of his ripe
scholarship and unusually profound researches in simple language. He draws illus-
trations and examples of the principles which he wishes to impact, from common life
and the words in frequent use.

" The topics discussed in this volume are, for the most part, those which have
been already treated by other writers on philology, and even by the author himself, in
his volume on ' Language, and the Study of Language,' published a few years ago,
and, though many of the truths here set forth are those with which students in the
same line of investigation are generally familiar, all will rejoice to see them restated in
such a fresh and simple way.

"This work, while valuable to scholars, will be interesting to every one." — The
Chu7xhma7i. *

" This work is an important contribution to a science which has advanced steadily
under conditions that appear constantly to throw an increasing light on difficult ques-
tions, and at each step clear the way for further discoveries." — Chicago Inter-Occan.

" Prof. Whitney is undoubtedly one of the foremost of English-speaking philologists,
and occupies an enviable position in the wider circle of European students of language.

"His style, clear, simple, picturesque, abounding in striking illustrations, and apt
in comparisons, is admirably fitted to be the vehicle of a popular treatise like the work
under consideration." — Po7-tla7id Daily Press.

D. APPLETON & CO., Publishers, 549 & 551 Broadway, N. Y.

opinions of the Bress on the ''^ International Scientific Series y

XVII.

Money and the Mechanism of Ex-
change.

By W. STANLEY JEVONS, M. A., F, R. S.,

Professor of Logic and Political Economy in the Owens College, Manchester.

I vol., i2mo. Cloth. Price, $1.75.

" He offers us what a clear-sighted, cool-headed, scientific student has to say on the
nature, properties, and natural laws of money, without regard to local interests or na-
tional bias. His work is popularly written, and every page is replete with solid instruc-
tion of a kind that Is just now lamentably needed by multitudes of our people who are
victimized by the grossest fallacies." — Popular Science Monthly.

" If Professor J evons's book is read as extensively as it deserves to be, we shall
have sounder views on the use and abuse of money, and more correct ideas on what a
circulating medium really means." — Boston Saturday Eventing Gazette.

"Professor Jevons writes m a sprightly but colorless style, without trace of either
prejudice or mannerism, and shows no commitment to any theory. The time is not
very far distant, we hope, -when legislators will cease attempting to legislate upon
money before they know what money is, and, as a possible help toward such a change.
Professor Jevons deserves the credit of having made a useful contribution to a depart-
ment of study long too much neglected, but of late years, we are gratified to say, be-
coming less so." — The Financier, New York.

XVIII.

The Nature of Light,

WITH A GENERAL ACCOUNT OF PHYSICAL OPTICS.
By Dr. EUGENE LOMMEL

(University of Erlangen).
I vol., i2mo. Cloth. . . . Price, $2.00.

*' In the present treatise. Professor Lommel has given an admirable outline of the
nature of light and the laws of optics.

" Unlike most other writers on this subject, the author has, we think, wisely post-
poned all reference to theories of the nature of light, until the laws of reflection, re-
fraction, and absorption, have been clearly set before the reader. Then, in the fifteenth
chapter, Professor Lommel discusses Fresnel's famous interference experiment, and
leads the reader to see that the undulatory theory is the only conclusion that can be
satisfactorily arrived at. A clear exposition is now given of Huyglien's theory, after
which follow several chapters on the diffraction and polarization of light-bearing waves.

" The reader is thus led onward much in the same way as the science itself has un-
folded, and this, we think, is the surest and best way of teaching natural knowledge.

"We have said enough to show that Professor Lommel's treatise is a useful contri-
bution to the ' International Series ' — a book that can thoroughly be understood and
enjoyed by any intelligent reader who may not have had any special scientific tram-
ing. ' ' — Nattire.

" In a style singularly lucid, considering the abstruse nature of the subject treated.
Dr. Lommel unfolds the learning of the scientists on the nature and phenomena of
light." — Philadelphia Inquirer.

" As a popular introduction to physical optics, it would be difficult to find a more
satisfactory work than the one by Dr. Lommel, which has just appeared in the excel-
lent ' International Scientific Series.' " — The Eiiglish Mechanic.

D, APPLETON & CO., Publishers, 549 & 551 Broadway, N. Y,

A New Magazine for Students and Cultkated Readers.

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POPULAR SCIENCE MONTHLY,

CONDUCTED BY
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The growing importance of scientific knowledge to all classes of the
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In its literary character, this periodical aims to be popular, without be-
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" In our opinion, the right idea has been happily hit in the plan of this new monthly."
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