Transcriber’s Notes
Obvious typographical errors have been silently corrected. Variations
in hyphenation have been standardised but all other spelling and
punctuation remains unchanged.
Italics are represented thus _italic_, bold thus =bold= and
superscripts thus y^{en}.
WORLDS
IN THE MAKING
THE EVOLUTION OF THE UNIVERSE
BY
SVANTE ARRHENIUS
DIRECTOR OF THE PHYSICO-CHEMICAL NOBEL
INSTITUTE, STOCKHOLM
TRANSLATED BY
DR. H. BORNS
ILLUSTRATED
[colophon]
NEW YORK AND LONDON
HARPER & BROTHERS PUBLISHERS
MCMVIII
Copyright, 1908, by HARPER & BROTHERS.
_All rights reserved._
Published March, 1908.
TABLE OF CONTENTS
I. VOLCANIC PHENOMENA AND EARTHQUAKES 1
Destruction caused by volcanism and by earthquakes.—Different
kinds of volcanoes.—Vesuvius.—Products of eruption.—Volcanic
activity diminishing.—Structure of volcanoes.—Geographical
distribution of volcanoes.—Temperature in the interior of
the earth.—Significance of water for volcanism.—Composition
of the earth’s interior.—Geographical distribution of
earthquakes.—Fissures in the earth’s crust.—Groups of
earthquakes.—Waves in the sea and in the air accompanying
earthquakes.—Their connection with volcanism.—Systems of
fissures.—Seismograms.
II. THE CELESTIAL BODIES, IN PARTICULAR THE EARTH, AS ABODES OF
LIVING BEINGS 39
Manifold character of the worlds.—The earth probably at
first a ball of gases.—Formation of the earth crust and
its rapid cooling.—Balance between heat received and heat
lost by radiation.—Life already existing on the earth for
a milliard of years.—The waste of solar heat.—Temperature
and habitability of the planets.—Heat-preserving influence
of the atmosphere.—Significance of carbon dioxide in the
atmosphere.—Warm and cold geological ages.—Fluctuations in
the percentage of carbon dioxide of the air.—Combustion,
decay, and growth.—Atmospheric oxygen.—Vegetable life more
ancient than animal life.—The atmospheres of planets.—Chances
of an improvement in the climate.
III. RADIATION AND CONSTITUTION OF THE SUN 64
Stability of the solar system.—Losses and possible
gains of heat by the sun.—Theses of Mayer and of
Helmholtz.—Temperatures of the white, yellow, and
reddish stars, and of the sun.—Sun-spots and sun
faculæ.—Prominences.—Spectra of the parts of the
sun.—Temperature of the sun.—The interior of the sun.—Its
composition according to the mechanical theory of heat.—The
losses of heat by the sun probably covered by the enormous
solar energy.
IV. THE RADIATION PRESSURE 94
Newton’s law of gravitation.—Kepler’s observation of comets’
tails.—The thesis of Euler.—Proof of Maxwell.—The radiation
pressure.—Electric charges and condensation.—Comets’ tails
and radiation pressure.—Constituents and properties of comets’
tails.—Weight of the solar corona.—Loss and gain of matter
by the sun.—Nature of meteorites.—Electric charge of the
sun.—Electrons drawn into the sun.—Magnetic properties of
the sun and appearance of the corona.—Constituents of the
meteors.—Nebulæ and their heat and light.
V. THE SOLAR DUST IN THE ATMOSPHERE. POLAR LIGHTS AND THE
VARIATIONS OF TERRESTRIAL MAGNETISM 118
The supply of dust from the sun rather
insignificant.—Polarization of the light of the sky.—The
upper clouds.—Different kinds of auroræ.—Their
connection with the corona of the sun.—Polar lights and
sun-spots.—Periodicity of polar lights.—Polar lights and
magnetic disturbances.—Velocity of solar dust.—Fixation of
atmospheric nitrogen.—The Zodiacal Light.
VI. END OF THE SUN.—ORIGIN OF NEBULÆ 148
The extinction of the sun.—Collision between two celestial
bodies.—The new star in Perseus.—Formation of nebulæ.—The
appearance of nebulæ.—The nebulæ catch wandering meteors and
comets.—The ring nebula in Lyra.—Variable stars.—Eta in
Argus.—Mira Ceti.—Lyra and Algol stars.—Evolution of the
stars.
VII. THE NEBULAR AND THE SOLAR STATES 191
The energy of the universe.—The entropy of the
universe.—The entropy increases in the suns, but
decreases in the nebulæ.—Temperature and constitution
of the nebulæ.—Schuster’s calculations of the condition
of a celestial body consisting of gases.—Action of the
loss of heat on nebulæ and on suns.—Development of a
rotating nebula into a planetary system.—The hypothesis of
Kant-Laplace.—Objections to it.—The views of Chamberlin
and Moulton.—The radiation pressure balances the effect of
Newtonian gravitation.—The emission of gases from the nebulæ
balances the waste of heat characteristic to the solar systems.
VIII. THE SPREADING OF LIFE THROUGH THE UNIVERSE 212
Stability of the species.—Theory of mutation.—Spontaneous
generation.—Bathybius.—Panspermia.—The stand-points of
Richter, Ferdinand Cohn, and Lord Kelvin.—The radiation
pressure enables spores to escape.—The effect of strong
sunlight and of cold on the germinating power.—Transport of
spores through the atmosphere into universal space and through
it to other planets.—General conclusions.
EXPLANATION OF ABBREVIATIONS, ETC.
The temperatures are stated in degrees centigrade (° C.), either on the
Celsius scale, on which the freezing-point of water is 0°, or on the
absolute scale, whose zero lies 273 degrees below the freezing-point of
water, at -273° C. The equivalent temperatures on the Fahrenheit scale
(freezing-point of water 32° F.) are added in brackets (° F.).
1 metre (m.) = 10 decimetres (dm.) = 100 centimetres (cm.) = 1000
millimetres (mm.) = 3.28 ft.; 1 kilometre (km.) = 1000 metres (m.) =
0.62 miles; 1 mile = 1.6 kilometres (km.).
Light travels in vacuo at the rate of 300,000 km. (nearly 200,000
miles) per second.
ILLUSTRATIONS
FIG. PAGE
1. VESUVIUS, AS SEEN FROM THE ISLAND OF NISIDA, IN
MODERATE ACTIVITY 2
2. ERUPTION OF VESUVIUS IN 1882 4
3. ERUPTION OF VESUVIUS IN 1872 6
4. PHOTOGRAPH OF VESUVIUS, 1906. CHIEFLY CLOUDS OF
ASHES 8
5. BLOCK LAVA ON MAUNA LOA 10
6. THE EXCELSIOR GEYSER IN YELLOWSTONE PARK, U. S. A.
REMNANT OF THE POWERFUL VOLCANIC ACTIVITY IN THE
TERTIARY AGE 11
7. MATO TEPEE IN WYOMING, U. S. A. TYPICAL VOLCANIC
“NECK” 12
8. CLEFTS FILLED WITH LAVA AND VOLCANIC CONE OF ASHES,
TOROWHEAP CAÑON, PLATEAU OF COLORADO 13
9. THE KILAUEA CRATER ON HAWAII 15
10. CHIEF EARTHQUAKE CENTRES, ACCORDING TO THE BRITISH
ASSOCIATION COMMITTEE 22
11. CLEFTS IN VALENTIA STREET, SAN FRANCISCO, AFTER THE
EARTHQUAKE OF 1906 25
12. SAND CRATERS AND FISSURES, PRODUCED BY THE CORINTH
EARTHQUAKE OF 1861. IN THE WATER, BRANCHES OF
FLOODED TREES 27
13. EARTHQUAKE LINES IN LOWER AUSTRIA 30
14. LIBERTY BUILDING OF LELAND STANFORD JUNIOR UNIVERSITY,
IN CALIFORNIA, AFTER THE EARTHQUAKE OF 1906 32
15. EARTHQUAKE LINES IN THE TYRRHENIAN DEPRESSION 34
16. SEISMOGRAM RECORDED AT SHIDE, ISLE OF WIGHT, ON
AUGUST 31, 1898 35
17. PHOTOGRAPH OF THE SURFACE OF THE MOON, IN THE VICINITY
OF THE CRATER OF COPERNICUS 62
18. SUN-SPOT GROUP AND GRANULATION OF THE SUN 74
19. PART OF THE SOLAR SPECTRUM OF JANUARY 3, 1872 75
20. METALLIC PROMINENCES IN VORTEX MOTION 76
21. FOUNTAIN-LIKE METALLIC PROMINENCES 76
22. QUIET PROMINENCES OF SMOKE-COLUMN TYPE 77
23. QUIET PROMINENCES, SHAPE OF A TREE 77
24. DIAGRAM ILLUSTRATING THE DIFFERENCES IN THE SPECTRA
OF SUN-SPOTS AND OF THE PHOTOSPHERE 78
25. SPECTRUM OF A SUN-SPOT, THE CENTRAL BAND BETWEEN
THE TWO PORTIONS OF THE PHOTOSPHERE SPECTRUM 78
26. THE GREAT SUN-SPOT OF OCTOBER 9, 1903 79
27. THE GREAT SUN-SPOT OF OCTOBER 9, 1903 80
28. THE GREAT SUN-SPOT OF OCTOBER 9, 1903 81
29. THE GREAT SUN-SPOT OF OCTOBER 9, 1903 82
30. PHOTOGRAPH OF THE SOLAR CORONA OF 1900 83
31. PHOTOGRAPH OF THE SOLAR CORONA OF 1870 84
32. PHOTOGRAPH OF THE SOLAR CORONA OF 1898 85
33. PHOTOGRAPH OF ROERDAM’S COMET (1893 II.), SUGGESTING
SEVERAL STRONG NUCLEI IN THE TAIL 100
34. PHOTOGRAPH OF SWIFT’S COMET (1892 I.) 101
35. DONATI’S COMET AT ITS GREATEST BRILLIANCY IN 1858 102
36. IMITATION OF COMETS’ TAILS 104
37. GRANULAR CHONDRUM FROM THE METEORITE OF SEXES.
ENLARGEMENT 1:70 109
38. ARCH-SHAPED AURORÆ BOREALIS, OBSERVED BY NORDENSKIOLD
DURING THE WINTERING OF THE VEGA IN
BERING STRAIT 1879 124
39. AURORA BOREALIS, WITH RADIAL STREAMERS 125
40. AURORA WITH CORONA, OBSERVED BY GYLLENSKIÖLD ON
SPITZBERGEN, 1883 126
41. POLAR-LIGHT DRAPERIES, OBSERVED IN FINNMARKEN, NORTHERN
NORWAY 127
42. CURVE OF MAGNETIC DECLINATION AT KEW, NEAR LONDON,
ON NOVEMBER 15 AND 16, 1905 138
43. CURVE OF HORIZONTAL INTENSITY AT KEW ON NOVEMBER
15 AND 16, 1905 139
44. ZODIACAL LIGHT IN THE TROPICS 146
45. SPECTRUM OF NOVA AURIGÆ, 1892 154
46. DIAGRAM INDICATING THE CONSEQUENCES OF A COLLISION
BETWEEN TWO EXTINCT SUNS 157
47. SPIRAL NEBULA IN THE CANES VENATICI 159
48. SPIRAL NEBULA IN THE TRIANGLE 161
49. THE GREAT NEBULA IN ANDROMEDA 163
50. RING-SHAPED NEBULA IN LYRA 164
51. CENTRAL PORTION OF THE GREAT NEBULA IN ORION 165
52. NEBULAR STRIÆ IN THE STARS OF THE PLEIADES 167
53. NEBULAR STRIÆ IN THE SWAN 169
54. NEBULA AND STAR RIFT IN THE SWAN, IN THE MILKY WAY 171
55. GREAT NEBULA NEAR RHO, IN OPHIUCHUS 172
56. STAR CLUSTER IN HERCULES 173
57. STAR CLUSTER IN PEGASUS 175
58. CONE-SHAPED STAR CLUSTER IN GEMINI 176
59. COMPARISON OF SPECTRA OF STARS OF CLASSES 2, 3, 4 185
60. COMPARISON OF SPECTRA OF STARS OF CLASSES 2, 3, 4 186
PREFACE
When, more than six years ago, I was writing my _Treatise of Cosmic
Physics_, I found myself confronted with great difficulties. The
views then held would not explain many phenomena, and they failed in
particular in cosmogonic problems. The radiation pressure of light,
which had not, so far, been heeded, seemed to give me the key to the
elucidation of many obscure problems, and I made a large use of this
force in dealing with those phenomena in my treatise.
The explanations which I tentatively offered could, of course, not
claim to stand in all their detail; yet the scientific world received
them with unusual interest and benevolence. Thus encouraged, I tried
to solve more of the numerous important problems, and in the present
volume I have added some further sections to the complex of explanatory
arguments concerning the evolution of the Universe. The foundation
to these explanations was laid in a memoir which I presented to
the Academy of Sciences at Stockholm in 1900. The memoir was soon
afterwards printed in the _Physikalische Zeitschrift_, and the subject
was further developed in my _Treatise of Cosmic Physics_.
It will be objected, and not without justification, that scientific
theses should first be discussed and approved of in competent circles
before they are placed before the public. It cannot be denied that,
if this condition were to be fulfilled, most of the suggestions on
cosmogony that have been published would never have been sent to the
compositors; nor do I deny that the labor spent upon their publication
might have been employed for some better purpose. But several
years have elapsed since my first attempts in this direction were
communicated to scientists. My suggestions have met with a favorable
reception, and I have, during these years, had ample opportunity
carefully to re-examine and to amend my explanations. I therefore feel
justified in submitting my views to a larger circle of readers.
The problem of the evolution of the Universe has always excited
the profound interest of thinking men. And it will, without doubt,
remain the most eminent among all the questions which do not have any
direct, practical bearing. Different ages have arrived at different
solutions to this great problem. Each of these solutions reflected the
stand-point of the natural philosophers of its time. Let me hope that
the considerations which I offer will be worthy of the grand progress
in physics and chemistry that has marked the close of the nineteenth
and the opening of the twentieth century.
Before the indestructibility of energy was understood, cosmogony
merely dealt with the question how matter could have been arranged
in such a manner as to give rise to the actual worlds. The most
remarkable conception of this kind we find in Herschel’s suggestion
of the evolution of stellar nebulæ, and in the thesis of Laplace
concerning the formation of the solar system out of the universal
nebula. Observations more and more tend to confirm Herschel’s view.
The thesis of Laplace, for a long time eulogized as the flower of
cosmogonic speculations, has more and more had to be modified. If we
attempt, with Kant, to conceive how wonderfully organized stellar
systems could originate from absolute chaos, we shall have to admit
that we are attacking a problem which is insoluble in that shape. There
is a contradiction in those very attempts to explain the origin of the
Universe in its totality, as Stallo[1] emphasizes: “The only question
to which a series of phenomena gives legitimate rise relates to their
filiation and interdependence.” I have, therefore, only endeavored to
show how nebulæ may originate from suns and suns from nebulæ; and I
assume that this change has always been proceeding as it is now.
[Footnote 1: Stallo: _Concepts and Theories of Modern Physics_.
London, 1900, p. 276.]
The recognition of the indestructibility of energy seemed to accentuate
the difficulties of the cosmogonic problems. The theses of Mayer and
of Helmholtz, on the manner in which the Sun replenishes its losses of
heat, have had to be abandoned. My explanation is based upon chemical
reactions in the interior of the Sun in accordance with the second law
of thermodynamics. The theory of the “degradation” of energy appeared
to introduce a still greater difficulty. That theory seems to lead to
the inevitable conclusion that the Universe is tending towards the
state which Clausius has designated as “_Wärme Tod_” (heat death),
when all the energy of the Universe will uniformly be distributed
through space in the shape of movements of the smallest particles. That
would imply an absolutely inconceivable end of the development of the
Universe. The way out of this difficulty which I propose comes to this:
the energy is “degraded” in bodies which are in the solar state, and
the energy is “elevated,” raised to a higher level, in bodies which are
in the nebular state.
Finally, I wish to touch upon one cosmogonical question which
has recently become more actual than it used to be. Some kind of
“spontaneous generation,” origination of life from inorganic matter,
had been acquiesced in. But just as the dreams of a spontaneous
generation of energy—_i.e._, of a _perpetuum mobile_—have been
dispelled by the negative results of all experiments in that direction,
just in the same way we shall have to give up the idea of a spontaneous
generation of life after all the repeated disappointments in this field
of investigation. As Helmholtz[2] says, in his popular lecture on the
growth of the planetary system (1871): “It seems to me a perfectly just
scientific procedure, if we, after the failure of all our attempts to
produce organisms from lifeless matter, put the question, whether life
has had a beginning at all, or whether it is not as old as matter, and
whether seeds have not been carried from one planet to another and have
developed everywhere where they have fallen on a fertile soil.”
[Footnote 2: Helmholtz, _Populäré Wissenschaftliche Vorträge_.
Braunschweig, 1876, vol. iii., p. 101.]
This hypothesis is called the hypothesis of panspermia, which I have
modified by combining it with the thesis of the radiation pressure.
My guiding principle in this exposition of cosmogonic problems has been
the conviction that the Universe in its essence has always been what
it is now. Matter, energy, and life have only varied as to shape and
position in space.
THE AUTHOR.
STOCKHOLM, December, 1907.
WORLDS IN THE MAKING
I
VOLCANIC PHENOMENA AND EARTHQUAKES
The Interior of the Earth
The disasters which have recently befallen the flourishing settlements
near Vesuvius and in California have once more directed the attention
of mankind to the terrific forces which manifest themselves by volcanic
eruptions and earthquakes.
The losses of life which have been caused in these two last instances
are, however, insignificant by comparison with those which various
previous catastrophes of this kind have produced. The most violent
volcanic eruption of modern times is no doubt that of August 26 and
27, 1883, by which two-thirds of the island of Krakatoa, 33 square
kilometres (13 square miles) in area, situated in the East Indian
Archipelago, were blown into the air. Although this island was itself
uninhabited, some 40,000 people perished on that occasion, chiefly by
the ocean wave which followed the eruption and which caused disastrous
inundations in the district. Still more terrible was the destruction
wrought by the Calabrian earthquake of February and March, 1783, which
consisted of several earthquake waves. The large town of Messina
was destroyed on February 5th, and the number of people killed by
this event has been estimated at 100,000. The same region, especially
Calabria, has, moreover, frequently been visited by disastrous
earthquakes—again in 1905 and 1907. Another catastrophe upon which
history dwells, owing to the loss of life (not less than 90,000),
was the destruction of the capital of Portugal on November 1, 1755.
Two-thirds of the human lives which this earthquake claimed were
destroyed by a wave 5 m. in height rushing in from the sea.
[Illustration: Fig. 1.—Vesuvius, as seen from the Island of
Nisida, in moderate activity]
Vesuvius is undoubtedly the best studied of all volcanoes. During
the splendor of Rome this mountain was quite peaceful—known as an
extinct volcanic cone so far as history could be traced back. On the
extraordinarily fertile soil about it had arisen big colonies of such
wealth that the district was called Great Greece (Græcia Magna). Then
came, in the year 79 A.D., the devastating eruption which destroyed,
among others, the towns of Herculaneum and Pompeii. The volumes of gas,
rushing forth with extreme violence from the interior of the earth,
pushed aside a large part of the volcanic cone whose remnant is now
called Monte Somma, and the falling masses of ashes, mixed with streams
of lava, built up the new Vesuvius. This mountain has repeatedly
changed its appearance during later eruptions, and was provided with
a new cone of ashes in the year 1906. The outbreak of the year 79
was succeeded by new eruptions in the years 203, 472, 512, 685, 993,
1036, 1139, 1500, 1631, and 1660, at quite irregular intervals. Since
that time Vesuvius has been in almost uninterrupted activity, mostly,
however, of a harmless kind, so that only the cloud of smoke over its
crater indicated that the internal glow was not yet extinguished. Very
violent eruptions took place in the years 1794, 1822, 1872, and 1906.
Other volcanoes behave quite differently from these violent volcanoes,
and do hardly any noteworthy damage. Among these is the crater-island
of Stromboli, situated between Sicily and Calabria. This volcano has
been in continuous activity for thousands of years. Its eruptions
succeed one another at intervals ranging from one minute to twenty
minutes, and its fire serves the sailors as a natural light-house. The
force of this volcano is, of course, unequal at different periods.
In the summer of 1906 it is said to have been in unusually violent
activity. Very quiet, as a rule, are the eruptions of the great
volcanoes on Hawaii.
Foremost among the substances which are ejected from volcanoes is water
vapor. The cloud floating above the crater is, for this reason, the
surest criterion of the activity of the volcano. Violent eruptions
drive the masses of steam up into the air to heights of 8 km. (5
miles), as the illustrations (Figs. 1 to 4) will show.
The height of the cloud may be judged from the height of Vesuvius, 1300
metres (nearly 4300 ft.) above sea-level. The illustration on page 4
(Fig. 2) is a reproduction of a drawing by Poulett Scrope, representing
the Vesuvius eruption of the year 1822. There seems to have been no
wind on this day; the masses of steam formed a cloud of a regular
shape which reminds us of a pine-tree. According to the description of
Plinius, the cloud noticed at the eruption of Vesuvius in the year 79
must have been of the same kind. When the air is not so calm the cloud
assumes a more irregular shape (Fig. 3). Clouds which rise to such
elevations as we have spoken of are distinguished by strong electric
charges. The vivid flashes of lightning which shoot out of the black
clouds add to the terror of the awful spectacle.
[Illustration: Fig. 2.—Eruption of Vesuvius in 1882. (After a
contemporaneous drawing by Poulett Scrope)]
The rain which pours down from this cloud is often mixed with ashes
and is as black as ink. The ashes have a color which varies between
light-gray, yellow-gray, brown, and almost black, and they consist
of minute spherules of lava ejected by the force of the gases and
rapidly congealed by contact with the air. Larger drops of lava harden
to volcanic sand—the so-called “lapilli” (that is, little stones),
or to “bombs,” which are often furrowed by the resistance offered by
the air, and turn pear-shaped. These solid products, as a rule, cause
the greatest damage due to volcanic eruptions. In the year 1906 the
weight of these falling masses (Fig. 4) crushed in the roofs of houses.
A layer of ashes 7 m. (23 ft.) in thickness buried Pompeii under a
protective crust which had covered it up to days of modern excavations.
The fine ashes and the muddy rain clung like a mould of plaster to the
dead bodies. The mud hardened afterwards into a kind of cement, and as
the decomposition products of the dead bodies were washed away, the
moulds have provided us with faithful casts of the objects that had
once been embedded in them. When the ashes fall into the sea, a layer
of volcanic tuffa is formed in a similar manner, which enshrines the
animals of the sea and algæ. Of this kind is the soil of the Campagna
Felice, near Naples. Larger lumps of solid stones with innumerable
bubbles of gases float as pumice-stone on the sea, and are gradually
ground down into volcanic sand by the action of the waves. The floating
pumice-stone has sometimes become dangerous or, at any rate, an
obstacle to shipping, through its large masses; that was, at least, the
case with the Krakatoa eruption of 1883.
[Illustration: Fig. 3.—Eruption of Vesuvius in 1872. (After a
photograph.)]
Among the gases which are ejected in addition to water vapor, carbonic
acid should be mentioned in the first instance; also vapors of
sulphur and sulphuretted hydrogen, hydrochloric acid, and chloride of
ammonium, as well as the chlorides of iron and copper, boric acid, and
other substances. A large portion of these bodies is precipitated on
the edges of the volcano, owing to the sudden cooling of the gases.
The more volatile constituents, such as carbonic acid, sulphuretted
hydrogen, and hydrochloric acid, may spread over large areas, and
destroy all living beings by their heat and poison. It was these gases,
for example, which caused the awful devastation at St. Pierre, where
30,000 human lives were destroyed on May 8, 1902, by the eruption of
Mont Pelée. The ejection of hydrogen gas, which, on emerging from the
lava, is burned to water by the oxygen of the air, has been observed in
the crater of Kilauea.
The ashes of the volcanoes are sometimes carried to vast distances
by the air currents—_e.g._, from the western coast of South America
to the Antilles; from Iceland to Norway and Sweden; from Vesuvius
(1906) to Holstein. Best known in this respect is the eruption of the
Krakatoa, which drove the fine ashes up to an elevation of 30 km. (18
miles). The finest particles of these ashes were slowly carried by
the winds to all parts of the earth, where they caused, during the
following two years, the magnificent sunrises and sunsets which were
spoken of as “the red glows.” This glow was also observed in Europe
after the eruption of Mont Pelée. The dust of Krakatoa further supplied
the material for the so-called “luminous clouds of the night,” which
were seen in the years 1883 to 1892 floating at an elevation of about
80 km. (50 miles), and hence illuminated by the light of the sun long
after sunset.
The crater of Kilauea, on the high volcano of Mauna Loa, in
Hawaii—this volcano is about of the same height as Mont Blanc—has
excited special interest. The crater forms a large lake of lava having
an area of about 12 sq. km. (nearly 5 sq. miles), which, however,
varies considerably with time. The lava boiling at red glow is
constantly emitting masses of gas under slight explosions, spurting
out fiery fountains to a height of 20 m. (65 ft.) into the air. Here
and there lava flows out from crevices in the wall of the crater down
the slope of the mountain, until the surface of the lake of lava
has descended below these cracks. As a rule, this lava is of a thin
fluid consistency, and it spreads, therefore, rather uniformly over
large areas. Of a similar kind are also the floods of lava which are
sometimes poured over thousands of square kilometres on Iceland. The
so-called Laki eruption of the year 1783 was of a specially grand
nature. Though occurring in an uninhabited district, it did a great
amount of damage. In the more ancient geological periods, especially in
the Tertiary age, similar sheets of lava of vast extensions have been
spread over England and Scotland (more than 100,000 sq. km., roughly,
40,000 sq. miles); over Deccan, in India, 400,000 sq. kms. (150,000
sq. miles), up to heights of 2000 m. (6500 ft.); and over Wyoming,
Yellowstone Park, Nevada, Utah, Oregon, and other districts of the
United States, as well as over British Columbia.
[Illustration: Fig. 4.—Photograph of Vesuvius, 1906. Chiefly
clouds of ashes]
In other cases the slowly ejected lava is charged with large volumes of
gases, which escape when the lava congeals and burst it up into rough,
unequal blocks, forming the so-called block lava (Fig. 5). The streams
of lava can likewise produce terrible devastation when they descend
into inhabited districts; on account of their slow motion, they rarely
cause loss of life, however.
Where the volcanic activity gradually lessens or ceases, we can still
trace it by the exhalations of gas and the springs of warm water which
we find in many districts where, during the Tertiary age, powerful
volcanoes were ejecting their streams of lava. To this class belong
the famous geysers of Iceland, of Yellowstone Park (Fig. 6), and
of New Zealand; also the hot springs of Bohemia, so highly valued
therapeutically (_e.g._, the Karlsbad Sprudel); the Fumaroli of Italy,
Greece, and other countries, exhaling water vapor; the Mofettæ, with
their exhalations of carbonic acid (of frequent occurrence in the
district of the Eifel and on both sides of the middle Rhine, in the
Dogs Grotto near Naples, and in the Valley of Death in Java); the
Solfatara, exhaling vapors of sulphur—sulphuretted hydrogen and
sulphur dioxide (they are found near Naples on the Phlegræan Fields
and in Greece); as well as many of the so-called mud volcanoes,
which eject mud, salt water, and gases (as a rule, carbonic acid and
hydrocarbons)—for example, the mud volcanoes near Parma and Modena, in
Italy, and those near Kronstadt, in Transylvania.
[Illustration: Fig. 5.—Block lava on Mauna Loa]
The extinct volcanoes, of which some, like the Aconcagua, 6970 m.
(22,870 ft.), in South America, and the Kilimanjaro, in Africa, 6010
m. (19,750 ft.), rank among the highest mountains, are exposed to a
rapid destruction by the rain, because they consist largely of loose
materials—volcanic ashes with interposed layers of lava. Where these
lava streams expand gradually, they protect the ground underneath from
erosion by water, and in this way proper cuts are formed on the edges
of the lava streams, passing through the old volcano and through the
sedimentary strata at deeper levels.
[Illustration: Fig. 6.—The Excelsior Geyser in Yellowstone
Park, U. S. A. Remnant of powerful volcanic activity in the
Tertiary age]
The old volcano of Monte Venda, near Padua, affords an interesting
example of this type. We can observe there how the sedimentary
limestone has been changed by the lava, which was flowing over it, into
marble to a depth of about 1 m. (3 ft.) Sometimes the limestone which
is lying over the lava has also undergone the same transformation,
which would indicate that lava has not only been flowing above the edge
of the crater, but has also forced itself out on the sides through
the fissures between two layers of limestone. Massive subterranean
lava streams of this kind are found in the so-called lakkolithes of
Utah and in the Caucasus. There the superior layers have been forced
upward by the lava pressing from below; the lava froze, however,
before it reached the surface of the earth, where it might have formed
a volcano. Quite a number of granites, the so-called batholithes,
chiefly occurring in Norway, Scotland, and Java, are of similar origin.
Occasionally it is only the core of congealed lava that has remained of
the whole volcano. These cores, which originally filled the pipe of the
crater, are frequent in Scotland and in North America, where they are
designated “necks” (Fig. 7).
[Illustration: Fig. 7.—Mato Tepee in Wyoming, U. S. A. Typical
volcanic “Neck”]
The so-called cañons of the Colorado Plateau, with their almost
vertical walls, are the results of the erosive action of rivers. A
drawing by Dutton shows a wall of this kind more than 800 m. (2600 ft.)
in height, through four fissures of which lava streams have forced
their way up to the surface (Fig. 8). Over one of these fissures
a small cone of volcanic ashes is still visible, while the cones
which probably overtopped the three other fissures have been washed
away, so that the veins end in small “necks.” Evidently a very fluid
lava—strong percentages of magnesia and of oxide of iron render the
lava more fluid than an admixture of silicic acid, and the fluidity
is further increased by the presence of water—has been forced into
the fissures which were already present, and has reached the surface
of the earth before it froze. The driving force behind them must have
been pretty strong; else the lava streams could not have attained the
necessary velocity of flow.
[Illustration: Fig. 8.—Clefts filled with lava and volcanic
cone of ashes, Torowheap Cañon, Plateau of Colorado. Diagram.]
When the Krakatoa was blown into the air in 1883 half of the
volcano remained behind. This half clearly shows the section of the
cone of ashes, which has been but very slightly affected by the
destructive action of the water. We find there in the central part the
light-colored stopper of lava in the volcano pipe, and issuing from it
more light-colored beds of lava, between which darker strata of ashes
can be seen.
The distribution of volcanoes over the surface of the earth is marked
by striking regularities. Almost all the volcanoes are situated near
the shores of the sea. A few are found in the interior of East Africa;
but they are, at any rate, near the Great Lakes of the equatorial
regions. The few volcanoes which are supposed to be situated in Central
Asia must be regarded as doubtful. We miss, however, volcanoes on
some sea-coasts, as in Australia and along the long coast-lines of
the Northern Arctic Ocean to the north of Asia, Europe, and America.
Volcanoes occur only where great cracks occur in the crust of the earth
along the sea-coast. Where such fissures are found, but where the sea
or large inland lake basins are not near—as, for instance, in the
Austrian Alps—we do not meet with any volcanoes; such districts are,
however, renowned for their earthquakes.
Since ancient ages the belief has been entertained that the molten
masses of the interior of the earth find an outlet through the
volcanoes. Attempts have been made to estimate the depth of the hearths
of volcanoes, but very different values have been deduced. Thus, the
hearth under the volcano of Monte Nuovo, which was thrown up in the
year 1538 on the Phlegræan Fields, near Naples, has been credited with
depths varying from 1.3 km. to 60 km. (1 mile to 40 miles); for the
Krakatoa, estimates of more than 50 km. (30 miles) have been made. All
these calculations are rather aimless; for the volcanoes are probably
situated on folds of the earth-crust, through which the fluid mass (the
magma) rushes forth in wedges from the interior of the earth, and it
will presumably be very difficult to say where the hearth of magma ends
and where the volcanic pipe commences. The Kilauea gives the visitor
the impression that he is standing over an opening in the crust of the
earth, through which the molten mass rushes forth directly from the
interior of the earth. (Fig. 9.)
[Illustration: Fig. 9.—The Kilauea Crater on Hawaii]
As regards the earth-crust, we know from observations in bore-holes
made in different parts of the world that the temperature increases
rather rapidly with the depth, on an average by about thirty degrees
Cent. per kilometre (about 1.6° F. per 100 feet). It must be remarked,
however, that the depth of our deepest bore-holes hardly exceeds 2
km. (Paruchowitz, in Silesia, 2003 m., or 6570 ft.; Schladebach,
near Merseburg, Prussian Saxony, 1720 m.). If the temperature should
go on increasing at the rate of 30 degrees Cent. for each further
kilometre, the temperature at a depth of 40 kilometres should attain
degrees at which all the common rocks would melt. But the melting-point
certainly rises at the same time as the pressure. The importance of
this circumstance was, however, much exaggerated when it was believed
that for this reason the interior of the earth might possibly be solid.
Tammann has shown by direct experiments that the temperature of fusion
only rises up to a certain pressure, and that it begins to decrease
again on a further increase of pressure. The depths indicated above are
therefore not quite correct. If we assume, however, that other kinds of
rock behave like diabase—the melting-point of which, according to the
determinations of Barus, rises by 1° Cent. for each 40 atmospheres of
pressure corresponding to a depth of 155 m.—we should conclude that
the solid crust of the earth could not have a greater thickness than 50
or 60 km. (40 miles). At greater depths we should therefore penetrate
into the fused mass. On account of its smaller density the silicic acid
will be concentrated in the upper strata of the molten mass, while
the basic portions of the magma, which are richer in iron oxide, will
collect in the lower strata, owing to their greater density.
This magma we have to picture to ourselves as an extremely viscid
liquid resembling asphalt. The experiments of Day and Allen show that
rods, supported at their ends, of 30 × 2 × 1 mm. of different minerals,
like the feldspars microcline and albite, could retain their shape for
three hours without curving noticeably, although their temperature was
about a hundred degrees above their melting-point, and although they
appeared completely fused, or, more correctly, completely vitrified
when taken out of the furnace. These molten silicates behave very
differently from other liquids like water and mercury, with which we
are more accustomed to deal.
The motion and diffusion in the magma, and especially in the very
viscous and sluggish acid portions of the upper strata, will therefore
be exceedingly small, and the magma will behave almost like a solid
body, like the minerals of the experiments of Day and Allen. The magmas
of volcanoes like Etna, Vesuvius, and Pantellaria may, therefore, have
quite different compositions, as we should conclude from their lavas
without our being forced to believe, with Stübel, that these three
hearths of volcanoes are completely separated, though not far removed
from one another. In the lava of Vesuvius a temperature of 1000 or 1100
degrees has been found at the lower extremity of the stream. From the
occurrence in the lava of certain crystals like leucite and olivin,
which we have reason to assume must have been formed before the lava
left the crater, it has been concluded that the lava temperature cannot
have been higher than 1400 degrees before it left the volcanic pipe.
It would, however, be erroneous to deduce from the temperature of the
lava of Vesuvius that the hearth of the volcano must be situated at a
depth of approximately 50 kilometres. Most likely its depth is much
smaller, perhaps not even 10 kilometres. For there, as everywhere where
volcanoes occur, the crust of the earth is strongly furrowed, and the
magma will just at the spots where we find volcanoes come much nearer
to the surface of the earth than elsewhere.
The importance of water for the formation of volcanoes probably lies
in the fact that, in the neighborhood of cracks under the bottom of
the sea, the water penetrates down to considerable depths. When the
water reaches a stratum of a temperature of 365 degrees—the so-called
critical temperature of water—it can no longer remain in the liquid
state. That would not prevent, however, its penetrating still farther
into the depths, in spite of its gaseous condition. As soon as the
vapor comes in contact with magma, it will eagerly be absorbed by the
magma. The reason is that water of a temperature of more than 300
degrees is a stronger acid than silicic acid; the latter is therefore
expelled by it from its compounds, the silicates, which form the main
constituents of the magma. The higher the temperature, the greater the
power of the magma to absorb water. Owing to this absorption the magma
swells and becomes at the same time more fluid. The magma is therefore
pressed out by the action of a pressure which is analogous to the
osmotic pressure by virtue of which water penetrates through a membrane
into a solution of sugar or salt. This pressure may become equivalent
to thousands of atmospheres, and this very pressure would raise the
magma up the volcanic pipe even to a height of 6000 m. (20,000 feet)
above the sea-level. As the magma is ascending in the volcanic pipe
it is slowly cooled, and its capacity for binding water diminishes
with falling temperature. The water will hence escape under violent
ebullition, tearing drops and larger lumps of lava with it, which fall
down again as ashes or pumice-stone. After the lava has flown out of
the crater and is slowly cooling, it continues to give off water,
breaking up under the formation of block lava (see Fig. 5). If, on the
other hand, the lava in the crater of the volcano is comparatively
at rest, as in Kilauea, the water will escape more slowly; owing to
the long-continued contact of the surface layer of lava with the air,
little water will remain in it, the water being, so to say, removed by
aeration, and the lava streams will therefore, when congealing, form
more smooth surfaces.
In some cases volcanoes have been proved (Stübel and Branco) not to
be in connection with any fractures in the crust of the earth. That
holds, for instance, for several volcanoes of the early Tertiary age
in Swabia. We may imagine that the pressure produced by the swelling
of the magma became so powerful as to be able to break through the
earth-crust at thinner spots, even in the absence of previous fissures.
If, in our consideration, we follow the magma farther into the depths,
we shall not find any reason for assuming that the temperature will not
rise farther towards the interior of the earth. At depths of 300 or
400 km. (250 miles) the temperature must finally attain degrees such
that no substance will be able to exist in any other state than the
gaseous. Within this layer the interior of the earth must, therefore,
be gaseous. From our knowledge of the behavior of gases at high
temperatures and pressures, we may safely conclude that the gases in
the central portions of the earth will behave almost like an extremely
viscid magma. In certain respects they may probably be compared to
solid bodies; their compressibility, in particular, will be very small.
We might think that we could not possibly learn anything concerning
the condition of those strata. Earthquakes have, however, supplied us
with a little information. Such gaseous masses must fill by far the
greatest part of the earth, and they must have a very high specific
gravity; for the average density of the earth is 5.52, and the outer
strata, the ocean and the masses of the surface which are known to us,
have smaller densities. The ordinary rocks possess a density ranging
from 2.5 to 3. It must, therefore, be assumed that the materials of
the innermost portions of the earth must be metallic, and Wiechert,
in particular, has advocated this view. Iron will presumably form the
chief constituent of this gas of the central earth. Spectrum analysis
teaches us that iron is a very important constituent of the sun. We
know, further, that the metallic portions of the meteorites consist
essentially of iron; and finally terrestrial magnetism indicates that
there must be large masses of iron in the interior of the earth.
We have also reason to believe that the native iron occurring in
nature—_e.g._, the well-known iron of Ovifak, in Greenland—is of
volcanic origin. The materials in the gaseous interior of the earth
will, owing to their high density, behave in chemical and physical
respects like liquids. As substances like iron will, also at very high
temperatures, have a far higher specific gravity than their oxides,
and these again have a higher gravity than their silicates, we have to
assume that the gases in the core of the earth will almost exclusively
be metallic, that the outer portions of the core will contain
essentially oxides, and those farther out again mostly silicates.
The fused magma will, on penetrating in the shape of batholithes
into the upper layers, probably be divided into two portions, of
which one, the lighter and gaseous, will contain water and substances
soluble in it; while the other, heavier portion, will essentially
consist of silicates with a lower percentage of water. The more fluid
portion, richer in water, will be secreted in the higher layers, will
penetrate into the surrounding sedimentary strata, especially into
their fissures, and will fill them with large crystals, often of
metallurgical value—_e.g._, of the ores of tin, copper, and other
metals, while the water will slowly evaporate through the superposed
strata. The more viscid and sluggish mass of silicates, on the other
hand, will congeal, thanks to its great viscosity, to glass, or, when
the cooling is very slow, to small crystals.
We now turn to earthquakes. No country has been absolutely spared by
earthquakes. In the districts bounding upon the Baltic, and especially
in northern Russia, they have, however, been of a quite harmless type.
The reason is that the earth-crust there has been lying undisturbed for
long geological epochs and has never been fractured. The comparatively
severe earthquake which shook the west coast of Sweden on October 23,
1904, to an unusually heavy degree, without, however, causing any
noteworthy damage (a few chimneys were knocked over), was caused by a
fault of relatively pronounced character for those districts in the
Skager-Rack—a continuation of the deepest fold in the bottom of the
North Sea, the so-called Norwegian Trough, which runs parallel to the
Norwegian coast. In Germany, the Vogtland and the districts on both
sides of the middle Rhine have frequently been visited by earthquakes.
Of other European countries, Switzerland, Spain, Italy, and the Balkan
Peninsula, as well as the Karst districts of Austria, have often
suffered from earthquakes.
[Illustration: Fig. 10.—Chief earthquake centres, according to
the British Association Committee]
According to the committee appointed by the British Association for the
investigation of earthquakes—a committee which has contributed a great
deal to our knowledge of these great natural phenomena—earthquakes of
some importance emanate from certain centres which have been indicated
on the subjoined map (Fig. 10). The most important among these regions
comprises Farther India, the Sunda Isles, New Guinea, and Northern
Australia; it is marked on the map by the letter F. From this district
have emanated in the six-year period 1899-1904 no fewer than 249
earthquakes, which have been recorded in many observatories far removed
from one another. This earthquake centre F is closely related to the
one marked E, in Japan, from which 189 earthquakes have proceeded. Next
to this comes the extensive district K with 174 earthquakes, comprising
the most important folds in the crust of the Old World, including
the mountain chains from the Alps to the Himalaya. This district is
interesting, because it has been disturbed by a great many earthquakes,
although it is almost entirely situated on the Continent. After that
we have the districts A, B, C, with 125, 98, and 95 earthquakes. They
are situated near lines of fracture in the earth-crust along the
American coast of the Pacific Ocean and the Caribbean Sea. District D,
with 78 earthquakes, is similarly situated. The three last-mentioned
districts, B, C, D, as well as G, between Madagascar and India, with
85 earthquakes, all seem to be surpassed by the district H in the
eastern Atlantic, with its 107 earthquakes. These latter are, however,
relatively feeble, and we owe their accurate records probably to the
circumstances that a great many earthquake observatories are situated
within the immediate surroundings of this district. The same may be
said of the district I, or Newfoundland, which is not characterized
by many earthquakes, and of the district J, between Iceland and
Spitzbergen, with 31 and 19 earthquakes respectively. The last on
the list used to be the district L, situated about the South Pole,
with only eight earthquakes. This small number is probably merely
due to the want of observatories in those parts of the earth. Another
district, M, has finally been added, which extends to the southwest
from New Zealand. No fewer than 75 intense earthquakes were recorded
between March 14 and November 23, 1903, by the Discovery Expedition, in
70° southern latitude and 178° eastern longitude.
Earthquakes commonly occur in swarms or groups. Thus, more than 2000
shocks were counted on Hawaii in March, 1868. During the earthquakes
which devastated the district of Phokis, in Greece, in 1870-73, shocks
succeeded one another for a long time at intervals of three seconds.
During the whole period of three and a half years about half a million
shocks were counted, and, further, a quarter of a million subterranean
reports which were not accompanied by noticeable concussions. Yet of
all these shocks only about 300 did noteworthy damage, and only 35
were considered worth being reported in the newspapers. The concussion
of October 23, 1904, belonged to a group which lasted from October
10 to October 28, and in which numerous small tremors were noticed,
especially on October 24 and 25. The earthquake of San Francisco
commenced on April 18, 1906, at 5 hrs. 12 min. 6 sec. A.M. (Pacific
Ocean time), and ended at 5 hrs. 13 min. 11 sec, lasting therefore 1
minute and 5 seconds. Twelve smaller shocks succeeded in the following
hour. Before 6 hrs. 52 min. P.M., nineteen further concussions were
counted, and various smaller shocks succeeded in the following days.